1 HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION FACULTY FOR HIGH QUALITY TRAINING GRADUATION PROJECT Thesis code [2022-18116002] INFLUENCES OF FORMULATIONS, PROCESSING CONDI
Introduction
Research rationale
Germinated brown rice offers significant health benefits due to its higher nutritional value compared to regular brown rice, particularly in vitamins, antioxidants, and gamma-amino butyric acid (GABA) GABA, an amino acid that functions as a neurotransmitter, has been shown to provide calming effects and support brain development in children, as well as aid in healing overactive children and those with autism Increasingly, products made from germinated brown rice, such as germinated brown rice milk, are being developed for easier consumption However, the processing and preservation of GABA can lead to its loss, primarily due to heat exposure, which research indicates significantly reduces GABA levels Additionally, factors such as the rice-water ratio and extraction time can influence the GABA content and overall nutrient retention GABA also interacts chemically with other components in rice, with these interactions often driven by catalysts like enzymes or lipid oxidation.
To retain the GABA content in germinated brown rice milk, it is essential to determine optimal processing conditions, suitable formulations, and preservation methods This study investigates the effects of various parameters, including soaking time, rice-to-water ratio, preservation temperature, and different thickening agents such as xanthan gum, guar gum, and pectin.
Objective of the thesis
The main objective of this thesis is to investigate the influences of different processing factors for determining the most suitable parameters for manufacturing germinated brown rice milk
- Achieve the suitable temperature and time for thermalizing the germinated brown rice milk with minimal loss of GABA
- Determine the suitable soaking time and ratio parameters for achieving the suitable GABA post soaking
- Determine the preserving method and food safety parameters of the GBRM
- Determine the suitable formulation of food additives (xanthan gum, guar gum, pectin) and their effects on the GABA content and quality of the germinated brown rice milk
- Evaluate the sensory criteria of the germinated brown rice milk
Meaning of the thesis
This thesis results an be used as a reference for developing the production procedures of germinated brown rice milk and further studies on the processing of related food products i
Literature review
Overview about germinated brown rice
Rice (Oryza sativa L) is a vital cereal and a primary staple food globally Recent trends have focused on enhancing its nutritional value through germination, particularly increasing Gamma-aminobutyric acid (GABA) levels Germinated brown rice (GRB), which is unpolished rice that has undergone germination, offers improved texture and flavor, along with a significant boost in GABA content This nutritious variant is popular in various cuisines, including Japanese and Korean, and is recognized for its superior nutritional profile compared to regular white rice.
The nutritional value of brown rice is compared with milled white rice and rice bran is described in the Table 2.1
Table 2 1:Comparison of nutritional values of brown rice, milled and rice bran[8]
Germinated brown rice is produced by soaking ungerminated brown rice in warm water at temperatures between 30-40 degrees Celsius, which activates enzymes like phytase, lipase, α-amylase, and β-amylase essential for germination This process enhances the nutritional profile of the rice, resulting in a product rich in Gamma-aminobutyric acid (GABA), inositol, fibers, vitamins, magnesium, and various antioxidants.
Overview about germinated brown rice milk
2.2.1 Introduction about germinated brown rice milk
Rice milk is a plant-based, non-dairy beverage that serves as an excellent alternative for individuals with lactose intolerance This cereal product, part of the bran milk category, is made by soaking milled rice in water, creating a slurry that is then filtered to eliminate large particles To enhance its texture, rice milk is treated with amylase enzymes, which partially break down the starch content, resulting in a smooth suspension Other popular bran milk options include soybean milk and peanut milk, making rice milk a versatile choice in the growing market of non-dairy beverages.
Figure 2 1:Germinated brown rice and germinated brown rice milk
Bran milk products commonly face the issue of precipitate separation during storage due to the emulsion of water and non-uniform milled rice particles, which depend on the milling device's properties Over time, these particles settle at the bottom, compromising the product's stability and sensory qualities To address this problem, incorporating stabilizers like xanthan gum, guar gum, or pectin into the rice milk solution can enhance its stability.
