MINISTRY OF EDUCATION AND TRAININGHO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION GRADUATION THESIS MAJOR: FOOD TECHNOLOGY INSTRUCTOR: NGUYEN VINH TIEN NGUYEN LE KHANH LINH PH-SE
INTRODUCTION
Research Problem
1.1.1 pH-sensitive Films pH-sensitive films are designed to monitor pH changes by exhibiting distinct color changes, which can indicate spoilage or contamination, making them valuable in food packaging applications The inclusion of natural pigments like anthocyanins enhances the environmental friendliness of these films (Silva-Pereira et al., 2015) The effectiveness of these films lies in the careful selection and combination of various components, each contributing to the film's overall properties and performance.
Starch, particularly tapioca starch, is a popular natural polymer known for its film-forming abilities, clarity, flexibility, and oxygen barrier properties However, pure starch films often lack mechanical strength and can be brittle, which leads to the need for incorporating additional materials Polyvinyl alcohol (PVA), a synthetic polymer recognized for its biodegradability and non-toxicity, enhances the mechanical strength and water resistance of starch-based films The combination of PVA and starch not only improves flexibility but also reduces brittleness, making these films ideal for various applications, including food packaging.
Karaya gum, derived from the Sterculia tree, serves as a natural thickening agent and stabilizer in film formulations, enhancing flexibility and providing a uniform coating while improving biodegradability and mechanical properties (Choudhary et al., 2024) The films incorporate natural pigments, specifically anthocyanins from red cabbage, which impart vibrant red, purple, and blue hues Red cabbage extract is particularly notable for its effectiveness as a pH indicator, exhibiting distinct color changes across a broad pH range (Castañeda-Ovando et al., 2009) Additionally, these pigments offer antioxidant benefits, further enhancing the film's functionality.
The strategic integration of starch, PVA, karaya gum, and anthocyanins results in a multifunctional pH-sensitive film that excels in food monitoring and electrochemical printing Starch serves as the foundational matrix, while PVA improves mechanical properties and flexibility Karaya gum contributes to uniformity and additional flexibility, and anthocyanins provide pH sensitivity and antioxidant advantages This combination effectively addresses performance and sustainability challenges.
Electrochemical printing is an innovative technique that leverages chemical reactions to alter the color of pH-sensitive materials, enabling the printing of information on polymer films without relying on synthetic inks This method presents numerous advantages, underscoring its uniqueness and importance in modern printing technologies.
Electrochemical printing offers exceptional precision in material creation and modification on substrates, facilitating the intricate printing of designs with minimal waste This high level of accuracy enables the precise deposition of active substances responsive to environmental changes, such as pH variations, making it particularly suitable for detailed monitoring applications in food packaging (Zhai, Li et al 2018).
This technique enhances food safety by eliminating the use of synthetic inks, which can introduce harmful contaminants By utilizing natural pigments such as anthocyanins in the electrochemical process, the risk of ink migration into food products is significantly reduced.
Previous studies have predominantly focused on polymer films with charged components, leading to the production of two primary colors: red/pink and green/yellow (Zhai, Li et al 2018; Yang, Zhai et al 2021) In contrast, the current research explores the application of neutral polymers, which have been less studied Utilizing neutral polymers could enhance the range of color changes and minimize interactions with charged contaminants, thereby expanding the potential applications of pH-sensitive films across diverse fields.
The aim of advancing printed polymer films is to improve the preservation of perishable goods by offering real-time insights into the condition of food products with limited shelf lives This technology allows consumers to easily detect spoilage and enhances food safety, ultimately boosting consumer confidence while minimizing food waste through more precise freshness indicators.
The integration of electrochemical printing with pH-sensitive films marks a major breakthrough in food monitoring technologies By utilizing the distinct properties of starch, PVA, karaya gum, and anthocyanins, this innovative approach creates multifunctional films that cater to diverse applications This research seeks to fill existing gaps in food safety and advance sustainability in packaging technologies.
Research Objectives
This experiment aims to explore the effects of different components in the formulation of pH-sensitive polymer films The study focuses on optimizing these films by assessing the impact of hydrolyzed karaya gum, varying concentrations of red cabbage extract rich in anthocyanins, and the quantity of glycerol used as a plasticizer.
Hydrolyzed Karaya Gum Ratio: Assess how different ratios of hydrolyzed karaya gum impact the film's overall properties, including its mechanical strength, flexibility, and uniformity.
Anthocyanin Concentration: Evaluate the effects of varying the concentration of anthocyanins in the red cabbage extract on the film's pH sensitivity, color change response, and stability.
Glycerol Content: Investigate the role of glycerol as a plasticizer in the film formulation, determining its effect on the film's flexibility, brittleness, and overall mechanical properties.
Physical Properties: Measure the film's thickness, transparency, moisture content, and water solubility.
Mechanical Properties: Evaluate tensile strength, elongation at break, and flexibility to ensure the film meets the required standards for practical applications.
Structural Characteristics: Use Fourier-transform infrared spectroscopy (FTIR) to analyze the molecular interactions and structural integrity of the films.
Chemical Properties: Assess the antioxidant capacity and pH sensitivity of the films through color change measurements, ensuring the film's effectiveness in real-world applications.
Electrolyte Composition: Examine the effect of anthocyanin concentration in the electrolyte solution on the quality and precision of electrochemical printing.
Voltage: Determine the optimal voltage required for effective electrochemical printing,ensuring clear and accurate deposition of the pH-sensitive material.
Printing Time: Investigate the impact of different printing durations on the quality and durability of the printed information, aiming to establish the best parameters for practical use.
Significance in Science and Practice
This research significantly advances material science by developing pH-sensitive polymer films from natural pigments, such as anthocyanins from red cabbage It introduces innovative electrochemical printing techniques that replace synthetic inks, enhancing food safety by minimizing contamination risks The study contributes to sustainable packaging by creating biodegradable films capable of real-time food quality monitoring, thereby reducing food waste Additionally, it explores neutral polymers, which offer versatile applications beyond food packaging Overall, this research provides economic and environmental benefits, supporting global efforts for sustainable and safe packaging technologies.
LITERATURE REVIEW
Active and Intelligent Packaging
Active and intelligent packaging refers to technologies that modify the environment of packaged food to enhance its shelf life, ensure safety, and improve sensory attributes, all while preserving the food's quality (de Kruijf, van Beest et al 2002).
Intelligent packaging systems monitor the condition of packaged foods and provide information about the quality of the food during transport and storage.
Biodegradable films are eco-friendly layers crafted from natural biological materials, intended to decompose naturally These films can be utilized on or between food items, enhancing preservation and sustainability The primary materials used in their production include polysaccharides, proteins, and lipids, which can be combined to create mixtures with improved technological properties.
Films play crucial roles in food packaging, including informing consumers about food quality and safety through smart films, maintaining freshness with bioactive films, and delivering beneficial compounds Each type of eco-friendly film offers unique advantages tailored to specific purposes Packaging is essential for protecting contents from contamination and spoilage, facilitating transport and storage, and ensuring uniform measurement Therefore, the four primary functions of packaging—containment, protection, convenience, and communication—are interrelated and must be considered collectively for effective food preservation.
Despite traditional packaging's emphasis on sustainability, it often falls short of consumer expectations As a result, the demand for intelligent and active films is rising globally Consumers are increasingly concerned about food quality and seek more information about their products, which must be effectively communicated through packaging without compromising its integrity.
Smart films serve as innovative tools that indicate pH changes, monitor temperature, and track fruit ripening, making it easy for consumers of all ages and education levels to assess food quality These films utilize a pH-indicator function to effectively detect changes during food deterioration, enabling real-time monitoring of food quality while in storage Consequently, consumers can visually differentiate between fresh and spoiled food through a simple color change, eliminating the need to open packaging.
The growing concern over the environmental damage caused by petroleum-based food packaging has sparked significant interest in the development of natural and biodegradable alternatives within the industry.
The rising consumer demand for health, nutrition, food safety, and environmental sustainability has driven significant research into the properties of biopolymer films, resulting in the creation of edible films for food packaging.
Polysaccharide Materials
Polyvinyl alcohol is an odorless substance available in white to cream-colored granules or powder form Its pure aqueous solutions are typically neutral or slightly acidic, which may lead to susceptibility to mold growth.
Plastic film materials are widely used due to their convenience in production, but advancements in technology have accelerated their evolution, resulting in significant environmental challenges like "white pollution." Common types of plastic films, including polyethylene (PE), polypropylene (PP), and polyvinyl chloride (PVC), are favored for their excellent barrier properties, high mechanical strength, and transparency, contributing to their extensive application across various industries.
Plastic film contributes to significant environmental waste, as it can take hundreds of years to decompose into harmless molecules like CO2 and H2O This prolonged degradation process leads to considerable ecological harm.
Polyvinyl alcohol (PVA) is the only vinyl polymer that can act as a carbon and energy source for bacteria, allowing for its breakdown by bacterial action and enzymes (Liu, Deng et al 2019) This capability enables PVA to degrade up to 75% within 46 days, categorizing it as a biodegradable polymer material (Chiellini, Corti et al 2003).
PVA film is an excellent alternative to non-degradable materials such as polyethylene and polypropylene due to its flexibility, transparency, and non-toxic nature It is biocompatible, offers strong mechanical properties, and demonstrates chemical resistance and gas barrier capabilities Its complete degradability meets the increasing demand for eco-friendly solutions, making the shift from non-degradable materials to biodegradable PVA film a significant trend for the future.
Figure 1 The structure of Polyvinyl Alcohol (PVA)
Figure 2 Tai Ky Tapioca powder
Tapioca starch is extracted from the cassava plant, which thrives in equatorial regions between the Tropic of Cancer and the Tropic of Capricorn The cassava plant is known by various names globally, including yucca in Central America, mandioca or manioca in Brazil, and cassada in Africa and Southeast Asia In North America and Europe, "cassava" typically refers to the plant's roots, while "tapioca" denotes the starch and processed products derived from them The cassava plant is a member of the spurge family (Euphorbiaceae).
