Prepare the indigestible dextrin from rice starch by pyrolysis with different catalysts and characterise their product

INTRODUCTION

Introduction

In Vietnam, many rural areas still cultivate low-quality rice varieties due to their high yield, disease resistance, and adaptability to poor farming conditions While these varieties produce significant yields, their low quality adversely impacts the export potential, pricing, and reputation of Vietnamese rice To address this issue, diversifying rice products, particularly from low-quality varieties, presents a promising solution However, the lack of advanced processing technology limits the development of high-value products, with most rice-based offerings catering only to traditional Vietnamese culinary preferences Therefore, the introduction of innovative technology is essential for creating high-value rice products and achieving breakthroughs in the industry.

In Vietnam, the most successful new products derived from starch are "modified starches," which are created through chemical methods and enzymatic processes These modified starches primarily utilize starch from cassava, corn, potatoes, and wheat, with rice starch being notably absent It's important to note that due to the chemical denaturation processes—such as curing, grafting, or oxidation—these modified starches cannot be classified as food in the traditional sense; instead, they are used solely as additives, constituting only a certain percentage of food products.

Processing rice into resistant starch offers numerous health benefits, particularly for individuals with diabetes, obesity, high cholesterol, and those on weight loss diets Unlike regular starch, resistant starch is not broken down by the enzyme amylase and is not absorbed in the small intestine, which significantly lowers energy supply and prevents spikes in blood sugar levels This innovative dietary fiber surpasses traditional fibers in health advantages, making it a valuable addition to a balanced diet for everyone.

This fiber is heat resistant, acid stable, and remains unchanged as a food additive or when processed by digestive enzymes Additionally, it maintains a pleasant color and odor, does not alter the texture or taste of food, and requires no adjustments to existing recipes.

Dextrin pyrolysis is a prevalent method for starch denaturation, where thermal or acid catalytic hydrolysis transforms starch into oligosaccharides with lower molecular weights This process involves the breakdown of glycosidic bonds and the disruption of intermolecular bonds, resulting in dextrin that is highly soluble in water Additionally, the rearrangement of molecular links produces resistant dextrin, which is less digestible by human enzymes The structure of resistant dextrin features both straight and branched chains, with glucose units connected by various bonds, including α-1,2; α-1,3; β-1,2; β-1,3; and β-1,4, alongside the typical α-1,4 and α-1,6 bonds Acid-catalytic dextrinization occurs through an ionization process, where pyrolysis generates free radicals, with their concentration influenced by the temperature and duration of starch roasting.

Heat-generated dextrin, also referred to as resistant pyrodextrin, undergoes a four-step production process: pretreatment, pre-drying, pyrolysis, and quenching The critical phase that influences the final product is pyrolysis, where key parameters such as pH, humidity, temperature, and time play a vital role in determining the quality of the dextrin This study focuses on utilizing various catalysts, including acids, gamma rays, and activated carbon, to enhance the pyrolysis process.

Hydrochloric acid is primarily utilized in research and the industrial production of maltodextrin, while phosphoric acid is used to a lesser extent There is limited research on weak organic acids, resulting in incomplete efficacy data and a lack of comparative studies Specifically, information on the mixing ratio of hydrochloric acid as a catalyst for starch is scarce, with a common usage ratio of 0.1% often cited without specifying its base Additionally, irradiation can similarly disrupt starch structures, prompting the exploration of its application alongside acid catalysts to enhance process efficiency and product value Some global technologists have proposed using activated carbon as a catalyst for glucose pyrolysis, demonstrating significant effectiveness, particularly for glucose syrup.

3 proposed process is used industrially However, the use of activated carbon for starch pyrolysis has not been announced

From the above reasons, we performed the topic ―Prepare the indigestible dextrin from rice starch by pyrolysis with different catalysts and characterise their products”.

Research objectives

This study evaluates the impact of various catalysts on the pyrolysis reaction for producing pyro dextrin from rice starch It also investigates the resulting changes in the characteristics, properties, and structure of the product.

Clarifying the effect of acid catalyst on the pyrolysis to produce resistant dextrin from rice starch

Clarifying the effect of gamma-ray radiation treatment on the pyrolysis to produces resistant dextrin from rice starch

Determining the effect of activated carbon combined with irradiation on the pyrolysis of rice starch to produce resistant dextrin

Determining the composition, properties, characteristics and structure of pyrodextrin products generated from pyrolysis of rice starch with acid catalysts, irradiation and activated carbon

OVERVIEW OF RESEARCH ISSUES

Introduction of resistant dextrin

2.1.1 Starch, rice starch and modified starch

Starch is a vital agricultural product consumed globally, primarily composed of two polysaccharides: amylose and amylopectin Amylopectin features a highly branched structure due to its α-(1-4)- and α-(1-6)-glycosidic linkages, while amylose is mainly a straight-chain glucan Starch is abundant in various cereal grains, pulses, tubers, and some roots, existing as discrete starch granules The functionality of starch varies by botanical source, influenced by the ratios of amylose and amylopectin, their degrees of polymerization (DP), crystallinity, and mineral content, particularly phosphorus Amylopectin's molecular weight ranges from 1x10^7 to 1x10^9 Daltons, with peripheral chains having a DP of 12 to 24 glucose units, while primary branches have a DP of 42 to 119 In contrast, amylose has a lower molecular weight, between 1x10^5 and 1x10^6 Daltons, consisting of chains with up to 700 glucose units and minimal branching.

Figure 1 1 Chemical structure of starch

Crystalline powder is hydrolyzed by enzymes such as α-amylase, glucoamylase, and sucrase-isomaltase in the small intestine, allowing glucose to be absorbed in a free form However, not all dietary carbohydrates are fully digested and absorbed, as the digestibility of starch varies based on the enzymes involved and their ability to convert starch into glucose Consequently, starch sources are categorized into three types: fast digestion (FDS), slow digestion (SDS), and resistant starch (RS) While starch serves as a primary food source for humans, it also has significant applications across various industries, particularly in the food sector.

Rice starch, a natural polymeric carbohydrate, is the primary component of rice, existing as an insoluble white powder made up of amylose and amylopectin Unlike rice flour, rice starch has had most native proteins and lipids removed, with protein content in milled rice ranging from 4.5% to 15.9% and lipids at even lower levels The extraction of starch from rice primarily focuses on techniques that eliminate proteins, with the alkaline steeping method being widely used in industry and research This method ensures high recovery rates of rice starch with minimal residual protein and low damaged starch content, aiming for an isolated rice starch protein level of 0.5% or less.

Isolated rice starch contains not only proteins but also minor constituents such as lipids, phosphorus, and trace elements Non-waxy rice typically has 0.3%-0.4% bound lipids, whereas waxy rice starch has a lower lipid content of about 0.03% Research by Morrison et al (1993) identified the formation of an amylose-lipid complex in intact starch through solid-state nuclear magnetic resonance In non-waxy rice starch, the total lipid composition averages 32% free fatty acids and 68% lysophospholipids (LPLs), which include lysophosphatidyl choline (LPC) and lysophosphatidylethanolamine (LPE).

Phosphorus plays an extremely important role in starch functional properties, such as, paste clarity, viscosity consistency, and paste stability Phosphorus in starch is

In rice starch, phosphorus exists primarily in two forms: phospholipids and phosphate monoesters In nonwaxy rice, phosphorus predominantly appears as phospholipids, whereas in waxy rice, it is mainly found as starch phosphate monoesters.

Modified starch is produced using three main methods: physical, chemical, and enzyme-hydrolysis techniques Chemically modified starch is prevalent across various industries, particularly in food production, while physically modified and hydrolyzed starches are primarily utilized in food processing Chemically modified starches can be categorized into two types: starch and starch cutting replacements.

Starch modified by the enzyme: Application enzyme to handle starch essentially

There are two main categories in starch processing: resolution purposes and modified starch Enzyme resolution effectively reduces the molecular weight of starch into oligosaccharides or simple sugars, while modified starch alters the molecular weight without necessarily reducing it Enzymatic hydrolysis of starch is widely favored in Vietnam over chemical methods such as alkali or dilute acid hydrolysis, as it produces simple sugars like glucose, maltose, fructose, and high fructose corn syrup (HFCS), along with syrups characterized by their dextrose equivalent (DE).

Starch can be physically modified using various methods, including moist heat, microwave heating, irradiation, and high-pressure treatment (HHP) Gelatinization of starch occurs during heat treatment, which is influenced by the temperature and type of starch used Currently, the moist heat method is the preferred approach for producing resistant starch due to its efficiency and cost-effectiveness.

Resistant starch and its products are not digested in the small intestine, remaining undigested for up to 120 minutes before being fermented in the colon Research indicates that starch, particularly α-linear-glucan 1,4-D, undergoes transformation through amylose degeneration, resulting in a relatively low molecular weight of approximately 1.2 x 10^5 Da (Ratnayake & Jackson, 2007) Inert starch is currently classified into five distinct groups.

Starch synthesis occurs in the endosperm of grains, where starch particles are encased in protein and cell wall materials These structures create a physical barrier that hinders enzyme access, leading to reduced starch digestibility and lower blood glucose responses Foods rich in Group RS1 resistant starch include whole grain or coarse ground bread and pasta made from extruded hard wheat.

Group RS2 consists of unprocessed high-amylose potato starch, green banana, and ginkgo biloba, characterized by their polymorphic structures B or C These starches exhibit a high resistance to enzyme hydrolysis, making them a significant component of the inert starch group (RS2) (Jiang & Jane).

2013) However, after cooking, most of the starches, such as baked potatoes and cooked bananas, become easily digestible, causing starch gelatinization and disappearance of the B and C crystals

Group RS3 refers to a type of resistant starch that forms through the retrogradation process, which occurs when starch is cooked and subsequently cooled This form of resistant starch is known for its high resistance to heat and various curing agents.

Group RS4 refers to a category of chemically modified resistant starch that is not naturally occurring This diverse starch structure includes various forms such as ethers, esterified starches, and chemically treated starches designed to decrease digestibility Additionally, resistant maltodextrin, a soluble polysaccharide, is recognized as a type of resistant starch within this group.