Figure 2 2:The structure of Gamma-amino butyric acid
Gamma-aminobutyric acid (GABA) is a beneficial compound found in germinated rice and various plants As an inhibitory neurotransmitter, GABA promotes better sleep and a calmer mood Research indicates that GABA supplementation can effectively reduce stress and anxiety It is regarded as a vital nutrient in germinated brown rice (GBR), contributing positively to the nervous system through its synthesis during the germination process.
During rice bran germination, the enzyme glutamate decarboxylase (GAD) catalyzes the irreversible conversion of l-glutamic acid (Glu) into gamma-aminobutyric acid (GABA) and carbon dioxide.
Figure 2 3:Synthesis pathway of GABA in rice
Various methods have been developed to enhance the GABA content in germinated brown rice (GBR), primarily by optimizing the germination process Key factors include controlling time and temperature, implementing biological modifications, and utilizing gaseous treatments These approaches have demonstrated significant improvements in GABA yield following germination.
Gamma-aminobutyric acid (GABA) is the main inhibitory neurotransmitter in the central nervous system (CNS) and operates through ligand-gated ion channels Antiepileptic drugs (AEDs) primarily enhance GABA's inhibitory transmission Research indicates that GABA also plays a crucial role in the brain development of children For children aged 5 to 10, products containing GABA can promote better development and improve sleep quality In specific cases, GABA rice milk serves as an alternative for hyperactive children.
2.2.3 Factors affect the stability of GABA in a product a Heat
GABA, an amino acid, is significantly affected by heat during processing, with most amino acids tolerating temperatures up to 120°C However, GABA begins to degrade at 121°C, and even lower heat treatments can reduce its content Research indicates that heating products at 80-90°C results in a notable decrease in GABA levels.
GBR is a starch-rich grain that undergoes significant changes during germination, primarily due to the activity of enzymes like α-amylase This process breaks down starch into simple sugars, which then interact with amino acids during heat treatment, leading to non-enzymatic browning known as the Maillard reaction Consequently, a decrease in GABA content can be anticipated.
GABA naturally diminishes during preservation, and various preservation methods that regulate time, temperature, and conditions have been shown to impact the retention of GABA in products.
2.2.4 Nutritional value of germinated brown rice milk a Starch
Starch, the primary component of rice grain and its main nutrient, consists of glucose monomers linked by 1,4 glycosidic bonds It has two structural forms: amylose, which is linear, and amylopectin, which is branched Upon consumption, starch is broken down by the enzyme α-amylase into small linear malto-oligosaccharides, which are further hydrolyzed by α-glucosidases and maltase-glucoamylase, as well as sucrase-isomaltase, into glucose This glucose is then absorbed and transformed into energy for the human body.
Starch serves as the primary nutrient and structural component in rice milk, contributing to its characteristic white turbidity To achieve a uniform texture and enhance the sensory quality of rice milk, it is essential to homogenize the starch particles effectively.
GABA in germinated brown rice (GBRM) is produced during the germination process, offering health benefits such as stress reduction and improved sleep quality Additionally, GBRM is a source of essential vitamins.
Brown rice contain mainly vitamins B1, B3, B6 and other health beneficial vitamins[24] These vitamins mainly play a role in the immune system and cell repair
2.2.5 Health benefits of rice milk
Rice milk and other plant-based milk alternatives serve as effective substitutes for various consumer groups, particularly those who are lactose intolerant Lactose intolerance is a digestive condition where the small intestine fails to absorb lactose, leading to unpleasant symptoms such as vomiting, nausea, and diarrhea upon consuming dairy This reaction is primarily due to the insufficient presence of the lactase enzyme, specifically β-D-Galactosidase Additionally, individuals with milk protein allergies can benefit from rice milk, as traditional animal-based milk contains casein and whey proteins that may trigger allergic reactions.
Rice milk is a versatile beverage that supports various lifestyles and provides essential nutrients for an active daily life Regular consumption of rice milk delivers these nutrients to the body more efficiently than a limited diet.
Rice milk is an excellent option for individuals with busy schedules and for vegetarians who avoid animal-based products As a plant-based beverage primarily composed of starch and essential vitamins, rice milk offers the necessary nutrients and benefits that align with a vegetarian lifestyle.