Starch stands out among natural polymers as one of the most promising materials for the future due to its attractive combination of affordability, abundance, and thermoplastic behavior
Figure 3 The composition of starch
Its potential as a material for edible films has been widely acknowledged Edible films crafted from carbohydrates, including starch, typically exhibit greater mechanical strength and serve as effective gas barriers.
Tapioca starch-based edible films possess several advantageous properties, including isotropy, which ensures uniformity in all directions, and they are odorless, tasteless, and colorless, making them ideal for diverse food applications These films are non-toxic, biodegradable, and contribute to environmental sustainability Additionally, cassava starch films exhibit excellent flexibility and low water permeability, enhancing their suitability as edible films They also serve as effective barriers to oxygen, preserving the quality and freshness of packaged food products.
Karaya gum is primarily composed of heavily acetylated units, featuring α-D-galacturonic acid and α-L-rhamnose as its main chain components The structure includes O-4 linkage of the acid to O-2 of rhamnose, along with β-D-glucuronic acid present in the side chains Additionally, approximately half of the rhamnose units are connected to β-D-galactose at O-4 via a 1,4 linkage (Stephen and Phillips 2016).
2.2.3.2 Role in Film Formation and Applications
Karaya film exhibits insufficient tensile strength, making it difficult to peel off from casting surfaces in one piece Despite this limitation, it provides a uniform coating that dries without cracking The film's tackiness allows for strong adhesion to surfaces, a trait common among tree exudates While karaya film is soluble in cold water, its high viscosity results in a slower dissolution rate in the mouth.
Active Substance - Anthocyanin
Anthocyanins are essential pigments found in all plant tissues, responsible for the red, purple, and blue colors in various fruits, vegetables, flowers, and grains The name "Anthocyanin" is derived from the Greek words "Anthos," meaning "Flower," and "Kyanos," meaning "Blue." These naturally occurring compounds belong to the flavonoid class of phytochemicals and their color can vary with changes in pH Beyond their aesthetic appeal, anthocyanins play a crucial role in health by neutralizing free radicals, which protects cells from oxidative damage, slows aging, and lowers the risk of chronic diseases Additionally, they exhibit anti-inflammatory properties that may help mitigate chronic inflammatory conditions Anthocyanins are commonly used as natural colorants in food and beverage products.
Anthocyanins, water-soluble pigments prevalent in most vascular plants, are categorized as a subgroup of secondary plant metabolites known as flavonoids (Alappat and Alappat
Anthocyanidins are the foundational structures of anthocyanins, featuring a flavylium ion at their core, which consists of a C6-C3-C6 flavonoid framework This structure is complemented by a fused aromatic A ring, a heterocyclic benzopyran C ring, and a phenyl B ring When anthocyanidins are bonded to sugar molecules, they are classified as anthocyanins.
Figure 4 Primary composition of anthocyanins
Over 600 anthocyanins have been identified from various plant species, distinguished by factors such as hydroxyl group quantity, sugar characteristics, and the nature of carboxylates linked to the sugar The structural variations in flavylium cations lead to diverse anthocyanidins, with cyanidin, pelargonidin, peonidin, delphinidin, malvidin, and petunidin being the most prevalent The color and stability of anthocyanins are influenced by the hydroxylation and methylation of the B-ring, where increased hydroxyl groups enhance blueness and methylation boosts redness Cyanidin is the most abundant anthocyanidin, making up about 50% of the total, while malvidin and petunidin are the least common at 7% These compounds are primarily found in red, purple, or blue fruits, flowers, and leaves, including raspberries, daisies, roses, irises, and red grapes.
Table 1 The six most common anthocyanidins in vascular plants Anthocyanidin Abbreviation Percentage Alteration pattern (-R) Color
Pelargonidin Pg 12% OH OH H OH H OH H Orange
Cyanidin Cy 50% OH OH H OH OH OH H Orange red
Peonidin Pn 12% OH OH H OH OCH3 OH H Red
Delphinidin Dp 12% OH OH H OH OH OH OH Bluish red
Petunidin Pt 7% OH OH H OH OCH3 OH OH Bluish red
Malvidin Mv 7% OH OH H OH OCH3 OH OCH3 Bluish red
Glycosylation and acylation are essential processes in the biosynthesis of anthocyanins, significantly enhancing their structural diversity Glycosylation primarily involves the enzymatic attachment of sugar molecules, mainly glucose, at the C3 position of anthocyanidins, leading to red color shifts and improved stability Additionally, various sugars participate in this modification In contrast, acylation occurs when sugar residues are modified by aromatic or aliphatic acids, which are crucial for color alteration and stability enhancement through co-pigmentation reactions, resulting in a shift towards blue hues.
Figure 5 Some saccharides participating in anthocyanin modification
Figure 6 Typical acid components of the acylation in anthocyanins pH Sensitivity and Color Change Mechanism
Anthocyanin color is significantly influenced by factors such as structure, pH, temperature, enzymatic activity, UV radiation, co-pigmentation, and oxygen presence These pigments can exhibit a range of colors, including salmon-pink, red, violet, and blue, depending on the pH level Specifically, anthocyanins tend to appear reddish in acidic environments, pink in neutral conditions, and blue in basic settings Their color-changing property is linked to their ionic nature, and they are most stable in highly acidic conditions, where flavylium cations enhance their solubility in aqueous solutions.
Anthocyanins exhibit different chemical forms based on the solution's pH, significantly affecting their color At a pH of 1, the flavylium cation, which imparts red hues, is the most prevalent Between pH levels 2 and 4, blue quinoidal species dominate, while at pH 5 to 6, anthocyanins primarily exist as two colorless forms: a carbinol pseudobase and a chalcone Above pH 7, the stability of anthocyanins declines, leading to degradation influenced by their substituent groups.
Within the pH range of 4 to 6, four structural forms of anthocyanins coexist: the flavylium cation, anhydrous quinoidal base, colorless carbinol base, and pale yellow chalcone The equilibrium between the quinoidal base and carbinol pseudobase is influenced by the flavylium cation As pH increases, the equilibrium shifts towards the anhydrous base, while acidic conditions enhance the stability of the red flavylium ion In alkaline environments, anthocyanins are more susceptible to degradation, resulting in the formation of phenolic acids and aldehydes.
Figure 7 Anthocyanins exhibit different chemical structures based on pH, alongside degradation reactions (with R1 as either H or a saccharide, and R2 and R3 as H or methyl)
The stability of anthocyanidins, particularly influenced by substituents on the B ring and additional hydroxyl or methoxyl groups, varies significantly, with pelargonidin (Pg) being the most stable Monoglycosides and diglycosides exhibit greater stability in neutral pH due to the protective effect of sugar molecules, which help prevent the degradation of unstable intermediates into phenolic acids and aldehydes These degradation pathways underscore the complexity and sensitivity of anthocyanin compounds to pH changes, which greatly affect their color and stability in various applications.
Antioxidant Properties and Health Benefits
Anthocyanins are powerful antioxidants that neutralize reactive free radicals by donating electrons or hydrogen atoms Their effectiveness as antioxidants is closely related to their oxidation ease, and research indicates that the anthocyanin content in fruits and vegetables directly enhances their antioxidant activity This contributes to protective effects against degenerative and chronic diseases Moreover, plant and fruit extracts high in phenolic compounds have been shown to inhibit mutagenesis and carcinogenesis.
Anthocyanins and various phytochemicals, such as flavonoids, chlorophyll derivatives, tocopherols, carotenoids, and ascorbic acid, exhibit antioxidant activity by stabilizing free radicals These compounds effectively neutralize harmful free radicals, including singlet oxygen, superoxide radicals, hydroxyl radicals, and hydrogen peroxide, which can cause lipid peroxidation in cell membranes In catechols, oxidation occurs through free radicals, leading to the formation of stable semiquinones Compounds containing catechol groups or 1,4-hydroquinone are particularly prone to oxidation, as the phenoxyl radical's stability, aided by oxygen, prevents it from extracting hydrogen from other substances, allowing it to react with another semiquinone to produce a quinone and a phenol group.
Cyanidin is an anthocyanidin with di-hydroxy groups (o-dihydroxyl) on the B ring of the flavonoid structure, including two hydroxyl groups (-OH) at positions 3' and 4' on the
Cyanidin (Cy), an anthocyanin, exhibits antioxidative properties by neutralizing reactive alkoxy free radicals (ROã) When Cy encounters these free radicals, it donates a hydrogen atom from its hydroxyl group, converting the harmful RO free radical into a harmless molecule (ROH) This process results in the formation of a phenoxyl free radical, which is stable and non-toxic to cells due to its capacity to bind with oxygen.
Figure 8 The stabilization of the Cyanidin (Cy) semiquinone radical is achieved through resonance
The phenoxyl radical stabilizes by interacting with oxygen to create a stable semiquinone structure, which prevents further oxidation by not readily reacting with other molecules This semiquinone can react with another free radical, forming a quinone molecule and a phenol group, thus reducing free radicals in cells and minimizing oxidative damage Anthocyanidins with ortho-dihydroxyl substitutions, like cyanidin, delphinidin, and petunidin, are more prone to oxidation, whereas those without, such as pelargonidin, peonidin, and malvidin, exhibit greater resistance, with pelargonidin being particularly stable at neutral pH.
Anthocyanidins and anthocyanins exhibit greater antioxidant activity than vitamins C and E, effectively neutralizing free radicals by donating phenolic hydrogen atoms, which enhances their anticarcinogenic effects Research indicates a direct correlation between antioxidant capacity and anthocyanin levels in various berries, showcasing their strong ability to scavenge reactive oxygen species.
2.3.2 Red cabbage – Noteworthy source of anthocyanins
Anthocyanins are found in various parts of fruits and vegetables, including organs, roots, leaves, stems, and specific grains Rich sources of anthocyanins include purple corn, chokeberry, and blueberries Key anthocyanidins like cyanidin, delphinidin, and pelargonidin account for a significant portion of anthocyanins in flowers, fruits, and leaves Notably, cyanidin-3-glucoside is the most abundant anthocyanin in fruits, with red cabbage recognized as a significant source of cyanidin anthocyanins (Roy and Rhim 2021).