When starch interacts with fat, amylose and amylopectin create helical structures with fatty acids and alcohols, forming single helix combinations This interaction prevents the binding and separation of starch by amylase, as linear starch circuits are trapped within the helical structure alongside fatty acids.

Resistant dextrin is commonly produced in foreign countries from corn starch, potatoes, and wheat through high-temperature and low-humidity methods, such as dry roasting or pyrolysis Similar to traditional dextrin, these resistant products consist of heterogeneous mixtures of D-glucose polymers, with molecular weights typically ranging from 3,500 to 6,000, depending on their quality Following production, the dextrin undergoes purification and concentration processes to achieve varying levels of purity.

Starch pyrolysis to create pyrodextrin with acid catalyst

2.2.1 Steps of starch pyrolysis with acid catalyst

The process of creating dextrin begins with treating starch with hydrochloric acid, followed by drying it to achieve a moisture content of only 4-5% This is followed by a roasting or pyrolysis treatment known as dextrination, resulting in products referred to as dextrin or more specifically, pyrodextrin The specific characteristics of the final product depend on various reaction conditions, including acid concentration, humidity, temperature, and curing time.

11 time), different products are available There are four main steps in the pyrodextrin process: pretreatment, pre-drying, pyrolysis, and cooling

Starch pretreatment is essential for lowering the pH during processing, particularly for producing golden dextrin, which requires a very low pH achieved by spraying starch with a dilute inorganic acid solution, such as hydrochloric acid, in mixers Gaseous hydrochloric acid is also effective for treating gelatinized starch British gum is produced without additives or with neutralizing salts like trisodium phosphate and ammonium bicarbonate After the addition of these additives, incubation times vary: approximately 30 minutes for white dextrin, up to 18 hours for British gum, and a few hours for yellow dextrin Uniform distribution of the acid in the starch is crucial to prevent issues during the subsequent heating process.

The drying step is essential for reducing water content, which accelerates the hydrolysis of starch polymers during heating, particularly at acidic pH levels, making it crucial for producing yellow dextrin In contrast, this step is less significant for white dextrin production, where hydrolysis is the primary reaction, and for British gums, where pyrolysis takes place at higher pH levels Additionally, the pre-drying process can be effectively combined with the pyrolysis step if the starch is heated slowly and continuously stirred.

Pyrolysis can be conducted using either vertical or horizontal mixers that are directly heated or heated with steam or oil Proper stirring during the process is crucial for achieving a homogeneous product, as it ensures even heat distribution Key variables affecting pyrolysis include acidity, temperature, rate of temperature increase, and incubation time For instance, white dextrin is typically produced at temperatures between 95°C and 120°C, yellow dextrin between 150°C and 180°C, and British gum between 170°C and 195°C Adjusting these variables can lead to the production of various types of pyrodextrin.

2001) In general, the increase in acidity causes pyrodextrin to have a lower viscosity while a higher temperature causes pyrodextrin to have a higher degree of branching

To halt pyrolysis once desired properties like color, viscosity, solubility, or indigestible fraction are achieved, starch can be quickly cooled using a mixer or conveyor with a cooling system, typically utilizing circulating water Additionally, if needed, the pH can be neutralized by blending pyrodextrin with an alkali, such as ammonium carbonate.

2.2.2 Pyrolysis reactions and the formation of indigestible fraction

Dextrination involves complex chemical changes that are not entirely understood, but it is believed to include three main types of reactions: hydrolysis, transglucosidation, and polymerization The significance of each reaction varies based on the specific type of pyrodextrin being produced.

The initial phase of dextrin pyrolysis involves the hydrolysis of α (1→4) glycosidic bonds, occurring during both pre-drying and the early stages of pyrolysis This hydrolysis of starch polymers leads to a decrease in product viscosity and an increase in the degree of reduction Notably, the hydrolysis reaction plays a crucial role in the production of white dextrin.

The transglucositisation process initiates under low water content in starch, leading to the formation of yellow dextrin and British gum During this reaction, starch chains are cleaved at (1→4) bonds, allowing them to interact with hydroxyl groups from different chains and create branching points This rearrangement can theoretically result in the formation of glucoside bonds, including (1→2), (1→3), (1→4), and (1→6), which may exist in either α or β-anomer configurations.

Theander & Westerlund (1987) reported the presence of O-α-glucopyranosyl-maltosan (1→4) and 1,6-anhydro-β-D-glucopyranose in pyrodextrin hydrolyzates derived from potato starch and wheat, produced using enzymes such as Termamyl and amyloglucosidase They suggested that 1,6-anhydro-β-D-glucose, also known as levoglucosan, was present as the terminal unit in these pyrodextrins.

Recent studies on cycloheptaamylose pyrolysis have revealed its potential as a model for starch, conducted at high temperatures (250-1000ºC) and varying pressures, including vacuum conditions This process yields a diverse range of volatile and non-volatile compounds, while low-temperature pyrolysis offers insights into reactions occurring during high-temperature metabolism Notably, Lowary & Richards identified 1,6-anhydro-β-D-glucose as the primary product (38-50%) from vacuum pyrolysis of cycloheptaamylose at temperatures of 280, 300, and 320ºC They proposed a reaction mechanism involving the formation of a glucosyl cation through heterogeneous dissociation of the glucoside bond, leading to the creation of a seven-member open-chain oligosaccharide This cation is then stabilized by an internal attack from molecule O6, resulting in an oligosaccharide with anhydro-glucose, followed by the release of glucose anhydro through subsequent glucoside segments, generating another glucose cation.

Lowary & Richards (1991) proposed a mechanism for high-temperature pyrodextrin involving the cleavage of starch chains, resulting in a cationic glucosyl at one end The stability of this cationic glucosyl is influenced by transglucosylation chemistry, which involves the attack of associated molecules rather than an endomolecular attack The addition of the glucosyl cation to the hydroxyl groups of adjacent starch chains creates branching points Additionally, pyrolysis at temperatures lower than 171ºC and under atmospheric pressure, conditions resembling those of pyrodextrin, promotes metabolic reactions through intermolecular addition.

Evidence suggests that the production of yellow dextrin leads to a slight increase in viscosity and a decrease in the removal of pyrodextrin, particularly when a prolonged lag time is employed This phenomenon is attributed to the re-polymerization of glucose or oligosaccharides into larger molecules The high temperatures and acidic conditions necessary for yellow dextrin production facilitate the polymerization of glucose.

Starch pyrolysis to create pyrodextrin with gamma radiation as catalyst

Author Zhu from the University of Auckland, New Zealand, recently published a review in the journal "Food Hydrocolloids" titled "Impact of γ-irradiation on structure, physicochemical properties, and applications of starch." This review explores how γ-irradiation affects the structural and physicochemical characteristics of starch, highlighting its various applications in the food industry.

Irradiation of starch generates free radicals that interact with water and starch components, leading to changes in molecular structure and particle size This process reduces the size of amylose and amylopectin while increasing the ratio of unit chains with degrees of polymerization (DP) ranging from 6 to 12 Low doses of irradiation do not significantly affect grain morphology, but higher doses cause visible damage to starch particles Although the polymorph type of starch remains largely unchanged, the degree of crystallization tends to decrease Gamma-ray exposure enhances water solubility and amylose leaching while reducing starch granular swelling, which results in decreased viscosity during liquefaction Additionally, irradiation can influence the temperature and enthalpy change of the gelatinization process, as measured by differential scanning calorimetry (DSC), and may alter the enzyme sensitivity of gamma-irradiated starch.

Gamma irradiation, when combined with various agents like acids and peroxides, enhances the efficiency of chemical reactions, yet there is limited knowledge about its interaction with physical agents such as heat treatment Irradiated starches have proven to be versatile, leading to the production of nanoparticles, thermoplastics, and sizing agents utilized in the textile industry.

To enhance the utilization of gamma irradiation in starch applications, it is essential to focus on several key areas: Firstly, important test parameters such as starch moisture, dose, and irradiation dose rate must be prioritized Secondly, a deeper exploration of the structural aspects of starch is necessary to understand the molecular basis for changes and enzyme sensitivity following irradiation Thirdly, investigating the potential industrial applications of higher dose starch irradiation, particularly doses exceeding 100 kGy, could yield significant benefits Lastly, a comprehensive examination of the chemical, physical, and enzymatic properties of irradiated starch is crucial for optimizing its applications across various industries.

15 treatments need to be combined with irradiation with different treatment sequences to give a wider range of properties and to improve reaction efficiency

The selection of a dose range between 5-50 kGy is primarily intended for applications within the food industry, while such high doses are more relevant for non-food applications.

2.3.2 The effect of irradiation treatment on the content of resistant starch

Gamma irradiation is an effective physical method for modifying starch properties, offering benefits such as minimal temperature increase during processing, rapid sample preparation, and independence from catalysts (Gani et al., 2014) Typically conducted using a Co-60 gamma-ray source, the dose rate ranges from 0.4 to 10 kGy/h While starch samples can be irradiated with doses up to 100 kGy, current regulations limit food irradiation to 10 kGy in Canada and the European Union, and to 30 kGy in the United States as of 2013 for standard consumer products.

The process of irradiation to create resistant starch is intricate and not fully understood, primarily because it involves oxidation caused by free radicals generated from the carboxyl groups in starch Additionally, the formation of beta (1-4) linkages plays a significant role in this transformation.

3) and beta (1-4) bonds in starch due to transglycozitization (Rombo et al.,

Starch containing beta bonds remains undigested, while the formation of curing among gluco-polymer chains with a degree of polymerization (DP) greater than 25 is enhanced by the increased number of vessels resulting from amylopectin fracture Additionally, the crystallinity of type V rises due to the development of amylo-lipid complexes.

International studies highlight that irradiation technology offers a significant advantage in food fiber production compared to other methods such as chemical, enzymatic, and physical processes This technology not only shortens production time but also eliminates the issue of residual matter.