2.2.6 Overview of thickening agents used in processing of GBRM
Researches about GBRM in Vietnam
Since the introduction of Germinated Brown Rice (GBR) to Vietnam's food science community, numerous studies have been conducted by researchers focusing on the production capabilities of GBR and Germinated Brown Rice Milk (GBRM) Currently, the Vietnamese market features a variety of germinated brown rice milk products.
2013; T Thị et al., 2017; Tú et al., 2016).
International Researches about GBRM in foreign
Recent studies have concentrated on enhancing the germination process by exploring various factors influencing GABA yield rates Notably, Dhakal et al utilized Lc Lactis subsp lactis PU1 to achieve a significant GABA yield of 1031 ± 9 mg/kg in chickpea sourdoughs.
In 2022, Munarko et al demonstrated that various types of Indonesian germination yield different levels of GABA content after germination Their research indicates that the GABA content is significantly influenced by the germination method and its parameters Therefore, selecting a reputable manufacturer of germinated brown rice milk is essential to achieve the desired GABA content for this study.
In Japan and Korea, rice milk is widely consumed, with brown rice milk emerging as a healthier alternative to traditional rice milk Currently, brown rice milk is gaining popularity in the industry, and research has focused on how heat and pH regulation influences GABA content However, there is a lack of studies exploring the impact of other food additives on GABA levels.
Germinated brown rice milk is a nutritious alternative to traditional plant-based milk, offering essential health benefits and appealing to a wide range of consumers.
GABA is a crucial substance that aids individuals with various psychological health issues It is essential to preserve the GABA content in germinated brown rice milk, as factors such as heat, chemical composition, formulation, and preservation can negatively impact its levels The loss of GABA not only diminishes the product's value but also reduces the intended health benefits of consuming germinated brown rice milk.
Materials and methods
Materials
The GBR used is Vibigaba GBR which is obtained at Gao Mam Vibigaba retailer in District 10,
In Ho Chi Minh City, analytical grade chemicals such as Xanthan gum, Guar gum, Pectin, Acid boric, Phenol, Sodium hypochlorite, and Borax are sourced from the Hoa Chat Bach Khoa chemical store located in District 10 Additionally, enzyme amylase is obtained from Angel Biotic, Inc., a retailer in District 1.
Methods
The process for producing the germinated brown rice is shown in the figure 3.1
Figure 3 1: Diagram of experimental design
Germinated brown rice has a hardened structure that complicates milling; however, soaking it in warm water at 40°C allows the starch to absorb water, resulting in a swollen, softer grain This process exposes the whole grain by expanding the starch matrix, making it easier to mill Additionally, soaking at warm temperatures gelatinizes the grain, enhancing its physical, chemical, viscosity, rheological, and nutritional properties, which are essential for producing rice milk.
In 2015, Kale et al demonstrated that soaking rice at 40°C minimally impacts its chemical composition, while higher temperatures can reduce starch and vitamin content Therefore, using water at 40°C is the most effective method for soaking rice.
Milling rice with the Oku San No Miller Series 1000 involves a wet milling process, which makes the rice swollen and softer compared to unsoaked rice, resulting in a higher milling yield The choice of milling device significantly influences the particle size of the rice, as factors like milling speed and blade sharpness can reduce particle size After the milling process, unprocessed GBR milk is obtained.
After milling, rice milk often contains large, coarse particles that lead to separation and an undesirable texture To achieve a smoother product, the rice milk is filtered through a cloth bag Additionally, enzyme treatment can be applied to enhance the quality of the rice milk.
The rice milk is treated with amylase enzyme to partially breakdown the starch particles for the purpose of increasing the stability of the product e Homogenizing
Stabilizers and thickeners, such as xanthan gum, guar gum, and pectin, are incorporated into the product to enhance its stability These additives are measured and added to the GBRM mixture at varying concentrations of 0.1%, 0.3%, and 0.5% (m/v) The mixture is then thoroughly blended using a homogenizer to ensure even distribution of the stabilizers.
3.2.1.1 Determination of soaking time for preparation
Soaking is a crucial step in the production of GABA-rich brown rice (GBRM), as unprocessed GBR has a hardened structure that hinders optimal milling efficiency Research is conducted to identify the most effective soaking duration in warm water, which directly impacts the GABA extraction rate from the rice, since the primary GABA content is located within the grain.