Cabbage, or Brassica oleracea L var capitata, belongs to the Cruciferae family and is notable for its cross-like petal arrangement This genus includes various leafy vegetables such as broccoli, cauliflower, bok choy, turnips, and Brussels sprouts Originally from the Mediterranean and first cultivated in Western Europe, cabbage is now mainly produced in China, which harvested 35 billion kilograms in 2022 The edible head of cabbage features tightly packed leaves that come in different shapes, sizes, colors, and textures, with major varieties including red, white, and savoy cabbage, all of which can be prepared in numerous culinary ways.
Introduction to Electrochemical Printing
Packaging is essential for preserving food quality, offering protection against environmental, chemical, and physical threats It prevents breakage and acts as a barrier to moisture, oxygen, carbon dioxide, and other gases, as well as flavors and aromas Moreover, effective packaging blocks light to safeguard nutrients and colors, while modern solutions actively maintain the ideal atmosphere around the product.
The Industrial Revolution brought about innovative manufacturing processes and materials, which later found valuable applications in food packaging One notable example is metal cans, initially created for snuff, which effectively preserve moisture and flavor This advancement paved the way for the canning process developed by Nicholas Appert, who responded to a challenge from French Emperor Napoleon Bonaparte to create a method for food preservation for his army.
Electrochemical reactions convert chemical energy into electrical energy and enable the movement of electrons In electrochemical printing, these reactions facilitate the creation and modification of materials on a film, leading to the formation of intricate printed patterns.
Electrochemical reactions facilitate the conversion of chemical energy to electrical energy and the reverse, driven by electron movement In electrochemical printing, these reactions play a crucial role in creating and modifying materials on a film, leading to the development of intricate printed patterns.
Anode (Positive Electrode): The site where oxidation occurs, meaning molecules or ions lose electrons.
Cathode (Negative Electrode): The site where reduction occurs, meaning molecules or ions gain electrons.
The electrolyte solution contains free-moving ions that facilitate electrical conductivity between the electrodes In this context, the electrolyte solution also contains anthocyanin, a natural pigment.
At the anode, oxidation reactions occur, resulting in the production of H+ ions, which increases acidity and alters the local pH, potentially affecting the color of anthocyanins present A key example of this process is the oxidation of water, where molecules or ions in the solution lose electrons.
Reactions at the Cathode: This reaction decreases H+ ions (increasing alkalinity) and changes the local pH at the cathode, affecting the color of anthocyanin.
At the cathode, molecules or ions in the solution undergo reduction, gaining electrons.
An example of this reaction is the reduction of H+ ions:
2.4.4 Factors Affecting the Electrochemical Printing Process with Anthocyanin and Polymer-Based Films
The voltage applied between electrodes significantly influences the speed and direction of electrochemical reactions While higher voltage can enhance reaction rates, it risks unwanted decomposition of the electrolyte or polymer film Conversely, lower voltage may slow the process but allows for improved control over the desired reactions.
The current used in the printing process significantly influences both the deposition of anthocyanin and the clarity of the printed patterns A higher current can lead to thicker layers, but it risks local overheating and potential damage to the film Conversely, a lower current facilitates the formation of thinner and more uniform layers, although it results in a longer printing duration.
Ion Concentration: The ion concentration in the electrolyte determines the conductivity and stability of the electrochemical reactions Higher ion concentration increases conductivity but may cause precipitation or unwanted decomposition.
The concentration of anthocyanins significantly influences the color intensity of prints, with higher concentrations yielding more vibrant hues; however, this can compromise the adhesion and durability of the resulting film Additionally, the pH level of the electrolyte plays a crucial role in determining the color of anthocyanin and the stability of electrochemical reactions, allowing for adjustments to be made to enhance color control and optimize the printing process.
Various materials, including gold, platinum, carbon, and other metals, exhibit distinct catalytic properties and durability, which significantly influence the efficiency and accuracy of the printing process Carbon electrodes are favored for their excellent conductivity and affordability, whereas gold and platinum electrodes offer superior chemical stability, albeit at a higher cost.
The dimensions and configuration of electrodes play a crucial role in determining the distribution of the electric field and the accuracy of the printed patterns Utilizing smaller and intricately shaped electrodes enables the production of finer details in the printed designs.
The temperature during the printing process significantly influences the reaction rate and durability of the polymer film, with higher temperatures accelerating reactions but potentially leading to undesirable changes in the film's structure Additionally, environmental factors like humidity play a crucial role in the printing process and the stability of the final printed pattern, as elevated humidity levels can diminish both adhesion and the overall durability of the film.
System Design and Configuration: The arrangement and distance between the electrodes affect the electric field and the distribution of electrochemical reactions on the film surface.
Mask and mold design is essential for achieving intricate and precise details in printing By utilizing masks, the contact area of the electric field can be effectively controlled, while molds play a crucial role in shaping the final print This combination allows for the creation of complex patterns and enhanced design accuracy.
MATERIALS AND RESEARCH METHODS
Hydrolysation of Resin from Sterculia foetida
The alkaline treatment of tragacanth gum was performed based on the method outlined by Postulkova, Chamradova et al (2017), with modifications Initially, 2 grams of tragacanth gum powder were mixed with 100 mL of distilled water to form a 2% w/v suspension at room temperature After 24 hours, 33.3 mL of 1M NaOH was added (maintaining a 3:1 ratio), and the mixture was stirred for 30 minutes To neutralize excess NaOH following the dissolution of the gum, 1M HCl was introduced, and stirring continued for an additional 30 minutes The dissolved gum was then precipitated by adding 83 mL of 99% ethanol (in a 2:1 ratio), followed by filtration to collect the precipitate The precipitated gum was washed twice with 75% ethanol, cut into small pieces, and dried at 50°C for 24 hours Finally, the dried samples were ground into powder and stored in glass jars.
Figure 10 Process diagram for collecting karaya gum
Extraction of anthocyanins from purple cabbage
The objective of this study is to extract anthocyanin compounds from purple cabbage for research purposes, analyze their content, and investigate the color changes of anthocyanins in response to different pH levels Furthermore, the extracted anthocyanin solution will be incorporated into various polymer matrices to evaluate the properties of active films derived from purple cabbage anthocyanin.
The extraction of anthocyanin was conducted following the methodology of El-Naggar, El-Newehy et al (2021), with slight modifications to fit our laboratory conditions, as illustrated in Figure 11 We carefully selected fresh purple cabbage with a deep, vibrant color, ensuring it was free from damage and dryness to optimize anthocyanin yield The cabbage samples were meticulously separated from the leaves and white veins, followed by thorough washing under running water to eliminate any dirt residues.
Figure 11 Flow chart of the extraction process from purple cabbage
To prepare the extract, blend 100g of processed purple cabbage with 300g of distilled water in a 1:3 ratio until smooth Heat the mixture in a stainless steel pot on an induction cooker to 50°C for 30 minutes After heating, coarsely filter the mixture using a cloth filter and filter paper to eliminate residues Store the final extract in dark glass bottles wrapped in aluminum foil to reduce light exposure, and keep it at 4°C for future experiments Multiple extractions were performed to ensure consistency, and a UV-Vis spectrophotometer was utilized to standardize the samples.
Film development
This study aims to identify the optimal membrane based on formation efficiency, observability, and cost-effectiveness We produced a range of desirable film samples using two primary polymers, starch and PVA Subsequently, we performed analytical measurements to assess how the selected components affect the properties of the films and the electrochemical printing method.
Figure 12 Overview of the experiment process when changing 3 factors: extract, base film ratio, glycerol
The film formation methodology is depicted in a flowchart (Figure 12), focusing on the impact of hydrolyzed karaya gum substitution, red cabbage extract ratios, and glycerol plasticizer content on film properties The polymer films are modified in thickness by adjusting the total polymer content and extraction ratios, with composition parameters detailed in Table 4 Solutions of starch, PVA, and hydrolyzed gum arabic were prepared at a uniform concentration of 3%, dissolving 3g of each polymer in 100ml of distilled water through heating A fixed starch blending ratio of 50:50 was maintained, and experiments with various polymers were conducted, leading to the selection of PVA despite its higher cost, prompting the inclusion of tapioca starch as a cost-effective alternative while preserving membrane properties Each film type received specific amounts of glycerol, red cabbage extract, and potassium sulfate for electrochemical applications, maintaining a total polysaccharide content of 0.75g, except in one electrochemical printing study The polymer solutions were concentrated to 6% for optimal film coating, and films were cast onto 90mm plastic Petri dishes, dried at 50°C for 24 hours, and stored at 75% RH for 48 hours for stabilization before characterization.
Figure 13 Films after drying and preservation Table 4 Film formulation for one casting
Total content (g) of Cassava starch and
Modifications to the supplementary gum karaya content
Modifications to the red cabbage extract content
Modifications to the glycerol content
Characterization of red cabbage extract
3.5.1 Determine the absorption spectrum and ability to change color according to pH of purple cabbage extract.
This study aims to investigate the color-changing properties and absorption spectrum of a dye substance in response to solutions with varying pH levels By examining these reactions, we can identify the different forms of anthocyanin and their corresponding colors across a range of pH values.
The color of purple cabbage extract dye varies with pH changes due to alterations in its chemical structure, affecting absorption spectra and peaks Below pH 3.0, red cabbage anthocyanins exist primarily as red cationic flavilium As the pH increases to 6.0, the anthocyanins transition to a neutral quinoidal base, changing the color from red to purple At pH 7.0, the solution takes on a blue hue due to the formation of anionic and natural quinonoidal bases Further increases in pH beyond 7.0 result in the creation of natural and anionic chalcones, leading to a green color, although the quinonoidal base remains the dominant anthocyanin structure (Ghareaghajlou, Hallaj-Nezhadi et al 2021).