Irradiation offers significant advantages for increasing resistant starch compared to other methods, primarily due to its rapid processing time Unlike hydroxypropylation, which takes approximately 40 hours, or cyclic autoclave/degeneration that can range from 24 to 216 hours, irradiation can achieve fast treatment rates with high dose rates of up to 10 kGy/h (Dundar & Gocmen, 2013; Yoon et al.).

2010) In addition, the use of irradiation has the added benefit of leaving no harmful residues in starch, compared to many chemical methods Rice starch with high (8%),

Irradiation at 5 kGy resulted in 16 samples containing medium (3.8%) and low (2%) levels of endogenous inert starch The sample with high resistant starch (8%) exhibited the most significant increase at 2 kGy, while the other two samples retained the highest levels of inert starch after being irradiated at 4 kGy.

Lower dose rate irradiation results in reduced decomposition of amylose and less amylopectin breakage, which enhances the crystallinity and functionality of resistant starch (Chung & Liu, 2009) In a comparison of dose rates at 0.40, 0.67, and 2 kGy/h, the 0.40 kGy/h rate yielded the highest resistant starch content at 24.7%, while higher rates produced lower levels of 23.0% and 22.2%, respectively Additionally, research indicates that cross-linked corn starch STMP/STPP also exhibits significant effects from irradiation, with natural samples showing the highest resistant starch levels post-irradiation.

40 kGy at a dose of 10 kGy/h of 30.4%, while samples using 5% or 10% STMP/STPP had the highest at 10 and 20 kGy, sequence 57.2% and 67.3%

Irradiated rice starch and other starches can enhance the content of indigestible fractions The underlying mechanisms of this process remain unclear, particularly regarding the formation of resistant starches Various types of resistant starch can be produced through different irradiation mechanisms, with the effectiveness influenced by factors such as irradiation dose, dose rate, starch moisture, and the specific characteristics and impurities of each starch.

Currently, there are no published results on the synergistic effects of gamma irradiation combined with pyrolysis for the production of pyrodextrose This process not only generates resistant starch but also serves as a catalyst, effectively replacing acids in the pyrolysis reaction.

Starch pyrolysis to create pyrodextrin with other catalysts

Hamaguchi et al (2014) introduced a novel method for producing water-soluble resistant polysaccharides by heating glucose at 180°C with activated carbon This approach not only serves as a catalytic aid for polycondensation but also facilitates easy separation from reagents and enhances product coloration The study revealed significant variations in results when comparing different catalysts during the pyrolysis of glucose solutions under identical conditions Notably, the indigestible fraction of the sample was produced without the use of catalysts.

In a study, it was found that only 55.4% of the sample utilized 2% activated carbon (w/w), while 85.8% of the sample employed a catalytic acid, specifically HCl at 0.2% (w/w) Notably, the solution treated with acid catalysis exhibited a significantly darker color compared to the lighter solution produced using activated carbon as a catalyst.

Prior to refinement, over 80% of the reaction mixture consisted of indigestible content Following hydrolysis catalyzed by α-amylase and glucoamylase, and subsequent fractionation through ion exchange chromatography, the total fiber content increased to 99.7% This indigestible fraction, known as resistant glucan, exhibits minimal degradation by upper digestive enzymes, akin to the digestibility of polydextrose Structural analysis via methylation and NMR revealed that resistant glucan possesses a highly branched structure with various linkages, including α- and β-1,2; 1,3; 1,4; and 1,6- On an industrial scale, glucan antibodies were derived from glucose syrup (DE 86) through heating with activated charcoal, enzymatic hydrolysis, purification, segment separation, and spray drying.

Currently, there is a lack of comprehensive studies on the impact of activated carbon during the pyrolysis process, both globally and in Vietnam Most research has concentrated on the decolorization capabilities of activated carbon in hydrolysis rather than its catalytic effects in pyrolysis Consequently, there is a need for research that examines the catalytic role of activated carbon when introduced at the onset of pyrolysis, particularly regarding its influence on the production of resistant dextrin.

Characteristics of resistant pyrodextrin and typical analytical techniques

The functional properties of pyrodextrin are influenced by changes in molecular size, branching ability, and glucosidic bonding A reduction in molecular size leads to decreased viscosity, allowing for pyrodextrin synthesis at higher water concentrations compared to natural starch Additionally, increased branching enhances solution stability, enabling pyrodextrin to dissolve in cold water and reducing the risk of retrogradation, as demonstrated by Bernadine Brimhall in 1944 with commercial pyrodextrin made without an acid catalyst Furthermore, the formation of non-starch bonds can negatively affect in vitro digestibility.

18 pyroconverted starch (Laurentin et al., 2003) Therefore, pyrodextrin is soluble in cold water, develops low or no viscosity in solution, and is partially resistant to digestion

Pyrodextrin undergoes significant chemical changes that result in a free-flowing, colored powder, ranging from white or light brown to dark brown, while maintaining low moisture levels of typically 1-4% These changes lead to a notable alteration in grain morphology and a relatively low reduction capacity, although it is higher compared to natural starch.

Thermogravimetry (TGA) is a technique that measures the mass of a sample as it undergoes a controlled temperature program in a specific atmosphere, providing insights into thermal stability and decomposition, particularly for starch-based materials The derivative thermogravimetry (DTG) offers a sensitive analysis, revealing the relative rates of volatilization and polymer decomposition, with peak maxima indicating the highest mass loss rates Each weight loss step corresponds to a peak in the differential thermal analysis (DTA) curve, representing distinct events within specific temperature ranges, though complex processes may require further manipulation or deconvolution of overlapping peaks.

Dynamic Thermogravimetric (DTG) analysis is essential for studying starch degradation, as it effectively differentiates overlapping mass loss events and identifies the shapes and maxima of these processes Additionally, DTG provides valuable insights into minor mass loss steps This technique is commonly employed to investigate the thermal degradation kinetics of polysaccharides, offering reliable data on activation energy, exponential factors, and overall reaction orders.

2.5.2.2 TGA-FTIR and TGA-MS

The TGA offers a quantitative assessment of mass loss from a sample but lacks details on the nature of the lost products Understanding these chemicals during thermal decomposition is crucial for investigating decomposition mechanisms By integrating a gas analyzer or detector, such as mass spectrometry (MS) or Fourier-transform infrared spectroscopy (FTIR), with TGA, researchers can analyze the evolved gases for more comprehensive insights.

Evolved gas analysis (EGA) provides essential insights for polymer characterization, including the detection of moisture and solvent loss from samples, as well as the study of thermal stability processes and reaction mechanisms.

(Darribere, 2010) is a method used to study the gas evolved from a heated sample that undergoes decomposition or desorption

Gel permeation chromatography (GPC), also known as size exclusion chromatography (SEC), is widely used to analyze the size and molecular weight distribution of starch However, accurately characterizing the molecular size distribution of starch polymers through GPC remains a challenging task Numerous reviews, including those by Gaborieau & Castignolles (2011), have raised concerns about the effectiveness of existing size separation technologies in providing size distributions that are suitable for understanding the macromolecular structure of starch, particularly in the case of highly branched varieties like waxy starch.

Electron paramagnetic resonance (EPR), also known as electron spin resonance (ESR) spectroscopy, is a valuable technique for analyzing chemical species with unpaired electrons, including organic and inorganic free radicals and transition metal ion complexes During thermal processing, such as conventional heating, microwaves, extrusion, and irradiation, radicals in starch are generated EPR effectively studies radical processes that occur when starch is heated within the temperature range of 150–250°C.

MATERIALS AND METHODS OF RESEARCH

Research subjects

Rice starch TB1 (M1) is derived from the IR50404 rice variety provided by Hoa Phat Company This starch contains 82.3% carbohydrates, 5.2% protein, and has a pH level of 4.16 During irradiation experiments, the IR50404 rice was further purified to achieve a protein content of less than 1% and a lipid content of less than 0.5%.

- Rice starch TB2 (M2): Provided by the Company in Ho Chi Minh City, has carbohydrate, protein and pH content of 86.2%, 2.4% and pH 3.86 respectively

- Rice starch TB3 (M3): TB1 starch is refined in the laboratory, with carbohydrate, protein and pH 85.7%, 2.8% and pH 7.63 respectively

- Actived carbon, symbol MD-1 provided by Minh Duong Food Joint Stock Company Main parameters: fine powder, black color, iodine index: 900-1000 mg/g, pH: 8 ’ 9.

Chemicals

- Kit for determining 3 sugars: Mega-Calc TM: Maltose / Sucrose / D-glucose (K-MASUG) (Novozymes A/S, Denmark)

- Kit for determination of total dietary fiber TDF: Total Dietary Fiber Kit (K- TDFR-100A / K-TDFR-200A 04/17) (Novozymes A/S, Denmark)

- Kit K-GLUC để xác định đường D-glucose (GOPOD Format) (Novozymes A/S, Denmark)

- Enzymes (amylase, amyloglucosidase, protein: (Novozymes A/S, Denmark)

- Chemical analysis of protein, lipid, amylose, inert starch,….

Equipment and tools

- Croma meter (CR-400 Konica Minota colorimeter)

- pH meter (portable and portable)

- Oven of all kinds (Dryer JSOF-100, Memmert)

- Vacuum rotary evaporator (Heidolph, Germany);

- Mixing - drying - roasting equipment, pilot scale (Vietnam) (5-8 kg / batch)

Experiment design

3.4.1 Experiment about the effects of different acid on pyrolysis

The experiment aims to identify the safest acid to act as an effective catalyst for pyrolysis, focusing on producing dextrin with a high indigestible fraction, minimal time, and low color variation Four acid solutions are prepared: acetic acid (CH3COOH), citric acid (C6H8O7), hydrochloric acid (HCl), and lactic acid (CH3CH(OH)COOH), each at a concentration of 0.33 M A mixture of 100 g of rice starch and 10 ml of each acid solution is blended using a mixing machine The samples are then placed in sealed plastic containers and incubated overnight before transferring 20 g of each sample into Petri dishes for further analysis.

The samples were dried to remove moisture at 105°C for 60 minutes, followed by pyrolysis at 170°C for 120 minutes After the pyrolysis process, the samples were rapidly cooled to room temperature, sealed in airtight bags, and stored for further analysis Each recipe was prepared with three independent samples, resulting in a total of 12 Petri dishes.