The soaking time for GBRM production is presented in the following table
Table 3 1:Ratio of rice – water for soaking of GBR
To determine the GABA yield based on soaking time efficiency, the GABA solution should be centrifuged using a centrifugation machine The supernatant is then collected and transferred into a test tube, following the method outlined in reference [49] The measurement is conducted using an equation to calculate the maximum GABA extracted corresponding to their respective soaking times.
3.2.1.2 Determination of water – rice ratio for preparation
The water-to-rice ratio during milling significantly influences the GABA content in GBRM, as water serves as the primary component that retains GABA after the filtration process.
Table 3 2: Ratio of rice to water and time for soaking of GBR
Soaking time (h) 8h 8h 8h Ratio (rice-water) (g/g) 1:5 1:10 1:15
To determine the GABA yield for optimal soaking time efficiency, the GABA solution should be centrifuged using a centrifugation machine The supernatant is then collected and transferred into a test tube, following the method outlined in reference [49] The measurement is conducted using an equation to calculate the maximum GABA extracted based on the rice-to-water ratio.
Rice milk samples are prepared and stored in 100ml Duran sterilization bottles, which are sterilized for 15 minutes using an autoclave After sterilization, the samples are cooled to room temperature and stored at temperatures of 5°C, 10°C, and 25°C.
Rice milk and other bran-based milk products are rich in nutrients, starch, and protein, creating an ideal environment for pathogenic microorganisms that can lead to spoilage Primarily, aerobic bacteria thrive by utilizing starch and sugar through aerobic respiration To identify the best preservation methods for grain-based rice milk (GBRM), it is essential to investigate the optimal temperature and duration for storage by monitoring changes in pH and microbial levels Daily samples are collected and analyzed every 24 hours following the sterilization of the rice milk.
3.2.2.1 Method for determination of GABA content using UV-VIS spectrophotometry
Various methods exist for measuring GABA content in products, including High-Performance Liquid Chromatography (HPLC) and UV-Vis spectrophotometry The UV-Vis spectrophotometry method is specifically employed to assess GABA levels in GBRM, utilizing analytical grade chemicals and a GABA standard solution.
The standard curve is prepared by dissolving 0.1g of GABA in 100ml diluted water (1000 àg/ml)
A series of sample with concentration from 200àg/ml to 1000àg/ml is prepared to build a standard curve The result is expressed in àg/g b Borate buffer preparation
To prepare a borate buffer solution, accurately weigh 2.54g of borax and 4.7g of boric acid Mix these two chemicals and adjust the total volume to 1000ml using a 1000ml volumetric flask.
The phenol 6% solution is prepared by dissolving 6 ml of phenol into 100ml of diluted water d Sodium hypochlorite preparation
Sodium hypochlorite 6% solution is prepared by weighing 6g of NaClO and dissolve it into 100ml of diluted water e The GABA standard curve
To create the GABA standard curve, all chemicals are combined in a test tube according to the formula provided in the table, followed by boiling the mixture for 10 minutes until a blue color develops The resulting solutions are then placed in separate cuvettes and analyzed using a UV-VIS Spectrophotometer at a wavelength of 630 nm The GABA standard curve is illustrated in Appendices 12 and 13, with the trendline and curve formula calculated using Microsoft Excel 2016.
To calculate the GABA content, we use the equation to calculate the GABA contnent:
3.2.2.2 Determination of viscosity of GBRM with the addition of different thickeners
The viscosity of the GBRM was determined using a Brookfield Viscometer with the addition of xanthan gum, guar gum, and pectin at varying concentrations of 0.1% g/ml, 0.3% g/ml, and 0.5% g/ml Measurements were conducted using S61 and S62 measurement cylinders, with results expressed in mPa The viscosity was assessed at three different speeds: 50 rpm, 60 rpm, and 100 rpm.
3.2.2.3 Determination of stability of GBRM i
Statistical analysis
The experiments were conducted in triplicate, and the results are presented as mean values ± standard deviation To assess the differences among the means, statistical analysis was performed using analysis of variance and Duncan's Multiple Range Test (DMRT) at a 95% significance level.