To assess the pH sensitivity of the extract, 0.5 mL is diluted in 5 mL of various buffer solutions with pH levels ranging from 2 to 12 The UV-Vis spectra for these 11 solutions are captured using a UV-Vis spectrophotometer (UH-3500 Hitachi) across wavelengths from 380 nm.
760 nm The result of (Freitas, Silva et al 2020) with different methods and ratios, it still demonstrates the variation of the extract when pH is altered.
Figure 14 The alteration of color in anthocyanin-rich extract from red cabbage across varying pH levels
3.5.2 Total Monomeric Anthocyanin Pigment Content.
Purpose: Determine the total anthocyanin content in purple cabbage extract.
Monomeric anthocyanin pigments demonstrate reversible color changes when exposed to different pH levels, with the colored oxonium form dominating at pH 1.0 and the colorless hemiketal form at pH 4.5 The absorbance of these pigments at 520 nm is directly related to their concentration, specifically focusing on cyanidin-3-glucoside content In contrast, polymeric anthocyanins, which are degraded, do not change color with varying pH and are excluded from measurements due to their absorption characteristics at both pH levels.
Procedure: Preparing pH 4,5 and pH 1.0.
Table 5 Preparing pH 4,5 and pH 1.0 pH 1.0
To prepare a pH 1.0 buffer solution using potassium chloride (0.025M), weigh 1.86 g of KCl and dissolve it in about 980 mL of distilled water Measure the pH and adjust it to 1.0 (±0.05) by adding approximately 6.3 mL of HCl Finally, transfer the solution to a 1 L volumetric flask and dilute to the mark with distilled water For a pH 4.5 buffer, sodium acetate at a concentration of 0.4M is used.
54.43 g of CH3CO2Naã3H2O is weighed into a beaker, and diluted with distilled water to approximately 960 mL The pH is measured and adjusted to 4.5 (±0.05) using approximately 20 mL of HCl The solution is then transferred to a 1 L volumetric flask and diluted to volume with distilled water.
To prepare the sample, take 1 mL of purple cabbage extract (1:5 dilution) and add 4 mL of pH 1.0 and 4.5 buffer solutions in a test tube Shake well and allow the reaction to proceed for 15 minutes Then, transfer the sample to a cuvette, filling it to two-thirds full, for absorbance and absorption spectrum measurement using a Hitachi UH-3500 UV-Vis spectrophotometer Measure the maximum absorbance at 520 nm and 700 nm, using distilled water as the blank Calculate the results using the formula: A = (A520nm – A700nm)pH 1.0 – (A520nm – A700nm)pH 4.5.
MW (molecular weight) = 449.2 g/mol for cyanidin-3-glucoside (cyd-3-glu)
DF = dilution factor established in D l = pathlength in cm; e = 26 900 molar extinction coefficient, in L ´ mol–1 ´ cm–1, for cyd-3-glu
1000 = factor for conversion from g to mg.
Determine the percentage of anthocyanin in the extract according to research by Huynh Thi Kim Cuc et al., 2013.
Where: a: the amount of anthocyanin (g); w: moisture content (%) (Huynh Thi Kim Cuc et al., 2013).
Determination of film properties
Measuring Lab color parameters allows researchers to evaluate color variation in samples as the concentration of non-anthocyanin-extracted purple cabbage changes From these measurements, ∆E is calculated to assess the differences in color among the films.
A colorimeter functions on the principle of light absorption and reflection by a sample It begins by emitting light at specific wavelengths from a standard source, followed by the adjustment of filters to isolate these wavelengths, including red, green, and blue The light is then directed onto the sample, where it is partially absorbed and partially reflected, depending on the sample's chemical structure and color The resulting light intensities are converted into electrical signals, which are processed to calculate colorimetric values like Lab* or RGB, providing a detailed description of the sample's color characteristics.
In this study, we employed a modified color measurement method based on the approach by Qin, Liu et al (2019) to suit our experimental conditions Films were prepared using varying concentrations of purple cabbage extract, following a controlled formula The Linshang LS171 colorimeter was precisely positioned on the film surface to ensure complete sensor contact After initiating the measurement, the LS171 emitted light and recorded color data through its light sensor Upon completion, the device displayed key color parameters, including Lab*, which are essential for our analysis.
- Lfor lightness ranging from 0 (black) to 100 (white),
- a(-80 - 100) for red-green intensity where negative values denote green and positive denote red,
- b (-80 - 70) for yellow-blue intensity where negative values indicate blue-green and positive indicate yellow.
Measurements are repeated at three different positions on the film Subsequently, these values are utilized to compute the total color difference (∆E):
∆E = (� ∗ − �) 2 + (� ∗ − �) 2 + (� ∗ − �) 2 where L*, a*, and b* represent the color parameters of standard white paper and L, a, and b denote the color parameters of the film samples.
3.6.2 Moisture content and water solubility
This method effectively measures the moisture content and water solubility of polymer films, facilitating the assessment of their physical properties and suitability for various environmental conditions By accurately gauging moisture levels, it helps control hydration and improve barrier properties, while the evaluation of water solubility aids in determining biodegradability and film performance in wet environments.
To assess the moisture content and water solubility of polymer films, an experimental method was adapted from previous studies by Gontard et al (1992) and Jimenez et al (2012) Initially, the polymer film sample is precisely weighed using an analytical balance to obtain its initial mass (m0) The sample is then dried in a Yamato DKM600 convection oven at 105°C for 24 hours until its weight stabilizes over three consecutive measurements, ensuring all moisture is removed After drying, the sample cools in a desiccator before being weighed again to determine the mass post-drying (m1) The moisture content of the film is subsequently calculated using a specific equation.
To assess water solubility, a dried film sample (m1) is submerged in 50 ml of distilled water at room temperature for one hour After immersion, any undissolved material is re-dried under identical conditions, and the final mass (m2) is measured The percentage of water solubility of the film is then calculated using the appropriate formula.
Measuring film thickness is essential for accurately assessing the films' properties, including mechanical strength and barrier performance To achieve this, film samples are preserved and then measured using an ACCUD electronic depth gauge (Germany) at ten random positions, following ASTM D374-99 (2010) standards The procedure involves positioning the film between the micrometer's anvil and spindle, gently closing the spindle until it lightly contacts the film, and recording the thickness This process is repeated at various locations to ensure comprehensive thickness evaluation and to identify any variations.
This study investigates the percentage of light transmission through synthetic film samples utilizing varying formulas of resin (0%, 10%, 20%, 30%), glycerol (0g, 0.05g, 0.1g, 0.15g, 0.2g), and extracted solutions (0ml, 5ml, 10ml, 15ml, 20ml) within the visible light spectrum of 360 nm to 780 nm.
A spectrophotometer emits a beam of light with wavelengths between 360 nm and 780 nm, which passes through a membrane sample Absorbing molecules within the sample absorb some of the transmitted light, as noted by Perkampus (2013).
The filming samples were stored in a NaCl solution bath at 75% relative humidity and 25°C for 48 hours After preparation, the samples, measuring 1×6 cm, were placed directly into the measuring slot of the Hitachi UH-3500 UV-Vis spectrophotometer Scanning parameters were set to a wavelength range of 360 to 780 nm to measure transmittance (%T).
Purpose: Determining which type has the highest and lowest moisture transmission capabilities is crucial for their application in food products.
The Desiccant Method involves sealing filming samples onto the mouth of a test cup filled with desiccant material This setup is then placed in a moisture-controlled environment, where it is periodically weighed to measure the rate of water vapor movement from the sample into the desiccant.
The moisture vapor transmission rate (WVP) of the film is assessed by weighing samples stored in a NaCl solution at room temperature (30°C) for 2 days Afterward, the samples are fixed onto glass jars filled with dry silica gel to maintain a relative humidity of 0% These jars are then placed in a saturated NaCl solution at 23% RH and allowed to stabilize for 1 hour Initial weights are recorded, followed by measurements every 24 hours for 6 days to track weight changes The water vapor transmission rate (WVTR) and water vapor permeability (WVP) of the film samples are calculated using the formula established by Debeaufort, Voilley et al (1994).
Delta m :The increasing weight of glass jar:
A :The area of the mouth of the glass jar (m²) t : Time of water vapor transmission (h) x: The thickness of the sample film (mm).
Delta P : The vapor pressure difference across the film (P53.55 Pa).
Determining the optimal membrane type for load-bearing capacity is vital, especially in food applications where mechanical properties play a key role A higher load-bearing capacity enhances food protection, making it essential to assess the mechanical properties of various membrane samples.
The tensile testing machine clamps a film sample measuring 1cm x 5cm, applying a constant pulling speed As the clamps move apart, the distance increases until the sample breaks, allowing for the recording of both the pulling force and elongation The tensile strength of the film is then determined by calculating the maximum load applied at the rupture point.
Membrane samples are prepared by storing them in a saturated NaCl solution at 25°C for two days before analysis Each sample is then cut into 1×5 cm pieces and secured in the testing apparatus The WinTest Analysis software is utilized to manage the equipment settings, with the initial length set at 3 cm, a pulling speed of 40 mm/m, and an initial activation force of 0.05 N Each sample undergoes five measurements, and the average value is documented for accuracy.
Fmax : The maximum tensile force of the membrane at the point of rupture (N). r : initial width of film (mm) r =1.5mm x : The thickness of the film
Purpose: Investigate the chemical interactions of single membranes between anthocyanin molecules and polymers, as well as other components within the membrane.
Evaluation of the film antioxidant potential
This study aims to explore the antioxidant potential of membrane samples enhanced with alcohol-extracted solutions in water, simulating both oil-loving and water-loving foods The research highlights that a gradual increase in anthocyanins significantly boosts the antioxidant capacity of the membrane samples, emphasizing the importance of extraction ratios in enhancing antioxidant properties.
The evaluation of a polymer film's antioxidant potential focuses on its capacity to scavenge free radicals and inhibit oxidation processes This assessment typically involves spectrophotometric assays, where the film's antioxidant compounds interact with stable free radicals, such as the deep violet ABTS radical When these antioxidants reduce the ABTS radical, the color diminishes, allowing for the measurement of absorbance changes to determine the film's effectiveness in neutralizing oxidative agents.