3.4.2 Experiment about the effect of concentration of HCl on pyrolysis

The experiment aims to identify the optimal concentration of hydrochloric acid (HCl) as a catalyst for the pyrolysis process Hydrochloric acid solutions at concentrations of 1.00%, 1.5%, and 1.75% are prepared and mixed with dry starch to create samples with pH levels of 2.1, 2.3, 2.5, and 2.7 After thorough mixing, the samples are incubated for 10-15 hours in sealed plastic containers at room temperature Subsequently, 20 g of each sample is placed in Petri dishes to dry, with lids removed to eliminate moisture at 105 ºC for 60 minutes, followed by pyrolysis at 170°C until the starch color reaches 60-62% This process is repeated three times, with analytical criteria focused on whiteness and inulin dietary fiber (IDF).

3.4.3 Experiment about the effect of pyrolysis temperature

The objective of Experiment 3 is to assess the impact of temperature on the quality of pyrolysis-resistant dextrin Starch samples M1 (TB1) and M2 (TB2) will be utilized, with drying conducted at 105ºC to achieve a moisture content of 4-5% A mixture of 100 g of starch combined with 1% acid will be incubated overnight Subsequently, 20 g from each formula will be placed in petri dishes for drying without a lid to eliminate moisture.

The heat treatment division conducted experiments over a span of 60 minutes, followed by a 120-minute heating period at varying temperatures of 140, 150, 160, 170, and 180°C After heating, the samples were rapidly cooled to room temperature, then bagged and preserved for analysis The analytical criteria assessed included whiteness, IDF content, and solubility, with each experiment being repeated three times for consistency.

3.4.4 Experiment about the effect of pyrolysis time

The aim of the experiment is to be selected out of about the optimum time for the pyrolysis process to produce resistant dextrin The procedure is similar to experiment

3 Using 100 g of starch with 4% moisture, mixing with 10 ml of 1% HCl acid solution Incubate the sample overnight in a plastic container, then take 20 g of each recipe into a Petri dish, and dry to remove moisture and open the lid at 105 C for 60 minutes Cover and pyrolysis at 170ºC according to 4 different formulas of pyrolysis

The samples were subjected to heating durations of 60, 90, 120, and 150 minutes, after which they were allowed to cool to room temperature Subsequently, the samples were bagged and stored in a vacuum desiccator Key analytical parameters measured included dextrin whiteness, IDF content, and solubility, with each experiment being repeated three times to ensure reliability of results.

3.4.5 Experiment about the effects of gamma radiation in different doses

Starch M1, which is re-purified with less than 1% protein and less than 0.3% lipid, has a moisture content of 5% A total of 400 g of this starch is placed in a rectangular plastic container (750 ml, dimensions: 17 x 10 x 5 cm) Each irradiation treatment consists of three containers, subjected to absorbed doses of 5, 10, 20, 30, 40, and 50 kGy at a dose rate of 5 kGy/h The irradiation process is conducted at the Hanoi Irradiation Center using a Cobalt-60 gamma radiation source.

The study measured the irradiation dose of 100 kCi using an ECB dosimeter, revealing a discrepancy of less than 10% between the theoretical and actual doses The evaluation of irradiation effects on starch was based on several criteria relevant to pyrodextrin applications, including the indigestible fraction (IDF), changes in starch whiteness measured by a Kett C-300 powder whiteness tester, and color deviation (ΔE) assessed with a CR-400 Konica Minolta colorimeter Additionally, the water solubility of starch was analyzed at both 25°C and 70°C, along with pH levels.

3.4.6 Experiment about the effect of gamma radiation in different dose rates

The experiment aims to identify the optimal irradiation dose rate for producing pyrodextrin with the highest indigestible fraction (IDF) The irradiation was conducted at a dose of 10 kGy, using three different dose rates: 1 kGy/h, 2 kGy/h, and 3 kGy/h Evaluation criteria included measuring the indigestible fraction along with additional assessments.

3.4.7 Experiment about the effect of gamma irradiation combined with non- acidic catalysist pyrolysis

Following irradiation as outlined in experiment 5, the irradiated starch was distributed into Petri dishes (Φ12 cm) for pyrolysis at 170°C for 300 minutes, with each recipe consisting of four plates To ensure uniform heat distribution, the samples were carefully arranged in the oven After the drying process, the samples were quickly cooled in a refrigerator The evaluation of irradiation effects was conducted based on criteria including color change measured by a Kett C-300 whiteness tester, water solubility at 30°C, and the content of insoluble dietary fiber (IDF).

3.4.8 Experiment about the effect of gamma irradiation combined with HCl catalyst pyrolysis

The study utilizes purified rice starch with 5% moisture, subjected to gamma irradiation doses of 0, 10, and 30 kGy A hydrochloric acid solution with varying concentrations (0.25, 0.5, 0.75, and 1.0) is added to the starch at a 1:10 ratio (v/w), mixed thoroughly, and incubated for five hours The mixture is then dried to achieve a moisture content of 4-5% before undergoing pyrolysis at temperatures ranging from 150 to 170°C Key evaluation criteria include the pH level prior to pyrolysis (composted acid), the roasting time required to reach a brightness of 60%, whiteness, color difference (ΔE), and the indigestible fraction.

3.4.9 Experiment about the effect of the rate of activated carbon added

Use 10 kGy irradiated starch with a moisture content of 5% Add activated carbon in the ratio of: 0, 1, 2, 3, 4, 5, each with 5 Petri dishes (30 dishes) Use 0.5% HCl solution to mix samples at the rate of 0,05% by weight of powder Incubate for 5 h and then roast at 170ºC until whiteness of the formula without charcoal reaches 65% whiteness The experiment was repeated 3 times Measurements to evaluate quality changes were similar to previous experiments

3.4.10 Experiment about the effect of pyrolysis time with activated carbon catalyst

In this study, we investigated the optimal ratio of activated carbon for examining the impact of pyrolysis time on pyrodextrin production Using 5% moisture-irradiated starch, activated carbon was added in five distinct formulations A 0.5% HCl solution was mixed with the samples at a concentration of 0.05% by weight of the powder The samples were incubated for five hours and then roasted at 170ºC, with removals at three different time intervals The experiment was conducted three times to ensure reliability, and the quality changes were assessed using methods consistent with previous studies.

3.4.11 Experimetn about verification of pyrolysis at pilot scale and final product charactification

The experiment aimed to evaluate the quality of digestible pyrodextrin produced from three pilot batches, each weighing 8 kg, and compare it with the quality of the product generated at a smaller laboratory scale Refined M1 starch was utilized in both the laboratory pyrolysis treatment and the pilot scale process The pilot scale involved processing 8 kg of starch using roasting equipment specifically designed and manufactured by KC.05.20 / 06-20, following the same procedures as in the small-scale production All starch samples from both scales exhibited consistent quality.

25 acidification (pH 2.5), treatment temperature of 160 o C Processing times are recorded until the color reaches 60-65% whiteness.

Analytical methods

The IDF content was determined using an improved method based on Englyst & Hudson (1996) Initially, 1 gram of the pyrodextrin sample was weighed and mixed with 50 ml of 0.08M phosphate buffer at pH 6.0, followed by the addition of 0.1 ml of the heat-resistant enzyme α-amylase (Termamyl 120L, Novo, Laboratories, Inc., USA) The mixture was incubated at 95°C for 30 minutes, then cooled to room temperature, and the pH was adjusted to 7.5 ± 0.1 using approximately 10 ml of 0.275 M NaOH Next, 0.5 ml of protease solution was added, and the reaction continued at 60°C for another 30 minutes After cooling, the pH was adjusted to 4.5 using about 10 ml of 0.325 M HCl Finally, 0.3 ml of amyloglycosidase was added, and the mixture was heated to 90°C for further analysis.

To terminate the reaction, allow 15 minutes before filtering the mixture and diluting it to 100 mL with distilled water The glucose content is then measured using pyranose-oxidase with the K-GLUC kit (GOPOD Format) from Novozymes, Denmark Additionally, the indigestible fraction (IDF) is calculated using a specific formula.

The TDF content of pyrodextrin or starch was analyzed using the AOAC 2001.03 method, incorporating enhancements in sugar determination through HPLC For this analysis, the K-MASUG kit from Novozymes, Denmark, was utilized to measure total sugars, specifically DP1 and DP2, which include maltose, sucrose, and glucose.

Color differences are evaluated using the Hunter system with a photoelectric colorimeter (CR-300 Minota, Tokyo, Japan) This system categorizes colors based on three key attributes: L, which ranges from 100 for white to 0 for black; a, where positive values indicate red and negative values indicate blue; and b, which measures yellow.

= positive, blue = negative) Color difference (ΔE) were measured using the color of

26 rice strach untreated (natural origin) as a standard The relationship between the three color properties (L , a and b) is described by the equation:

To measure the color of an aqueous solution, prepare a 10% pyrodextrin solution, equivalent to a Brix of 10% After filtering through pre-filter paper, measure the optical density (OD) at 420 nm and 720 nm using a 1 cm thick quartz cuvet The color of translation is determined by taking the absolute difference of the two OD values and multiplying by 10 (Maeda, Shimada & Katta, 2015).

Following the methodology outlined by Anderson et al., 40 ml of a 1% starch solution (w/v, db) was added to a pre-weighed 50 ml centrifuge tube The tubes were stirred continuously and placed in a water bath for 30 minutes at varying temperatures of 60, 70, 80, or 90 °C, with the starch temperature monitored using a thermometer After the designated time, the tubes were removed from the water bath and centrifuged at 2121g for 15 minutes The resulting gel was then weighed (W2), and the water absorption was calculated as the gel mass (g) per gram of dry sample.

The Sedit and Salunkhe method involves taking 40 ml of 1% starch solution in a pre-weighed 50 ml centrifuge tube, which is then placed in a water bath at temperatures of 60, 70, 80, or 90°C for 30 minutes while stirring continuously The temperature is monitored using a thermometer in each tube After the incubation period, the tubes are removed from the water bath, stirring is stopped, and the tubes are dried before centrifugation at 2121g for 15 minutes The supernatant is decanted, and 10 ml of it is placed in a crucible to dry at 120°C for 4 hours until a constant mass is achieved Finally, the crucibles are weighed to calculate the dry matter fraction and solubility using specified formulas.