Result and discussion
Determination of the suitable soaking time and ratio of rice for achieving GABA
Figure 4 1: GABA content (àg/ml) by soaking time and ratio of rice to water
The line chart in Figure 4.1 illustrates the GABA content in germinated rice samples soaked for varying durations (0h to 12h) and ratios (1:5, 1:10, 1:15) GABA levels are detectable only after 4 hours of soaking, with the lowest content observed at this duration due to the hard outer layer of germinated brown rice, which hinders the milling process Un-soaked germinated brown rice (0h) is the least effective for consumption The 1:5 ratio yields the highest GABA content, increasing from 125 µg/ml at 4h to 517 µg/ml at 12h, as it has the lowest concentration of water to rice Although the 1:15 ratio is more economical for industrial production, it results in the lowest GABA content due to a higher solution volume The 1:10 ratio shows a GABA trace of 66 µg/ml at 4h and 376 µg/ml at 12h, making it optimal for both scientific research and economic considerations, as it achieves detectable GABA levels at 4h while supporting higher production volumes.
Soaking is the initial step in rice milk production, allowing the rice to absorb moisture, which expands the starch matrix and softens the outer layer for effective wet milling This process requires sufficient time to achieve optimal soaking conditions GABA is primarily extracted during the milling of the kernel, where it is formed.
GABA CONT ENT BY SOAKING T IME AND RAT IO
Soaking rice enhances milling efficiency and increases the retrieval rate of GABA in the production of germinated brown rice (GBRM) Although germinated brown rice is rich in GABA, some of this compound remains in the rice residue after filtration through a cloth bag.
Table 4 1:Proximate composition of germinated brown rice milk product
Nutrient Percentage (%) Method of determination
EVN-R-RD-2-TP-3498 (Ref FAO Food 14/7-1986)
The nutritional analysis of GBRM reveals a total solid content of 12.40% (w/v), with protein at 0.91% (w/v), fiber at 0.8% (w/v), fat at 0.3% (w/v), and ash at 0.39% (w/v) Additionally, the sugar content is 7.00% (w/v), which includes 5% added sugar during mixing and the remainder derived from the hydrolyzation of α-amylase on starch granules These findings align with previous research on the nutritional value and solid content of rice milk.
For optimal GBRM production in research, the recommended process involves soaking rice in a 1:10 ratio of rice to water for 8 hours.
Sensory evaluation of the GBRM
Figure 4 2:Sensory evaluation of GBRM
The sensory evaluation of germinated brown rice milk involved 20 testers, revealing an average color rating of 7.1, characterized as a whitish or cream hue The aroma of the rice milk is pleasant, with no off-putting smells Its flavor is noted to be sweet with a hint of sourness The texture is described as liquid with small starch particles, exhibiting a uniform consistency and no residue.
Overall, the GBRM of this research has the same sensory evaluation results with other rice milk product on the market as well as researches[57], [58]
Sensory evaluation of Germinated brown rice milk i
Effects of heating time and temperature on the GABA content of the germinated rice
Figure 4 3:GABA of GBRM at different thermalize temperature and time (àg/ml)
Figure 4.3 illustrates the retention of GABA after thermalization at temperatures of 70°C, 80°C, and 90°C over durations of 10, 20, and 30 minutes The GABA content is least affected at 90°C, with a decrease from 309.37 ± àg/ml at 10 minutes to 268.16 ± àg/ml at 30 minutes At 70°C, GABA levels show minimal loss, with values of 435.77 ± 9.71 àg/ml, 425.06 ± 14.49 àg/ml, and 422.86 ± 8.09 àg/ml for 10, 20, and 30 minutes, respectively, resulting in a loss of only 12.91 àg/ml In contrast, thermalization at 80°C results in a more significant loss of 31.05 àg/ml over the same duration, with GABA levels decreasing from 435 ± 7.48 àg/ml to 404.17 ± 8.58 àg/ml Overall, the findings indicate that lower thermalization temperatures preserve GABA content more effectively.