The experiment followed the modified methodology of Brand-Williams, Cuvelier et al (1995) to assess the antioxidant potential of polymer films using the ABTS assay An ABTS solution was prepared in methanol at a known concentration, and the polymer film was cut into uniform pieces before being immersed in the solution The mixture was incubated in the dark for a designated time, typically 10 minutes, to avoid light-induced degradation, after which the absorbance of the solution was measured.
723 nm before and after incubation using a UV-Vis spectrophotometer Calculate the percentage of ABTS radical scavenging activity using the formula:
Procedure: Prepare ABTS Solution (7 mM):Weigh approximately 0.0194 g of ABTS and dissolve it in 5 mL of distilled water or ultra-pure water to create a 7 mM ABTS solution.
Prepare Ammonium Persulfate Solution (2.45 mM):Weigh approximately 0.0066 g of ammonium persulfate and dissolve it in 10 mL of distilled water or ultra-pure water to create a 2.45 mM solution.
To create the ABTS+ radical cation, mix equal parts of a 7 mM ABTS solution and a 2.45 mM ammonium persulfate solution, such as 5 mL of each Stir the mixture and allow it to sit at room temperature in the dark for 24 hours, during which the ammonium persulfate will oxidize the ABTS, resulting in the formation of the green-colored ABTS+ radical cation.
To prepare the ABTS+ solution, incubate it and then dilute with phosphate buffer at pH 7.4 until the absorbance at 734 nm reaches approximately 0.70 (± 0.02) Utilize a UV-Vis spectrophotometer for measuring absorbance and adjust the concentration accordingly.
Investigation of the pH-dependent color change ability of the films
The objective of this study is to evaluate how the films respond to variations in buffer solution pH, aiming to optimize anthocyanin concentration for specific color changes Additionally, the research explores the potential use of these films in monitoring food spoilage effectively.
The film samples demonstrate color changes due to variations in anthocyanin forms influenced by different environmental conditions, leading to corresponding alterations in color parameters (Lab).
The color measurement method utilized in this study follows the approach outlined by Kuswandi, Wicaksono et al (2011) Dried and preserved films are cut into 2×2 cm samples and immersed in buffer solutions with pH levels ranging from 2 to 12 for 3 minutes, using 10 ml of each solution in Petri dishes After immersion, the samples are dried on filter paper in a Yamato DKM600 convection drying oven before color measurement The Lab* values are analyzed, and the ∆E values are subsequently calculated.
This study aims to explore the color variations in membrane samples under varying voltage conditions, different electrolysis exposure times, extract concentration levels, and film thicknesses The objective is to identify which membrane sample demonstrates the most optimal coloration, a factor that is essential for enhancing packaging printing quality.
The color of anthocyanins is influenced by pH levels, as demonstrated in the study by Zhai et al (2018) When the needle is connected to the anode of an electrochemical workstation, it creates a localized low pH environment within the hydrogel, causing anthocyanins to change color to orange-red due to their conversion from anhydrobase to flavylium ion In contrast, connecting the electrode tip to the cathode generates a localized high pH environment, resulting in a color shift to yellow as anthocyanins transform from anhydrobase to anhydrobase anion.
Film samples measuring 3×3 cm were prepared and stored for two days in a saturated NaCl solution at 23% relative humidity and 25°C Electrochemical printing was conducted under controlled conditions tailored to specific investigative goals, following a protocol detailed in Table 4 for assessing changes in extraction ratios Additional experiments included electrode reversal, variations in power supply voltage, and adjustments to printing duration The films were integrated into a specialized electrochemical printing system, as illustrated in Figure 16 Once connected to the printing device, each film was exposed to a printing template for a designated time while a constant electrical current was applied, resulting in a color change at the contact points of the template pattern on the film surface This color alteration was analyzed using the Linshang LS171 colorimeter, as previously described.
RESULTS AND DISCUSSION
Characterization of red cabbage anthocyanins
Anthocyanin compounds as pH indicators through color variation
The anthocyanin extract from purple cabbage exhibits a pH-dependent color change, making it essential for research and experimentation Our analysis involved reacting the extract with buffer solutions across a pH range of 2.0 to 12.0 to observe color variations The results, illustrated in Figure 17, show that at pH 2 to 4, the extract appears deep red, transitioning to deep purple between pH 5 and 6 Under neutral conditions (pH 6 to 8), the color shifts to pale purple or bluish-green, and at pH levels from 9 to 12, it turns yellow or green This phenomenon aligns with previous studies (Yong, Wang et al 2019; Qin, Liu et al 2019; Tang, He et al 2019; Prietto, Mirapalhete et al 2017), as depicted in Figure 18, which explains that the color change results from the structural transformation of anthocyanins.
Figure 17 The color change of purple cabbage extract in different pH buffer solutions (pH2-12)
Figure 18 The structural changes of anthocyanins (Abedi-Firoozjah, Yousefi et al 2022)
Freshly prepared purple cabbage extract typically appears purple at a neutral pH of 6-7 However, when the pH is lowered to an acidic level (pH < 2) using a buffer solution, the anthocyanins in the extract transform into Flavylium cations, resulting in a red color In an acidic environment rich in H+ ions, these ions interact with the anthocyanins, forming red-colored compounds known as Flavylium cations (AH+).
As the pH increases from 1.0 to 4.0, the concentration of H+ ions decreases, leading to a gradual transition from red to pink at pH 4.0 In the pH range of 5.0 to 6.0, the anthocyanin structure predominantly reflects the original purple color of the cabbage, indicating that under these weakly acidic conditions, anthocyanins exist in the quinoidal base form This balance between acid and base results in a characteristic pale to deep purple color of purple cabbage extract.
As the pH rises from 6.0 to 7.0-8.0, the quinoidal base, which appears purple, undergoes deprotonation and changes into an anionic quinoidal base, resulting in a blue color in a neutral environment At pH 9.0, anthocyanins transition into a colorless carbinol pseudo base form, acquiring additional -OH groups on their molecular rings.
As the pH level exceeds 10.0, anthocyanins experience a ring-opening transformation, resulting in the formation of chalcones that exhibit yellow to green hues This process involves the alteration of the anthocyanin molecule from a quinoidal base with a purple color, characterized by a three-ring structure, to a two-ring chalcone structure that appears green to yellow Consequently, the coloration of anthocyanin solutions is influenced by the varying proportions of these structural forms at specific pH levels.
UV-vis spectroscopy of anthocyanins in different buffer soloution
The absorption spectrum of anthocyanin from red cabbage extract, analyzed between 360nm and 780nm, reveals that as pH increases, the maximum absorption value (ABS) of anthocyanin decreases, with a shift in maximum absorption wavelength towards longer wavelengths In acidic conditions (pH 1-4), the maximum ABS value drops significantly from 1.471 to 0.422, stabilizing between pH 5 to 8, before declining sharply to 0.245 at pH 10 The peak absorption wavelength shifts from approximately 523nm at pH 1 to 587-594nm at pH 10 These changes in maximum absorption value and wavelength are attributed to the transformation of anthocyanin's forms in relation to pH levels In strong acids, the Flavylium cation form is prone to oxidation or hydrolysis, leading to color loss and reduced absorption Conversely, in alkaline conditions, anthocyanin converts to the chalcone form, causing significant color loss due to structural changes induced by OH- ions Each anthocyanin form has unique light absorption properties at varying wavelengths.
The structural changes of anthocyanin in response to pH variations result in shifts in its maximum absorption wavelength within the absorption spectrum, aligning with experimental findings from Ahmadiani, Robbins et al (2014).
Research indicates that the absorption characteristics of anthocyanins are influenced by pH levels Specifically, as the pH transitions from acidic to alkaline, there is a notable decrease in the maximum absorption value, accompanied by an increase in wavelength, which signifies alterations in the molecular structure of anthocyanins.
Figure 19 The absorption spectrum of anthocyanin extract from purple cabbage in pH buffer solutions (pH 2.0 – 12.0).
Anthocyanin quantity in red cabbage extract
Table 6 Maximum absorbance value in 2 buffer solutions at 2 wavelengths
The maximum absorption values of purple cabbage extract containing anthocyanins were analyzed at two pH levels and wavelengths At 520 nm, pH 1 showed a significantly higher absorbance of 2.821 ± 0.037 compared to 0.503 ± 0.033 at pH 4.5 Conversely, at 700 nm, pH 1 had a lower absorbance of 0.056 ± 0.023 than pH 4.5's 0.123 ± 0.012 This absorbance difference is attributed to monomeric anthocyanin pigments, which exhibit reversible color changes with pH; the colored oxonium form dominates at pH 1, while the colorless hemiketal form prevails at pH 4.5 The pigment absorbance at 520 nm correlates with pigment concentration, with results based on cyanidin-3-glucoside content The average total anthocyanin content was calculated to be 696.168 ± 5.748 mg/L, resulting in a percentage of 0.815% ± 0.007 in fresh purple cabbage using water as the extraction solvent Although our water-based extraction method yielded lower anthocyanin content compared to other methods, it still supports the development of environmentally friendly biodegradable packaging, minimizing chemical waste and environmental impact.
Figure 20 Structures showing both the flavylium cation (A) and its hemiketal form (B), adorned with either RZH or glycosidic substituents
Physical attributes of film samples
Table 7 Color parameters and and total color difference values
Thickness significantly affects the Water Vapor Permeability (WVP) and Tensile Strength (TS) of food packaging films This article examines the thickness parameters of polymer films made from PVA and cassava starch, as illustrated in Fig 1 Additionally, it evaluates how varying levels of hydrolyzed karaya gum substitution, red cabbage extract ratios rich in anthocyanins, and plasticizer content influence film thickness.