3.5.6 pH of starch and dextrin

In experiments, the pH of starch was assessed by mixing 25 g of dry starch or dextrin with 50 ml of deionized water, creating a 1:2 (w/v) ratio Additionally, the pH value of starch was measured according to TCVN 10546:2004 for tapioca starch, which specifies a 10% (w/v) starch solution for pH determination.

3.5.7 Protein and crude fat content

Protein content analysis follows TCVN 4328:2007 standards, utilizing a semi-automatic protein distillate for crude protein quantification via the Kjeldahl method This method comprises three key phases: sample digestion, distillation, and titration The protein content is determined by multiplying the nitrogen content by a conversion factor of 5.67.

The fat content analysis follows TCVN 4331:2001 standards, utilizing the VELP SER 148/6 device for semi-automatic determination of total fat in test samples This method relies on the complete solubility of fat in an organic solvent, which extracts the fat from the sample After the solvent is evaporated, the remaining fat is weighed to calculate the fat content as a percentage of the sample's dry mass prior to extraction.

3.5.8 Investigation with scanning electron microscope (SEM)

The scanning electron microscope (SEM) analysis was conducted at the Institute of Materials Science, Vietnam Academy of Science and Technology, utilizing a Jeol JSM 6490 JED with a coaster tray (JFC 1200, JEOL, Japan) This study examined whole rice starch, degenerated starch, and starch hydrolyzed by pullulan enzymes, following the methodology outlined by Atichokudomchai et al (2000) Prior to analysis, all samples were dried to achieve a moisture content of at least 4% The dry samples were applied onto double-sided tape on the stand, with excess material removed, and then coated with gold for 150 seconds before being placed in the SEM sample chamber The samples were tested at magnifications of X 2,500 and X 6,000, utilizing specific accelerating potentials.

3.5.9 Investigation by X-ray diffraction measurement (XRD)

X-ray diffraction images of rice starch samples (original, heat treatment, inert starch) were determined by SIEMENS D500 equipment (Germany) at Institute of Materials Science, Vietnam Academy of Science and Technology The procedure was conducted according to Cheetham & Tao (1998) Take approximately 5 g of sample, seal it in a rectangular silicon box and spread the sample to a smooth surface and place it in the sample holder Exposure to X-beam XRD conditions with monochromatic

Cu-K2 rays with a wavelength of 0.15405 nm were generated in closed tubes at 40 kV and 40 mA Diffraction images were collected using a 2Ɵ scan angle ranging from 10° to 60° with a step size of 0.05° and a counting duration of 2 seconds The data analysis was performed using the MDI Jade 6.5 software (Japan) The crystallization degree of the starch sample was determined by calculating the ratio of the crystallization area to the total area within the 10° to 45° angle range (Cairn et al., 1997).

3.5.10 Fourier transform infrared spectrometry (FTIR)

FTIR results were determined by Institute of Tropical Technology - Vietnam Academy of Science and Technology

3.5.11 Differential scanning calorimetry (DSC/DTA)

Differential scanning calorimetry (DSC), differential thermal analysis (DTA), and thermal gravimetric analysis (TGA) are conducted using the Labsys Evo S60 / 58988 equipment in the Heat Analysis Department at the Institute of Chemistry, Vietnam Academy of Science and Technology The analysis is performed on samples in a nitrogen atmosphere, with a heating rate of 5 to 10°C per minute, starting from room temperature.

The gelatinization and pasting properties of rice starch are assessed using a Rapid Visco Analyzer (RVA) following the AACC 61-02 methodology To conduct the analysis, 3 g of rice starch with 13.5% moisture is dissolved in 25 g of distilled water within an aluminum tube and placed in the RVA The mixture is stirred at 900 rpm for the initial 10 seconds to ensure proper mixing.

RESULTS AND DISCUSSION

Acid catalytic effect on pyrolysis to create resistant dextrin from rice starch

In a study on the pyrolysis of rice starch, four acids—acetic, citric, hydrochloric, and lactic—were employed as catalysts, all at a concentration of 0.33M However, their percentage concentrations varied, measuring 1.89%, 3.82%, 1.00%, and 2.46%, respectively The pyrolysis process was conducted at 170 ºC for 120 minutes, and the results detailing key quality parameters of the resulting dextrin products are illustrated in Figure 4-1.

Figure 4.1 Effect of different acids as catalyst in pyrolysis to produce resistant dextrin from rice starch M1

CT1, CT2, CT3, and CT4 represent different types of starches catalyzed with various acids, including acetic acid, citric acid, hydrochloric acid, and lactic acid, respectively Each catalyst imparts unique properties to the starch, influencing its applications in food, pharmaceuticals, and industrial processes Understanding the effects of these acids on starch can enhance its functionality and performance in diverse formulations.

The evaluation of resistant dextrin production technology revealed that hydrochloric acid catalytic starch resulted in the highest indigestible fraction (IDF) among the tested acids Specifically, hydrochloric acid achieved an IDF of 57.01%, while acetic, citric, and lactic acids showed significantly lower results of 56.45% and 53.34%, respectively.

The indigestible content is 31, comprising 70.82% The three weak acids present exhibit low catalytic ability compared to hydrochloric acid, a strong acid that, despite its lower concentration, demonstrates a significantly stronger catalytic effect.

The whiteness of pyrolyzed samples significantly decreased compared to the raw materials, with CT3 treated with hydrochloric acid showing only 64.27% whiteness, while CT1 with acetic acid had 76.47%, CT2 with citric acid 78.00%, and CT4 with lactic acid 78.87% Acetic, citric, and lactic acid treatments produced dextrin with approximately 80% whiteness Although hydrochloric acid treatment resulted in lower whiteness, it remained within the acceptable range recommended by McClain, ensuring decolorization ability while achieving a high content of indigestible fraction (McClain & Davenport, 2014).

Figure 4.2 Change in whiteness of dextrin pyrolyzed with acetic, citric, hydrochloric or lactic acid as catalyst for 120 minutes

Dextrin with acetic acid catalyst Dextrin with citric acid catalyst

Dextrin with hydrochloric acid catalyst Dextrin with lactic acid catalyst

The solubility of dextrin varied significantly across different formulas, with hydrochloric acid catalyst yielding the highest solubility of 96.73% at 70ºC In contrast, the other three acids exhibited lower solubility under identical conditions This discrepancy is attributed to the incomplete dextrinization of starch, resulting in some insoluble product remaining in its original starch form.

Three formulas of acetic, citric and lactic acids were further pyrolysis at 170°C for up to 300 minutes, the results are shown in Figure 4.3

Figure 4.3 Effect of acetic, citric or lactic acids as catalyst in pyrolysis to produce resistance dextrin at

CT5, CT6, CT7, and CT3 are various types of starches catalyzed by different acids and time durations CT5 is starch treated with acetic acid, while CT6 utilizes clear citric acid for its catalysis CT7 features lactic acid as the catalyst, applied for 300 minutes, and CT3 involves hydrochloric acid for a shorter catalysis period of 120 minutes.

Even after heating starch at 170°C for 300 minutes with acetic, citric, or lactic acids, the whiteness remains negligible However, starch pyrolyzed with these three acids for 300 minutes achieves a whiteness level exceeding 70%, surpassing that of hydrochloric acid at 64.27% The indigestible fraction of the pyrolyzed products treated with the three acid catalysts shows only a slight increase after 300 minutes compared to 120 minutes, remaining below 70%.

The solubility of starch treated with three different acids at 70°C exceeded 80%, yet remained significantly lower than that of hydrochloric acid, which achieved a solubility of 70.82% The production of resistant dextrin using these acids is notably more expensive compared to hydrochloric acid, which is commonly utilized in both research and production For instance, Bai et al (2014) employed hydrochloric acid as a catalyst, mixing it with tapioca starch at a concentration of 0.5M to achieve a pH of 3, with a starch to acid ratio of 1g to 1.5ml Similarly, Kapusniak et al (2017) utilized hydrochloric acid for the pyrolysis of corn starch, maintaining a ratio of 80g of starch to 1.25ml of HCl to produce indigestible dextrin.

4.1.2 Effect of concentration of HCl as catalyst on products of pyrolysis

In this experiment, rice starch M2 was combined with hydrochloric acid (HCl) to achieve specific pH levels of 2.1, 2.3, 2.5, and 2.7 The pH values were determined by mixing 25 grams of starch with 50 milliliters of deionized water in a 1:2 ratio Pyrolysis was conducted at a temperature of 170°C until the whiteness of the samples reduced to approximately 60-63% The findings regarding pyrolysis duration, indigestible fraction (IDF), and the whiteness of the resulting dextrin products are detailed in Table 4-1.

Table 4.1 illustrates that, at a consistent temperature of 170°C, the pyrolysis time required to achieve a whiteness level of 62.4-64% varied significantly among starch samples with different pH levels, influenced by varying HCl addition ratios Specifically, the pyrolysis times for samples M2/2, M2/3, and M2/4 were 28, 65, and 115 minutes, corresponding to pH levels of 2.3, 2.5, and 2.7, respectively Despite the similar whiteness percentages, the indigestible fraction (IDF) content differed markedly, with starch at pH 2.5 yielding the highest IDF value of 72.23%, while pH 2.3 and pH 2.7 produced IDF values of 69.40% and 68.34%, respectively, indicating statistical significance at α 0.05.

The IDF of the dextrin sample at pH 2.7 was limited to less than 70% due to an insufficient amount of catalyzed hydrochloric acid, resulting in a pyrolysis duration of approximately 2 hours This finding aligns closely with previous research that utilized a 1% HCl solution added to starch.