Figure 21 Film samples’ thickness Effect of Hydrolyzed Karaya Gum Substitution :
Increasing the content of hydrolyzed karaya gum in PVA-cassava starch films results in a slight decrease in thickness, with measurements dropping from 0.141 mm at 0% karaya gum to 0.121 mm at 30% karaya gum The significant reduction in thickness between films without karaya gum and those with 30% substitution highlights the impact of hydrolyzed karaya gum on film properties However, lower substitution levels of 10% and 20% do not significantly affect thickness This behavior can be attributed to phase separation that occurs when PVA and cassava starch interact, due to their differing chemical properties and interaction capabilities.
The incorporation of karaya gum significantly improves the interactions between film phases by creating cross-links among molecules, resulting in a denser film structure and reduced overall film thickness (Kim, Sessa et al 2004) Additionally, research on corn starch films crosslinked with citric acid and/or maleic anhydride indicates that altering the substitution levels of hydrolyzed karaya gum notably impacts film thickness, with the most substantial reduction observed at a 30% substitution level.
Increasing the ratio of red cabbage extract in PVA-starch films significantly enhances film thickness, rising from an average of 0.132 mm at 0% extract content to 0.169 mm at 20% extract content Statistically significant differences (p < 0.05) are observed between films without extract and those with the highest extract ratio, indicating the extract's impact However, lower extract levels (5g and 10g) do not produce notable thickness changes, as the additional mass and volume from the red cabbage extract contribute to overall thickness The addition of 15 and 20 grams of extract creates more complex matrices, further increasing film thickness These findings align with previous research by Yan Qin et al., which reported similar thickness increases in cassava starch films with higher fruit powder content.
The thickness of PVA-cassava starch films increases with higher glycerol content, rising from 0.124 mm at 0g glycerol to 0.154 mm at 0.2g glycerol (p < 0.05) This effect is most pronounced in films containing substantial glycerol concentrations (13.33%, 20%, and 26.67% based on polymer weight) Glycerol acts as a plasticizer, enhancing the mobility and flexibility of the film network, which results in a less dense structure compared to films with lower glycerol content Consequently, the increased free volume allows polymer chains to move more freely and occupy more space Research by Sanyang, Sapuan et al (2016) confirms that glycerol addition leads to increased film thickness due to its plasticizing properties In summary, incorporating glycerol significantly enhances the thickness of PVA-cassava starch films, particularly at concentrations of around 15% or higher.
4.2.3 Moisture content and water solubility
Figure 22 Moisture contents and water solubility of films changing karaya gum Moisture Content Analysis:
The addition of karaya gum results in minor variations in the moisture content of films, with a slight decrease observed at 10% karaya gum (SP10G), followed by stability at 20% (SP20G) and an increase at 30% (SP30G) This indicates that karaya gum has a limited effect on moisture content, suggesting that the base polymer matrix plays a more significant role in moisture retention, while karaya gum contributes only marginally.
The addition of karaya gum to the films significantly improves their water solubility, demonstrating a clear trend of increased hydrophilicity Notably, the transition from SP20G to SP30G reveals a remarkable rise in water solubility from 30% to 45%, indicating that higher concentrations of karaya gum greatly enhance the films' interaction with water.
Mechanistic Insights: (Shanbhag, Shenoy et al 2023)
Hydrophilicity: Karaya gum contains numerous hydroxyl groups that form hydrogen bonds with water molecules, increasing the overall solubility of the film in water.
Polymer-Gum Interaction: The interaction between karaya gum and the base polymer could also alter the polymer network, making it more accessible to water molecules.
Packaging Materials: The choice of karaya gum content can be tailored depending on the requirement for water resistance or solubility.
Figure 23 Moisture contents and water solubility of films changing red cabbage extract Moisture Content Analysis:
The addition of red cabbage extract results in minor fluctuations in the moisture content of the films, which remains stable between 18% and 22% This indicates that red cabbage extract has a limited effect on moisture levels However, at higher concentrations of 15 mL and 20 mL, there is a slight increase, likely due to the hygroscopic properties of certain components in the extract that enhance the film's moisture retention capabilities.
The addition of red cabbage extract significantly boosts the water solubility of the films, demonstrating enhanced hydrophilic properties Notably, a sharp increase in solubility occurs between the 15 mL and 20 mL concentrations, with solubility rising from 45% to 50% This indicates that higher concentrations of red cabbage extract greatly improve the films' interaction with water.
Mechanistic Insights: (Abedi-Firoozjah, Yousefi et al 2022)
Red cabbage extract is abundant in anthocyanins and polyphenols, which are hydrophilic compounds that enhance water solubility by forming hydrogen bonds with water molecules.
Polymer-Extract Interaction: The interaction between red cabbage extract and the base polymer could also alter the polymer network, making it more accessible to water molecules.
Functional packaging can be customized with red cabbage extract to meet specific needs for water resistance or solubility Lower concentrations of the extract are ideal for moisture-resistant packaging, whereas higher concentrations are more effective for applications that demand quick solubility.
Figure 24 Moisture contents and water solubility of films changing glycerol content
The addition of glycerol to the films leads to a gradual increase in moisture content, indicating that glycerol improves the film's moisture retention capabilities This observation aligns with glycerol's hygroscopic properties, which enable it to attract and hold water molecules from the surrounding environment.
The addition of glycerol to the films significantly enhances their water solubility, with a notable increase observed from 20% to 30% when glycerol content rises from 0.1 to 0.15 This trend indicates that glycerol improves the hydrophilic properties of the films, particularly at specific concentrations, leading to a stronger interaction with water.
Mechanistic Insights: (Basiak, Lenart et al.)
Plasticizing Effect: Glycerol acts as a plasticizer, reducing intermolecular forces within the polymer matrix and increasing the free volume, which enhances the film’s flexibility and water uptake capacity.
Hydrophilicity: Glycerol molecules contain multiple hydroxyl groups that can form hydrogen bonds with water molecules, increasing the overall solubility of the film in water.
Structural Changes: Incorporating glycerol disrupts the crystalline regions of the polymer matrix, creating a more amorphous structure that is easier to solubilize.
When selecting packaging materials, the glycerol content can be adjusted to meet specific needs for water resistance or solubility Films with lower glycerol levels are ideal for moisture-resistant applications, whereas those with higher glycerol content are more suitable for situations that demand quick solubility.
Water Vapor Permeability (WVP) measures a material's membrane capability to allow or block water vapor passage, typically expressed in g/m²·day This measurement is essential in assessing the barrier or permeable properties of membranes, particularly in applications such as food packaging The WVP of various films is demonstrated in the graph below.
Mechanical properties
The tensile strength (TS) of polymer films is essential for assessing their mechanical performance, with experiments examining the impact of Tragacanth gum substitution levels, anthocyanin extract ratios, and glycerol content Results indicate how these factors influence the films' mechanical properties, as illustrated in Figure 26 The graph demonstrates the effects of different concentrations of Tragacanth gum (Group 1), anthocyanin extract (Group 2), and glycerol (Group 3) on the tensile strength of the films.
Figure 26 Tensile strength lines of investigated films Group 1: Substitution Level of Tragacanth Gum
As the concentration of Karaya gum increases, the tensile strength (TS) of the samples decreases, with SP0G exhibiting the highest TS of approximately 70 MPa Modifications with hydrolysed Karaya gum ranging from 2.5g to 7.5g show a gradual decline in TS, yielding values of 58.46 MPa, 55.02 MPa, and 53.57 MPa, respectively Statistical analysis indicates that SP0G is significantly different from the other samples, while SP10G, SP20G, and SP30G demonstrate overlapping mechanical performance This reduction in tensile strength at higher concentrations of Karaya gum is likely due to the disruption of the polymer network's integrity, resulting in a less cohesive film structure and diminished interaction between polymer chains.
Group 2: Ratio of Red Cabbage Anthocyanin Extract
The inclusion of anthocyanin extract leads to a significant reduction in tensile strength (TS), with F0E measuring approximately 58 MPa, while F20E drops to around 14 MPa The low standard deviation across samples indicates consistent results, and statistical analysis reveals that F0E is significantly different from all other samples Notably, F5E, F10E, F15E, and F20E exhibit distinct reductions in TS This decrease in TS with higher anthocyanin content may be attributed to the plasticizing effect of the extract, resulting in a more flexible yet weaker film, highlighting a direct correlation between anthocyanin levels and film strength.
The study reveals that tensile strength (TS) declines as glycerol content increases, with F0G exhibiting the highest TS at approximately 83 MPa, while F4G displays the lowest at around 63 MPa Significant differences in mechanical strength are observed between F0G and F1G compared to F3G and F4G, highlighting a marked reduction in strength with elevated glycerol levels Additionally, the larger error bars for F3G and F4G indicate greater variability in these samples.
Glycerol serves as a plasticizer that enhances the flexibility of films; however, this improvement comes with a trade-off in tensile strength The inconsistency in mechanical properties observed in samples with higher glycerol content may be attributed to the uneven distribution of glycerol throughout the polymer matrix.
The study reveals that the type and concentration of additives greatly influence the tensile strength (TS) of polymer films Increased concentrations of Tragacanth gum and glycerol result in lower TS, likely due to diminished polymer interactions and enhanced flexibility Similarly, the inclusion of anthocyanin extract also contributes to reduced TS, possibly through its plasticizing effects These results underscore the necessity of optimizing additive concentrations to achieve a balance between mechanical performance and flexibility in polymer film applications.
Elongation at break (EAB) is an essential indicator of a film's flexibility and ductility, reflecting its capacity to stretch before failure The results, illustrated in Figure 27, demonstrate how different concentrations of Tragacanth gum (Group 1), anthocyanin extract (Group 2), and glycerol (Group 3) influence the EAB of the films.
The graph includes error bars representing the standard deviation and significance labels indicating statistically distinct groups.
Figure 27 Elongation at break of film samples Group 1: Substitution Level of karaya Gum
Increasing the concentration of Tragacanth gum leads to a significant decrease in elongation at break (EAB), with F0G showing the highest EAB at 83.21 ± 10.11%, indicating optimal flexibility Subsequent formulations exhibit lower EAB values: F1G at 74.80 ± 4.64%, F2G at 65.95 ± 3.24%, F3G at 62.63 ± 9.04%, and F4G at 62.99 ± 5.61% Statistical analysis confirms that F0G is significantly different from the other samples, while F3G and F4G demonstrate no significant difference between them The increased Tragacanth gum content appears to restrict flexibility due to enhanced rigidity in the polymer network The plateau effect observed in F3G and F4G indicates that further additions of gum do not significantly affect flexibility, underscoring a trade-off between flexibility and gum concentration.
Group 2: Ratio of Anthocyanin Extract
The study reveals a significant decline in elongation at break (EAB) as the ratio of anthocyanin extract increases, starting at 58.42 ± 1.32% for F0E and dropping to 14.10 ± 2.16% for F20E The low standard deviation values across samples indicate consistent results, with F0E showing a significant difference from all other samples As the anthocyanin extract ratio increases, there is a notable reduction in EAB, suggesting that the extract acts as a plasticizer, diminishing the film's stretchability under stress A strong correlation exists between higher anthocyanin content and reduced flexibility, indicating that increased anthocyanin levels lead to greater brittleness in the films.
The study reveals that an increase in glycerol content leads to a decrease in elongation at break (EAB), with SP0G exhibiting the highest EAB at 70.71 ± 11.41%, while SP30G shows the lowest at 53.57 ± 6.69% Statistical analysis indicates significant differences between SP0G and both SP10G and SP20G, although SP10G and SP20G show overlapping results The larger error bars for SP20G and SP30G suggest greater variability in these samples While glycerol enhances film flexibility, excessive levels can compromise structural integrity, ultimately reducing EAB This variability in films with higher glycerol content may stem from uneven glycerol distribution, highlighting the necessity to optimize glycerol levels to achieve a balance between flexibility and mechanical strength.
This study reveals that the type and concentration of additives significantly influence the elongation at break (EAB) of polymer films Higher levels of Tragacanth gum, glycerol, and anthocyanin extract typically result in decreased EAB, indicating a balance between desired mechanical properties and film flexibility Future research should focus on optimizing these additives to create films that fulfill specific mechanical and functional criteria for their intended applications.
Structural characteristics
FTIR analysis of films incorporating various additives, including karaya gum, red cabbage extract, and glycerol, reveals notable shifts in peak intensities and positions, reflecting modifications in the films' molecular structure and interactions (Perna, Capozzi et al 2020) These alterations indicate improved hydrogen bonding, enhanced plasticizing effects, and greater flexibility and solubility, making these films suitable for applications in biodegradable, active, and pH-sensitive smart packaging.
Figure 28 FTIR spectra of films with karaya gum change Observations:
O-H Stretching (3200-3600 cm^-1): Increased peak intensity with higher karaya gum content, indicating stronger hydrogen bonding due to the hydrophilic nature of karaya gum.
C-H Stretching (2800-3000 cm^-1): Slight changes in peak intensity and position, suggesting modifications in the aliphatic environment.
Fingerprint Region (800-1500 cm^-1): Significant changes in peak positions and intensities, indicating alterations in the molecular structure due to karaya gum.
C=O Stretching (1600-1750 cm^-1): Changes in this region suggest new interactions between karaya gum and the polymer matrix, potentially due to hydrogen bonding.
Figure 29 FTIR spectra of films with red cabbage extract change
O-H Stretching (3200-3600 cm^-1): Enhanced peak intensity with higher red cabbage extract, indicating increased hydrogen bonding.
C-H Stretching (2800-3000 cm^-1): Variations in peak intensity and position, suggesting changes in the aliphatic environment.
Fingerprint Region (800-1500 cm^-1): Changes in this region indicate molecular interactions between red cabbage extract and the polymer matrix.
Anthocyanin Peaks: Presence of peaks associated with anthocyanins, indicating successful incorporation of red cabbage extract.
Figure 30 FTIR spectra of films with glycerol change Observations:
O-H Stretching (3200-3600 cm^-1): Increased intensity with higher glycerol content, indicating enhanced hydrogen bonding.
C-H Stretching (2800-3000 cm^-1): Changes in this region suggest modifications in the aliphatic environment due to glycerol.
Fingerprint Region (800-1500 cm^-1): Significant changes in peak positions and intensities, indicating structural modifications due to glycerol.
Hydroxyl Groups: Peaks related to hydroxyl groups become more pronounced,reflecting glycerol’s impact on the polymer matrix.
Chemical properties
PVA-starch films containing 10% hydrolyzed karaya resin demonstrate excellent chemical properties ideal for pH-sensitive food packaging These films are biocompatible, flexible, and can adjust their color and antioxidant capacity through anthocyanin enrichment Recent research emphasizes their effectiveness in pH-responsive food packaging, showcasing improved oxidative stability and mechanisms for color change that are vital for monitoring food quality (Yan, Zhang et al 2022; Dong, Zhang et al 2023).
Figure 31 ABTS radical scavenging activity of films in two differents environment Comparison Between Environments:
The scavenging activity of red cabbage extract is notably greater in aqueous environments than in alcoholic ones at all concentrations, indicating that its active compounds, likely anthocyanins, are more effective and readily available in water.
The elevated radical scavenging activity associated with higher concentrations of red cabbage extract highlights its potential for antioxidant applications in aqueous environments, particularly in food packaging to inhibit oxidative degradation.
The reduced scavenging activity of the films suggests that, although they exhibit antioxidant properties in an alcoholic environment, their effectiveness is diminished This decrease may be attributed to the lower solubility or stability of anthocyanins when in alcohol.
Figure 32 Color transformation of polymer films following one-minute immersion in pH 2 to 12 buffer solutions
Color changes in polymer films under varying pH conditions reveal important information about their chemical stability and potential uses, including pH sensors The accompanying image displays the color transformations of different polymer films (F5E, F10E, F15E, F20E) after being immersed in buffer solutions with pH levels ranging from 2 to 12 for one minute.
The polymer films F5E, F10E, F15E, and F20E exhibit notable color transformations under different pH levels F5E maintains a light pink hue from pH 2 to 6, transitioning to greenish tones from pH 7 to 12 F10E presents a darker pink from pH 2 to 6, gradually shifting to green as pH increases F15E starts with a dark purple color that fades and transitions to green from pH 8 onwards In contrast, F20E displays a deep red or maroon hue at pH 2 to 6, with a pronounced shift to a more intense green at higher pH levels.
Polymer films demonstrate significant color changes in response to varying pH levels, showcasing their pH sensitivity attributed to components such as anthocyanins These films shift from pink or red at lower pH levels to green at higher pH levels, with a more noticeable transition occurring at lower pH in films with elevated anthocyanin content.
The concentration of anthocyanin extract in film compositions plays a crucial role in color transformations, with higher concentrations resulting in darker initial colors and more pronounced shifts For instance, F20E, which has the highest extract concentration, displays the deepest color at low pH and a significant transition to green at high pH In contrast, films with lower anthocyanin levels, such as F5E and F10E, show less intense color changes This demonstrates that a higher concentration of anthocyanin extract directly influences the film's color response to pH, leading to more notable transformations.
The observed color changes in the films indicate their potential use as pH indicators or sensors in diverse applications, including food packaging, biomedical devices, and environmental monitoring Their ability to undergo rapid color transformation within one minute highlights their suitability for real-time pH monitoring, providing immediate feedback on pH levels, which can significantly enhance safety and quality control across various industries.
In summary, polymer films exhibit notable pH sensitivity, as evidenced by their color transformation in varying pH buffer solutions, which is largely attributed to the anthocyanin extract Increased concentrations of anthocyanins lead to more pronounced and quicker color changes, highlighting a significant relationship between the extract's concentration and its responsiveness to pH variations.
The color parameters (L, a, b) of polymer films reveal their visual and chemical properties in response to varying pH levels Table x presents the average color parameters and standard deviations for films containing different anthocyanin extract concentrations (5g, 10g, 15g, and 20g) Notably, the lightness (L) values are generally high but decrease at lower pH levels, particularly in films with higher anthocyanin content, indicating darker colors As pH increases, L values rise, demonstrating a lightening effect The red/green parameter (a) transitions from high positive values at low pH to negative values at high pH, reflecting a shift from red to green tones Meanwhile, the yellow/blue parameter (b) starts negative and becomes positive with increasing pH, indicating a change from blue to yellow hues These color trends are more pronounced in films with higher anthocyanin content, suggesting that greater anthocyanin concentrations lead to more significant color transformations, enhancing the films' effectiveness as pH indicators in various applications.