10% (v/w) The main variation in results was due to no pH adjustment but only attention to the amount of HCl, whereas each starch has a different initial pH

Table 4.1 Effect of acid concentration on quality of resistant dextrin products

Figure 4.4 Effect of pH due to acid addition as catalyst on color of resistant dextrin product

The reduction in the indigestible fraction of starch samples at a pH of 2.3 may be attributed to the insufficient reaction time of 28 minutes, coupled with high temperature and acid catalyst, which accelerated color formation and decreased whiteness to 63 During this brief period, the transglucosylation reactions were not fully realized, commencing only when the starch's water content was low This led to the breakdown of starch chains at the (1→4) bonds, allowing them to interact with hydroxyl groups from other chains, resulting in branching points Theoretically, this rearrangement could generate glucosidic bonds (1→2), (1→3), (1→4), and (1→6), which may exist as either α or β-anomers This finding aligns with McClain's assertion that a pH range of 2.2–2.5 is optimal for producing resistant dextrin from starch (McClain, 2010).

4.1.3 Effect of pyrolysis temperature on products of reaction

In this study, two starch namely M1 and M2 were processed at different temperatures of 140, 150, 160, 170, and 180°C Treatment time was 120 minutes with acid clohydric 1% Results are expressed in Figure 4.5, 4.6, and 4.7

The study reveals that increased temperatures significantly decrease the whiteness of starch, with higher temperatures correlating to lower whiteness levels For instance, the M1 starch sample showed whiteness percentages of 87.47%, 75.47%, 66.37%, 52.87%, and 44.17% at temperatures of 140°C, 150°C, 160°C, 170°C, and 180°C, respectively Similarly, the M2 starch sample exhibited whiteness values of 91.07%, 82.80%, 75.03%, 63.97%, and 56.37% under the same temperature conditions This discoloration is primarily attributed to the Maillard reaction, indicating that pyrolysis treatment at 170°C is optimal for both M1 and M2 starch samples.

Figure 4.5 Effect of pyrolysis temperature on quality of resistant dextrin from rice starch M1

( M1/NĐ1: Starch M1 , 140°C, M1/NĐ2: Starch M1 , 150°C, M1 / NĐ3: Starch M1 , 160°C,

M1/NĐ4: Starch M1 , 170°C, M1/NĐ5: Starch M1, 180ºC )

The study revealed that the indigestible fraction of the product varied significantly with temperature At temperatures of 140, 150, 160, 170, and 180°C, the indigestible fraction for M1 was measured at 51.77%, 58.55%, 64.12%, 70.47%, and 74.04%, respectively In contrast, M2 exhibited indigestible fractions of 41.63% and 52.00% at corresponding temperatures.

M1/NĐ1 M1/NĐ2 M1/NĐ3 M1/NĐ4 M1/NĐ5

; 61.35; 68.52 and 71.69% When the temperature increase, the indigestible fraction of

M1 and M2 increases At 170°C and 180°C, M1 and M2 produce dextrin with the highest digestibility (over 68%)

Figure 4.6 Effect of pyrolysis temperature on quality of resistant dextrin from rice starch M2

(M2/NĐ1: Starch M2, 140°C, M2/NĐ2: Starch M2, 150°C, M2/NĐ3: Starch M2, 160°C,

Effects of gamma-ray radiation on rice starch

4.2.1 Effect of gamma-ray radiation on the indigestible fraction

This study examined the effects of varying irradiation doses (5, 10, 20, 30, 40, and 50 kGy) on IR50404 starch to assess the levels of indigestible starch compared to non-irradiated samples The findings, illustrated in Figure 4.11, detail the percentage of indigestible fraction content.

Figure 4.11 Change in indigestible fraction of starch M1 at different irradiation dose

The results indicate that the indigestible fraction of rice starch IR50404 increases with higher irradiation doses, starting from a baseline of 23.39% at 0 kGy Specifically, at a dose of 10 kGy, the indigestible content rises to 27.86%, reflecting an increase of nearly 20% At 30 kGy, the indigestible fraction reaches 30.02%, showing an increase of nearly 30% Furthermore, the increases compared to the control (0 kGy) for the 10, 30, and 50 kGy doses are 19.11%, 28.35%, and 42.28%, respectively.

Vietnamese rice starch IR50404 exhibits a high indigestible fraction, which significantly increases when exposed to gamma radiation doses ranging from 5 to 50 kGy This increase in indigestible content shows a nearly linear relationship with the irradiation dose, as indicated by a correlation coefficient of R² = 0.975.

30 is the maximum allowable food irradiation in Vietnam (10 kGy) and USA (30 kGy), the increase in indigestible fraction is very high (reaching 19.11 and 28.35% respectively).

High-dose gamma irradiation significantly increases the indigestible fraction, particularly at doses of 5-10 kGy, which is noteworthy for its practical implications Unlike moisture-thermal or chemical treatments, irradiation requires a much shorter processing time Although the high levels of indigestible components make the product challenging for food processing, it holds promise for non-food applications These findings are reliable, as they align with similar studies on starch irradiation, including research on rice starch (Yoon et al., 2010; Chung & Liu, 2010; Lee).

& et al, 2013; Shu et al, 2013).

Figure 4.12 Change in indigestible fraction of starch M1 at different irradiation dose

Irradiation dose, kGy 5% moisture content 12 % moisture content

4.2.2 Effect of radiation dose rate on the indigestible fraction

Irradiation of starch at 10 kGy with dose rates of 1, 2, and 3 kGy/h demonstrated significant changes in indigestible content The control sample of natural rice starch showed an indigestible fraction (IDF) of 25.92%, while irradiation increased IDF to 33.46%, 30.28%, and 29.74% for dose rates of 1, 2, and 3 kGy/h, respectively Notably, the 1 kGy/h dose rate resulted in a significantly higher IDF (p < 0.01) compared to the 2 and 3 kGy/h rates, showing an increase of 29.08% over the non-irradiated sample The differences in IDF between the 2 and 3 kGy/h dose rates were not statistically significant.

Figure 4.13 Change in indigestible fraction of irradiated rice starch M1 at different irradiation dose rates

The study demonstrated that the dose rate of irradiation significantly influences the increase of the indigestible fraction in starch When comparing different irradiation dose rates at the same total dose, the indigestible fraction consistently exceeded that of the control (non-irradiated) sample Notably, at a dose rate of 1 kGy/h, the indigestible fraction rose to 33.46%, which is 29.08% higher than the non-irradiated starch sample (Gani et al., 2014).

4.2.3 Effects of gamma-ray radiation on physicochemical properties

4.2.3.1 Effect of irradiation on amylose content

The amylose content of non-irradiated rice starch IR50404 was measured at 16.43%, classifying it as medium high in amylose content Upon irradiation with doses of 5, 10, 20, 30, 40, and 50 kGy, the amylose levels decreased to 14.82%, 14.75%, 14.12%, 12.84%, 12.39%, and 11.08%, respectively Notably, there was a significant reduction in amylose content of 10.23%, 21.85%, and 32.57% at doses of 10, 30, and 50 kGy The highest dose of 50 kGy resulted in a reduction from 16.43% to 11.08% The relationship between amylose reduction and irradiation dose followed a linear trend with an R² value of 0.9653.

Figure 4.14 Change in amylose content of rice starch M1 at different irradiation dose

The observed reduction in amylose content correlates with an increase in antiseptic substances, highlighting a consistent principle and mechanism Additionally, the rise in amylose content with higher irradiation doses (5-50 kGy) aligns with an increase in the indigestible fraction, as indicated by the regression equation y = -0.815x + 17.036, with a strong correlation coefficient of R² = 0.9653.

44 mentioned in section 4.2.1 The results of this study are consistent with a few other studies, where they also indicated irradiation-induced amylose decrease (Lee et al., 2015; Gul et al., 2016)

4.2.3.2 Effect of irradiation on color of rice starch

Figure 4.15 Change in  E of starch M1 at different irradiation dose

The color results are shown in Figure 4.15 The difference in color ΔE of 5 kGy irradiated starch is only 0.24, of 50 kGy irradiated starch is 0.94 The ΔE of doses 10,

The study observed that as the irradiation dose increased from 5 to 50 kGy, the ΔE values rose linearly, with a strong correlation (R² = 0.9697) Specifically, the ΔE values recorded at doses of 20, 30, and 40 kGy were 0.44, 0.50, 0.62, and 0.88, respectively Despite the statistically significant increase in ΔE, the absolute values remained relatively low, all below 1.

High-dose irradiation is known to diminish whiteness and cause yellowing in both food and non-food items This phenomenon operates through mechanisms akin to the thermic effect, which includes the formation of color centers, Maillard reaction products, and caramelization Research indicates that as the dose of irradiation increases, the ΔE value of rice starch also rises, correlating with an increase in the indigestible fraction of irradiated starch The relationship can be expressed mathematically as y = 0.1383x + 0.1027, with a strong correlation coefficient of R² = 0.918.

Irradiation dose, kGy average of delta E with 5% moisture

45 the mechanism is unclear, there is a relationship between an increase in ΔE and an increase in indigestible fraction.

In starch testing, white powder or starch is primarily assessed using a whiteness tester, with Kett's equipment from Japan being the most commonly used While ΔE measurements are rarely employed, our experiment found no visible color difference between irradiated and non-irradiated starch using the Kett C-300 device However, a change in color was observed when analyzing ΔE, marking a unique instance of detecting color differences in starch due to irradiation These findings align with previous research, including the work of Bao et al (2016).

4.2.3.3 Effect of irradiation on solubility and pH of rice starch

Figure 4-16 illustrates the effects of irradiation on starch solubility Non-irradiated starch (0 kGy) shows no water solubility at 25°C A dose of 10 kGy results in negligible changes in solubility, while significant increases are observed only at doses between 20-50 kGy Despite the noticeable enhancement in solubility due to irradiation, the absolute value remains low, with a maximum solubility of just 0.9% at 50 kGy.

Figure 4.16 Change in solubility of starch M1 at different irradiation dose

Increased irradiation doses lead to higher solubility, likely due to a rise in the indigestible fraction content; however, even at high doses, solubility remains low, suggesting that low molecular weight components have a low degree of polymerization (DP 1-9) These components may form but also engage in reactions that contribute to the indigestible fraction The solubility results align with previous studies (Bai et al., 2014; Lin et al., 2018) In comparison to heat treatment, the impact of irradiation on starch solubility is minimal While raising water temperature may enhance solubility, it complicates the detection of irradiation's contribution due to the significant solubility caused by heat.

The pH values of starch samples irradiated at various doses (0 kg, 10, 20, 30, 40, and 50 kGy) were measured, revealing that the control sample (non-irradiated) had a pH of 3.89, while the starch irradiated at 50 kGy exhibited a pH of 3.36 This difference in pH is statistically significant (p < 0.01) Notably, at irradiation doses of 10 kGy and 30 kGy, the pH values decreased significantly by 6.7% and 12.1%, respectively, compared to the non-irradiated reference starch.

Figure 4.17 Change in pH of starch M1 at different irradiation dose

The pH measurement method utilizing a starch solution, composed of 1 part starch to 2 parts water (w/w), effectively identifies pH variations in irradiated samples This method aligns with the standards set by TCVN 10546:2004 for accurate pH assessment.

The gamma-ray radiation as catalysits for pyrolysis to create indigestible dextrin

4.3.1 Change in the indigestible fraction

The study investigated the production of indigestible dextrin from starch subjected to irradiation at doses of 1, 2, and 3 kGy Pyrolysis was conducted at 170ºC for 300 minutes without catalysts Results indicated that, despite the absence of catalysts, the indigestible dextrin (IDF) content in the samples increased significantly, reaching 36.43%, 45.57%, 43.64%, and 42.93% for the respective dose rates.

Irradiation at a dose rate of 1 kGy/h significantly increases the insoluble dietary fiber (IDF) by 25.09% compared to non-irradiated samples (p < 0.01), while showing only modest increases of 4.4% and 5.15% compared to dose rates of 2 and 3 kGy/h, respectively Additionally, the effect of dose on post-pyrolysis IDF increase is more than halved compared to pre-pyrolysis levels, with no significant differences observed among the higher dose rates.

54 in IDF between dose rates 2 and 3 kGy/h Thus, low dose rates (1 kGy/h) have IDF higher than high dose rates

Figure 4.24 Changes in indigestible fraction of pyrodextrin from irradiated rice starch M1 at different dose rates, without acid catalysis at (170  C, 300mins)

At a dose rate of 1 kGy/h, starch reaches the highest indigestible fraction content after pyrolysis, while higher dose rates yield lower results, highlighting the efficiency of this dose for large-scale production and cost reduction in irradiation These findings align with the research conducted by Chung and Liu (2009).

4.3.2 Change in the whiteness of dextrin

The study analyzed the whiteness change of dextrin derived from irradiated rice starch at varying dose rates, revealing that after pyrolysis with an acid catalyst at 170°C for 300 minutes, non-irradiated starch maintained a high whiteness level of 72.5% In contrast, irradiated starch samples exhibited reduced whiteness, with the 10 kGy dose leading to significant discoloration The whiteness of pyrodextrin from irradiated starch at doses of 1, 2, and 3 kGy/h was measured at 66.5%, 69.2%, and 68.4%, respectively, with the 1 kGy/h dose causing a significant decrease in whiteness (p < 0.01) compared to the higher doses.

55 difference in absolute value is not too large to consider when choosing irradiation practice

The study reveals that varying the irradiation dose rates does not significantly affect the color of starch at the same irradiated dose, with all samples maintaining approximately 70% whiteness, similar to non-irradiated samples.

Figure 4.25 Change in whiteness of pyrodextrin from rice starch M1 irradiated at different dose rates, without acid catalyzed

4.3.3 Change in the solubility and pH of dextrin

The solubility of rice starch pyrodextrin was significantly affected by irradiation, as shown in Figure 4-26 Natural starch pyrolysis at 170ºC for 300 minutes resulted in a solubility of only 92.8%, with conventional heating at 70ºC leading to cloudiness due to gelatinization In contrast, irradiated samples exhibited nearly complete dissolution under the same conditions, with no notable differences in solubility across varying dose rates Specifically, the solubility for the dose rates of 1, 2, and 3 kGy/h was recorded at 98.2%, 97.5%, and 98.3%, respectively.

Irradiation dose rate, kGy/h whiteness

The results indicate that higher irradiation rates lead to increased starch solubility, attributed to enhanced polarity from chain fracture and reduced hydrogen bonding between chains (Liu et al., 2012) This finding aligns with the research of Atrous et al (2015), which observed similar effects across various starch types when irradiation dose rates were elevated.

Figure 4.26 Change in the solubility of pyrodextrin from irradiated rice starch M1 at different irradiation dose rates, not acid catalytic

4.3.4.1 Results of X-ray diffraction of starch irradiated as catalyst for pyrolysis

Figure 4.27 Results of XRD diffraction of starch M1 at different irradiation doses for pyrolysis

Irradiation dose rate, kGy/h solubility

XRD diffraction analysis indicates that heat-treated samples exhibit minimal structural changes when subjected to irradiation under varying conditions, yet they differ significantly from natural starch samples Notably, the intensity of certain peaks diminishes in heat-treated and irradiated samples compared to natural starch, with the peak at 2θ = 11.4° completely absent in the spectra of irradiated and pyrolysis starch Additionally, peak intensities at angles 2θ = 15.3°, 17.4°, 18.3°, and 23.1° are reduced in both irradiated and pyrolysis starch relative to natural starch, while a broad peak with low intensity between 19.7° and 20.7° shows a significant decrease in the irradiated and pyrolysis samples.

4.3.4.2 FTIR results of starch irradiated as catalyst for pyrolysis

Figure 4.28 FTIR of starch M1 at different irradiation doses with pyrolysis

The FTIR spectrum reveals key covalent fluctuations, including the apex -OH group oscillating in the wide frequency range of 3000-3600 cm -1, and the deformation of the -OH group at 1,339 cm -1 Additionally, the -C-OH group exhibits covalent oscillation between 1076-1148 cm -1, while the -CH group oscillates within 2800-2950 cm -1, with variation deformation occurring in the -CH- group from 860-994 cm -1 Notably, FTIR spectra under various irradiation conditions indicate no changes in the functional groups or structural bonds of starch.

4.3.4.3 TG results of starch at different irradiation doses without catalyst

Figure 4.29 TG results of starch M1 at different irradiation doses with pyrolysis

The analysis reveals that natural starch samples exhibit greater weight loss compared to irradiated starch samples when subjected to varying irradiation doses and pyrolysis Specifically, starch treated with a 10 kGy irradiation dose demonstrates the lowest weight loss, followed closely by samples with a 30 kGy irradiation dose and natural starch undergoing pyrolysis However, the differences observed may be minimal and could be influenced by the varying humidity levels of the different samples.

4.3.4.4 SEM results of starch at different irradiation doses with pyrolysis

Figure 4.30 SEM pictures of starch M1 at different irradiation doses with pyrolysis

Surface SEM showed no surface modification of starch due to irradiation

4.3.4.5 DSC results of starch at different irradiation doses with acid catalyst for pyrodextrin

Figure 4.31 DSC results of starch M1 at different irradiation doses with acid catalyst for pyrolysis

The effect of gamma-ray radiation combined with acid catalyst on pyrolysis to

to create resistance dextrin from rice starch

4.4.1 Pyrolysis having the same duration

In this experiment, rice starch IR50404 5% moisture content irradiated 5, 10, 20,

30, 40 and 50 kGy 0 kGy was considered as a non-irradiated control Then pyrolysis at 170°C for 350 minutes Fast cooling and analyze the content of indigestible and some other criteria.

The results presented in Figure 4.32 indicate a significant increase in the indigestible fraction of control starch due to pyrolysis, rising from approximately 25% to 36.1% Additionally, the indigestible fractions of fecal products from samples irradiated with doses of 5, 10, 20, 30, 40, and 50 showed values of 38.5%, 42.49%, 41.93%, 45.37%, 45.46%, and 44.2%, respectively.

Irradiation at 50 kGy resulted in a significant increase in the indigestible content of products, with percentage increases of 7.34%, 17.4%, 16.15%, 25.68%, 25.92%, and 22.43% observed in samples treated at 5, 10, 20, 30, 40, and 50 kGy, respectively, compared to the control The relationship between the indigestible fraction and the percentage increase in indigestible fraction as a function of irradiation dose follows a logarithmic pattern within the 5-50 kGy range, represented by the equation y = -0.9832x² + 11.88x - 11.4.

Irradiation acts as a catalyst akin to acid addition, enhancing the pyrolysis process to effectively break down the indigestible fraction Research indicates that irradiation reduces starch pH (Liu et al., 2012), which may contribute to its effectiveness Additionally, irradiation alters structural properties that improve thermal responses during pyrolysis However, the lengthy pyrolysis time of 350 minutes poses challenges for industrial scalability.

The results indicate that higher irradiation doses lead to an increase in the indigestible starch content after pyrolysis, aligning with the findings presented in section 4.2, where an increase in irradiation dose from 0 resulted in similar trends.

Irradiation at 30 kGy significantly enhances the digestive resistance of starch, surpassing levels observed at both 40 and 50 kGy, as demonstrated in studies by Reddy et al (2015) and Polesi et al (2016) Additionally, while the indigestible content of starch tends to increase at 50 kGy, the effects of irradiation on pyrolysis have also been investigated.

Figure 4.32 Indigestible fraction of pyrolysis starch M1 (170  C, 350 minutes) with catalytic irradiation

Determining the optimal time to stop pyrolysis is challenging due to variable factors like raw materials, pH, and temperature In this experiment, instead of relying on time, the whiteness of the dextrin product post-pyrolysis was utilized as the key indicator, with all samples timed to achieve a target of 65% whiteness The relationship between whiteness and time is expressed by the equation y = 13.514ln(x) + 0.0038, with a correlation coefficient of R² = 0.9078.