Table 8 Color values (L,a,b) and total color difference ∆Ewith SD of F5E samples
L avg± SD a avg± SD b avg± SD ∆E avg± SD pH 2 79.03 ± 36.51 36.51 ± -5.53 -5.53 ± 37.54 37.54 ± 1.02 pH 3 77.35 ± 30.01 30.01 ± -5.06 -5.06 ± 32.25 32.25 ± 0.3 pH 4 78.13 ± 20.54 20.54 ± -1.03 -1.03 ± 23.96 23.96 ± 0.3 pH 5 78.24 ± 16.69 16.69 ± -6.98 -6.98 ± 20.92 20.92 ± 0.41 pH 6 87.1 ± 5.05 5.05 ± -6.02 -6.02 ± 6.62 6.62 ± 0.46 pH 7 89.03 ± 4.96 4.96 ± -8.08 -8.08 ± 6.34 6.34 ± 0.82 pH8 83.38 ± 3.21 3.21 ± -5.31 -5.31 ± 9.17 9.17 ± 0.46 pH 9 75.58 ± 4.59 4.59 ± -10.77 -10.77 ± 18.33 18.33 ± 3.23 pH 10 77.68 ± 1.69 1.69 ± -14.88 -14.88 ± 18.19 18.19 ± 1.59 pH 11 78.46 ± -5.91 -5.91 ± -1.58 -1.58 ± 15.85 15.85 ± 0.82 pH 12 87.58 ± -19.76 -19.76 ± 40.22 40.22 ± 49.35 49.35 ± 0.82
Table 9 Color values (L,a,b) and total color difference ∆Ewith SD of F10E samples
L avg± SD a avg± SD b avg± SD ∆Eavg± SD pH 2 62.93 ± 1.16 50.28 ± 1.51 -0.93 ± 0.46 57.06 ± 1.78 pH 3 80.08 ± 0.71 21.91 ± 2.97 -3.11 ± 0.63 23.93 ± 2.36 pH 4 78.74 ± 1.33 15.58 ± 1.56 -4.54 ± 0.39 22.01 ± 4.16 pH 5 72.58 ± 1.6 14.13 ± 1.06 -5.71 ± 0.98 23.53 ± 1.55 pH 6 74.32 ± 1.57 10.58 ± 0.82 -4.92 ± 0.56 20.2 ± 1.34 pH 7 75.99 ± 0.39 8.85 ± 1.21 -5.64 ± 2.27 18.15 ± 0.24 pH8 83.23 ± 0.4 5.04 ± 0.29 -7.04 ± 0.1 10.18 ± 0.28 pH 9 75.07 ± 1.15 7.39 ± 0.6 -15.2 ± 0.39 21.35 ± 1 pH 10 72.63 ± 0.63 -2.05 ± 3.58 -7.97 ± 1.52 20.69 ± 0.83 pH 11 69.79 ± 0.37 -15.12 ± 0.74 -3.46 ± 0.5 27.94 ± 0.19 pH 12 72.92 ± 0.99 -20.81 ± 0.42 43.19 ± 0.43 55.71 ± 0.51
Table 10 Color values (L,a,b) and total color difference ∆Ewith SD of F15E samples
L avg± SD a avg± SD b avg± SD ∆Eavg± SD pH 2 68.62 ± 2.44 46.95 ± 2.07 -3.21 ± 1.09 51.34 ± 2.58 pH 3 68.53 ± 2.83 27.11 ± 2.11 -4.37 ± 0.6 34.99 ± 3.32 pH 4 67.03 ± 1.02 18.43 ± 2.21 -2.66 ± 0.78 34.32 ± 3.91 pH 5 63.82 ± 2.53 21.39 ± 3.86 -1.18 ± 0.8 35.07 ± 2.75 pH 6 64.4 ± 1.3 11.32 ± 1.97 -6.03 ± 4.98 30.09 ± 1.79 pH 7 58.77 ± 0.9 13.27 ± 1.57 -6.8 ± 2.75 35.76 ± 1.34 pH8 51.6 ± 0.48 20.02 ± 2.03 -15.44 ± 0.26 46.17 ± 0.91 pH 9 55.55 ± 1.24 10.28 ± 0.18 -21.84 ± 1.49 41.77 ± 1.25 pH 10 64.33 ± 6.36 4.13 ± 5.06 -17.61 ± 5.07 31.62 ± 7.95 pH 11 64.68 ± 1.77 -10.43 ± 0.98 -8.94 ± 2.39 30.55 ± 1.51 pH 12 59.7 ± 1.13 -25.41 ± 3.67 44.56 ± 3.76 64.53 ± 3.28
Table 11 Color values (L,a,b) and total color difference ∆Ewith SD of F20E samples
L avg± SD a avg± SD b avg± SD ∆Eavg± SD pH 2 54.16 ± 0.37 60.21 ± 1.15 -2.47 ± 0.22 70.06 ± 1.15 pH 3 54.57 ± 0.49 41.86 ± 2.25 -4.98 ± 0.55 55.3 ± 1.92 pH 4 54.71 ± 0.54 27.74 ± 1.09 -11.15 ± 0.36 52.6 ± 5.24 pH 5 56.49 ± 0.6 12.72 ± 1.38 -1.18 ± 0.8 37.66 ± 0.79 pH 6 57.02 ± 1.44 10.48 ± 0.88 -8.65 ± 1.02 36.7 ± 1.41 pH 7 47.73 ± 0.62 14.36 ± 1.09 -10.08 ± 0.74 46.78 ± 0.7 pH8 52.78 ± 1.05 5.91 ± 0.56 -10.81 ± 1.3 40.33 ± 1.16 pH 9 57.01 ± 0.94 6.14 ± 0.15 -20.39 ± 1.17 39.16 ± 0.73 pH 10 54.04 ± 1.38 2.15 ± 1.35 -17.69 ± 1.71 40.64 ± 1.67 pH 11 51 ± 1.89 -10.08 ± 1.71 -8.72 ± 1.97 43.18 ± 1.66 pH 12 47.22 ± 0.93 -4.97 ± 1.15 28.98 ± 1.46 56.25 ± 1.49
Electrochemical printing on film
The article presents a series of surveys showcasing images of different film types It highlights the impact of varying concentrations of purple cabbage extract and printing durations on film quality Additionally, it features F10E films produced under diverse sources, illustrating the differences between normal polarity and reverse polarity systems.
(A) Changing the concentration of purple cabbage extract and printing time :
The left panel displays a grid of images illustrating the color transformation of films using varying concentrations of purple cabbage extract at 10, 20, and 30-second intervals With increased extract concentration and longer exposure times, the films demonstrate a significant color shift, transitioning from lighter shades to deeper, more saturated tones.
(B) F10E films under different sources, from left to right, with normal polarity and reverse polarity systems:
The right panel illustrates the color transformations in the F10E film when subjected to various light sources with normal and reverse polarity Images on the left exhibit a consistent greenish tint under normal polarity, while those on the right, reflecting reverse polarity, reveal a diverse color pattern with enhanced yellow and green regions, highlighting the film's distinct response to the polarity shift.
Impact of Purple Cabbage Extract Concentration and Printing Time (A) :
The color intensity of films enhances with increased concentrations of purple cabbage extract and prolonged exposure times, demonstrating that greater availability and interaction of anthocyanin pigments within the film matrix lead to more significant color changes.
Over intervals of 10, 20, and 30 seconds, a noticeable increase in color saturation highlights the time-dependent nature of color development in these films This indicates that both concentration and exposure time are essential for achieving optimal color intensity and uniformity.
Effect of Different Polarity Systems on F10E Films (B):
Under normal polarity conditions, F10E films exhibit a consistent greenish hue, indicating a stable interaction between anthocyanin pigments and the film matrix This uniformity in color suggests that the films respond reliably to standard polarity.
The reverse polarity system enhances color variability, prominently featuring yellow and green areas, indicating a differential response to polarity changes This phenomenon may arise from altered molecular interactions within the film The coexistence of yellow and green hues suggests intricate interactions that could be harnessed for advanced sensing applications, utilizing polarity to elicit specific colorimetric responses.
The findings from the panels reveal that polymer films are highly responsive to variations in anthocyanin extract concentration, printing duration, and external polarity conditions Films enriched with higher concentrations of purple cabbage extract and subjected to extended exposure times exhibit enhanced color intensity, making them ideal for applications that demand visible and long-lasting color changes Additionally, the differing responses of F10E films to polarity indicate promising uses in environments where polarity shifts serve as indicators of chemical changes Future research should delve into the mechanistic details of these interactions to improve the functional properties of these films for targeted industrial and scientific uses.
Table 12 The Lab* coefficients and ∆E of the film surveyed change with varying anthocyanin content and printing time
Film type L avg± SD a avg± SD b avg± SD ∆E avg± SD
CONCLUSION AND RECOMMENDATIONS
Research highlights the crucial role of three components—hydrolyzed karaya gum, red cabbage extract, and glycerol—in enhancing pH-sensitive polymer films Hydrolyzed karaya gum improves flexibility and uniformity, while red cabbage extract contributes pH sensitivity and antioxidant benefits Additionally, glycerol serves as a plasticizer, further enhancing flexibility and minimizing brittleness in the films.
The study investigated how red cabbage extract concentration, applied voltage, and printing duration affect electrochemical printing outcomes Results revealed that electrochemical reactions induce notable color changes: purple to green with the anode connected and purple to yellow with the cathode These alterations stem from water electrolysis, which modifies local pH levels Notably, the green hue is significantly influenced by hydrolyzed karaya gum, enhancing the variety of printed colors.
The introduction of new colors, green and yellow, enhances the aesthetic appeal of printed materials, moving beyond the traditional red and yellow This innovation not only boosts the visual attractiveness of films but also broadens their potential applications.
In summary, the pH-sensitive polymer films created in this research, along with advanced electrochemical printing technology, present significant potential for food monitoring and packaging applications By utilizing natural pigments for vibrant color printing and avoiding synthetic inks, these innovations promote safety and environmental sustainability The study highlights the capability of these films and printing methods to deliver dependable, real-time indicators of food quality, thereby enhancing food safety and minimizing waste.
This study identifies key limitations that future research should address, including the narrow range of polymer compositions analyzed, which focused on specific ratios of hydrolyzed karaya gum, red cabbage extract, and glycerol; a broader exploration could enhance understanding of film properties Furthermore, the technical survey of the electrochemical printing method was confined to limited variables, such as voltage and printing duration, suggesting that expanding these parameters may provide deeper insights into the printing process The application of the developed films for monitoring food spoilage was also limited, indicating a need for more extensive investigations across various food types and spoilage conditions to validate their practical utility Finally, the scalability of the electrochemical printing technique remains unexamined, raising questions about its feasibility for industrial-scale production Addressing these limitations in future studies could significantly improve the development and application of pH-sensitive polymer films.
Future research should explore diverse polymer compositions and blending ratios to enhance the properties of pH-sensitive films for various applications Comprehensive environmental testing is essential to evaluate the stability and performance of these films in real-world conditions Additionally, it is important to investigate the scalability of the electrochemical printing process for industrial use, aiming to create cost-effective and efficient large-scale production methods Assessing the long-term durability and effectiveness of pH-sensitive films, particularly their ability to retain pH sensitivity and structural integrity over time, will further confirm their practical utility and reliability Addressing these recommendations will significantly advance the development and application of these innovative materials.
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