% in cr e ase o f i n d ig e sti b le in d ig e sti b le fr ac tion ,% irradiaton dose, kGy indigestible fraction % increase of indigestible

The results of the indigestible fraction indicate that samples achieve 65% whiteness within 50-60 minutes, with control starch reaching this level in 60 minutes and 50 kGy irradiated starch in just 50 minutes Although both types of starch exhibit similar whiteness levels, the indigestible fraction (IDF) increases with higher radiation doses Non-irradiated starch has an IDF of 65.03%, which rises to 68.86%, 69.55%, and 71.09% for irradiation doses of 10 kGy, 30 kGy, and 50 kGy, respectively The percentage increases in IDF compared to non-irradiated starch are 5.89%, 6.95%, and 9.32% for the 10 kGy, 30 kGy, and 50 kGy doses, respectively.

Irradiation combined with hydrochloric acid pyrolysis (0.5%, 170ºC) significantly enhances the indigestible fraction This effect is observed at specific intervals during pyrolysis, particularly at 60 and 80 minutes, as well as at the conclusion of the process, achieving a consistent whiteness of 65%.

The findings align with the results from section 4.2, indicating that elevated temperatures stimulate an increase in indigestible content within the mat Additionally, extending the pyrolysis time further raises the indigestible content; however, product coloration becomes a concern, necessitating a limit of 60 minutes for the process.

Figure 4.33 Effect of irradiation and pyrolysis on indigestible fraction of pyrodextrin at the same time

4.4.3 Pyrolysis at different temperatures to the same 65% whiteness

A study investigating HCl catalytic pyrolysis at temperatures of 150, 160, and 170°C with a mixing ratio of 0.75% revealed consistent product whiteness of 65%, as illustrated in Figure 4-34 The findings indicate that irradiation effectively preserves a high level of indigestible fraction, with increased doses (ranging from 10 to 50 kGy) enhancing this effect.

In comparing pyrolysis temperatures, it was found that both 160°C and 170°C yield an IDF higher than that at 150°C, with no significant difference between 160°C and 170°C Therefore, when incorporating HCl as a catalyst at a rate of 0.75% or more in the pyrolysis of irradiated starch, it is advisable to use a temperature of 160°C instead of 170°C, particularly with an HCl/starch ratio of 0.05% Utilizing higher temperatures is not only energy-inefficient but also reduces pyrolysis time excessively, complicating the control of product quality.

The findings indicate that a temperature of 160°C yields the highest content of indigestible fraction, aligning with the observation that increasing irradiation doses also enhance indigestible content This suggests that 150°C may not provide sufficient heat for complete reactions Therefore, the pyrolysis of starch, when irradiated with a catalyst at 160°C, produces optimal results.

Figure 4.34 Effect of irradiation and pyrolysis on indigestible fraction of pyrodextrin with the same 65% whiteness at different temperatures

4.4.4.1 Results of X-ray diffraction of starch irradiated combined acid catalyst for pyrolysis

Figure 4.35 Results of XRD diffraction of starch M1 at different irradiation dose combined acid

XRD results indicate that the presence of HCl significantly lowers peak intensity compared to its absence During pyrolysis, the orderly arrangement of amylose's linear portions is disrupted, leading to the breakdown of amylopectin branching points This process results in the degradation of the ordered phase and an elongation of the amorphous phase, reflecting a deterioration of the crystal phase and an increase in the amorphous phase.

4.4.4.2 FTIR results of starch irradiated combined acid catalyst for pyrolysis

Figure 4.36 FTIR of starch at different irradiation doses with acid catalyst for pyrolysis

The FTIR spectrum reveals several key features: the covalent fluctuation of the apex -OH group occurs within a wide frequency range of 3000-3600 cm -1, while the oscillation deformation of the -OH group is noted at 1,339 cm -1 Additionally, the covalent oscillation of the -C-OH group is observed between 1076-1148 cm -1, and the -CH group oscillates within the frequency range of 2800-2950 cm -1 The variation deformation of the -CH- group is found between 860-994 cm -1 Importantly, FTIR spectra under different irradiation conditions indicate that there are no changes in the functional groups or structural bonds of starch.

4.4.4.3 TG results of starch at different irradiation doses with acid catalyst for pyrolysis

Figure 4.37 TG results of starch M1 at different irradiation doses with acid catalyst for pyrolysis

The analysis reveals that rice starch experiences weight loss at varying irradiation doses when subjected to acid catalyst and pyrolysis Notably, natural starch samples exhibit a higher weight loss compared to irradiated starch samples treated with acid catalyst and pyrolysis, although the difference is minimal, potentially influenced by the moisture content in the samples.

4.4.4.4 SEM results of starch at different irradiation doses with pyrolysis

CX10-HCl-PN CX30-HCl-PN

Figure 4.38 SEM pictures of starch at different irradiation doses with acid catalyst for pyrolysis

4.5 The effects of gamma-ray radiation, acid and activated carbon on pyrolysis create pyrodextrin from rice starch

4.5.1 The effect of activated carbon with different rate added

Technological flowchart and its verification at pilot scale

4.6.1 Process flowchart and process description

Process diagram is shown in Figure 4.47

Step 1: Raw rice or rice starch

High-quality white rice, specifically varieties such as IR50404 or OM576, should contain a high amylose content greater than 25% It must be thoroughly milled to achieve a pure white appearance, free from bran and impurities Additionally, the rice should maintain its quality without any loss during preservation, with a humidity level not exceeding 12%.

Rice starch is produced from wet milled rice, broken rice, or ground dry rice, and is refined to meet stringent purity standards The preparation process ensures that the starch contains less than 1% protein and less than 0.3% lipid, while also keeping impurities, heavy metals, and microorganisms below permissible levels Additionally, the starch particles must pass through a sieve with sizes of 125/90, ensuring high-quality starch suitable for various applications.

Step 3: Drying reduces the moisture

Starch with moisture content exceeding 12% must be dried to achieve a level of 4-5% for optimal suitability in the subsequent irradiation process If the moisture is between 5% and 12%, drying may not be immediately necessary, but it can be performed after irradiation to reach the desired moisture level Once drying is completed, the starch should be allowed to cool before sealing in a bag for irradiation as outlined in step 4.

Package for irradiation: For irradiation at the Hanoi Irradiation Center, it is necessary to prepare 4 boxes with internal dimensions of 50 cm x 40 cm x 30 cm (L x

Barrels should be constructed from thin boards to prevent breakage, puncturing, or deformation during irradiation, rotation, and transportation to and from the irradiation chamber Additionally, it is essential that containers are tightly sealed to maintain their integrity.

The tank features a tight cap to prevent dough from escaping and has flat top and bottom surfaces for secure stacking It can hold starch in quantities ranging from 580 to 650 kg/m³, ensuring it is completely filled when closed.

Figure 4.46 Illustration of the location of the starch tanks in the irradiation chamber

The boxes are arranged symmetrically on each side of the source board, with two tightly stacked boxes per side The sample box holder is positioned 100 cm above the base of the irradiation chamber, while the center box is located at the center of the source board Additionally, there is a distance of 63 cm from the hole to the plane of the adjacent sample container Proper positioning of the starch containers for irradiation is illustrated in Figure 4-46.

Irradiation doses for starch used in food processing can reach a maximum of 10 kGy at a dose rate of 1-2 kGy/h, while for non-food applications, doses can go up to 30 kGy with a dose rate of 3-5 kGy/h.

Step 5: Mix the acid catalyst solution

Using hydrochloric acid as the catalyst for the pyrolysis reaction Acids of ≥ 36.5% purity and must be of food grade Dilute acid with a solution of 1.5% in

To achieve a starch pH of 2.4, spray 74 deionized water onto dry starch with a moisture content of 4-5% Use an acid spraying nozzle equipped with a pressurizer, and ensure that the spraying process is combined with high-speed stirring for an adequate duration to guarantee even mixing of the acid into the powder.

Step 6: Incubate with acid catalyst

To ensure proper incubation, starch combined with an acid solution should be stored in closed containers for a duration of 5 to 12 hours, preferably overnight During this incubation period, it is essential to mix the solution at a very low speed of 10 rolls per minute.

Step 7: Drying reduces the moisture

It is necessary to reduce moisture of acidified starch by drying similar to step 3 introduced The equipment in step 8 can be used together for drying Drying mode at

To achieve optimal drying, it is essential to maintain a temperature of 105°C until the humidity drops to 4-6% Humidity levels can be assessed using a rapid measuring device or through experience with specific machinery Drying materials with a moisture content below 3% is unnecessary, as it wastes time and energy and can lead to the creation of locally burnt particles during the roasting process.

After drying to reduce moisture, increase the temperature for roasting at 160°C for 80 to 90 minutes until the flour's whiteness drops to 60–65% Use a Kett - C300 powder whiteness meter or a similar device to measure starch whiteness It is advisable to create roasted starch samples with standard whiteness levels of 60% or 65% for color comparison during roasting Avoid roasting to a whiteness level below 60% to ensure easier color removal when producing maltodextrin later.

To maintain the quality and color of dried products, it is essential to cool them quickly to below 70ºC, as leaving them in a pile while still hot can negatively impact their properties This can be achieved by spreading the products on a large tray, using a spacious tank, or employing a specialized cooling device with a chiller layer.

Figure 4.47 Schematic diagram of the production process of indigestible rich pyrodextrin from irradiated rice starch

Step 10: Pyrodextrin intake and quality control

After drying, the product must be sifted to eliminate lumps and impurities, followed by crushing and a second sifting The packaging serves as raw material for further processing and can be stored either separately or sealed It is essential that the packaging is quantitative.

Product quality should be checked for each batch based on whiteness, solubility and especially indigestible fraction rice

Mix the acid catalyst solution

Pyrodextrin intake and quality control

4.6.2 Quality parameters of final product

Table 4.4 The quality of final product

Figure 4.48 Weight reduction of starch samples during different processing conditions

Non-irradiated starch samples exhibited a greater mass reduction compared to irradiated samples, although the difference was minimal, likely influenced by the moisture content of the various samples.

The heat treated starch samples combined with irradiation had a greater mass reduction than irradiation combined with heat treatment and HCl and much higher than irradiation alone

Table 4.5 The weight reduction of specific samples

Irradiation combined acid catalyst and pyrolysis

CONCLUSION AND RECOMMENDATION