The loss GABA during thermalizing process mainly related to the chemical interaction between GABA and other components within the GBRM (Le et al in 2020 found that the GABA content
During the thermalizing process at temperatures of 70°C and 90°C, 29% of rice milk is lost GABA, an amino acid, participates in the non-enzymatic browning process with sugar when heated between 50°C and 90°C for 10 minutes, leading to an increase in Maillard products in heat-treated soymilk In the case of GBRM, starch granules are hydrolyzed by α-amylase into simple sugars Additionally, GBRM is combined with 5% D-glucose to replicate the sweetness of commercial rice milk This mixture influences the non-enzymatic browning process, as GABA interacts with simple sugars, resulting in a noticeable reduction in GABA content.
Thermalizing the GBRM at 80°C for 30 minutes is the most effective method, as it minimizes GABA content loss while also serving as a pasteurization process for rice milk.
Influence of different thickener formulations on the stability of the rice milk
Figure 4 4:Stability (%) of GBRM between the use of hydrocolloids
The stability of the Gelatinized Brown Rice Milk (GBRM) is influenced by the particle size and concentration of starch granules and other components in the solution After 7 days of storage at 5°C, it was observed that hydrocolloids enhance GBRM stability, although a concentration of 0.1% (w/v) showed no significant difference compared to the blank sample Notably, stability increased with thickener concentrations ranging from 0.3% (w/v) to 0.5% (w/v), indicating optimal levels for improving rice milk stability Xanthan gum at 0.5% (w/v) exhibited the highest individual stability at approximately 83% However, combining different hydrocolloids yielded even greater stability, with a Xanthan gum and Pectin mixture achieving nearly 100% stability, while Guar Gum and Pectin resulted in 93%, and a combination of Xanthan Gum and Guar Gum reached 97%.
In the food and beverage industry, rice milk is recognized as an emulsion that consists of various components separated by different phases Over time, rice milk can separate during preservation and production, leading to an unappealing appearance that may deter consumers To enhance the quality of rice milk and prevent separation, the use of hydrocolloids as thickeners is essential for improving sensory appeal and overall product evaluation.
Figure 4 5:Seperate time of GBRM between hydrocolloids (h)
The incorporation of hydrocolloids into rice milk enhances the viscosity and stability of the final product, particularly in germinated brown rice milk Thickeners at a concentration of 0.1% (w/v) do not affect the separation time of the rice milk, as observed with Xanthan Gum, Guar Gum, and Pectin However, increasing the concentration to 0.3% (w/v) yields improved results, with Pectin effectively delaying the separation process for over 3 days, while Xanthan Gum and Guar Gum show separation times of 29 and 30 hours, respectively When all three thickeners are utilized at 0.5% (w/v), further insights into their effectiveness can be explored.
31 concentration, the layer separation of rice milk is delayed to >120 hours These results show the same in the condition of mixing different hydrocolloids to enhance the effect of stability
The particle size in the solution significantly influences the separation rate within the GBRM, with an average size of 2725.9 ± 370.65 nm, as indicated in the accompanying table Particle size analysis using the Zetasizer Pro reveals that this size is still visible to the human eye and is classified as an emulsion droplet, typically exceeding 1 µm Larger particle sizes in an emulsion system facilitate a quicker separation process Additionally, gravitational separation can occur in rice milk, leading to changes in product stability.
Figure 4 6:Viscosity (mPa) of GBRM between different use hydrocolloids and concentrations i
The viscosity of germinated brown rice milk was measured using a Brookefield Viscometer with S61 and S62 readers Results indicate that increasing hydrocolloid concentration enhances the viscosity of the rice milk Individually, a 0.5% concentration of each hydrocolloid exhibited high viscosity at three different rotational speeds The highest viscosity was observed in mixtures of Xanthan Gum with Guar Gum, Guar Gum with Pectin, and Pectin with Xanthan Gum, showing significant differences compared to single hydrocolloid use at concentrations from 0.1% w/v to 0.5% w/v Notably, the combination of Xanthan Gum and Guar Gum increased the viscosity of the rice milk to over 200 mPa, likely due to gel formation between these hydrocolloids and the starch content in the rice milk.
Optimizing processing conditions and understanding the flow characteristics of fluid meals are crucial for achieving positive consumer effects The rheological properties of a fluid are influenced by its chemical composition, processing temperature, and other factors The incorporation of hydrocolloids significantly boosts product viscosity, which correlates with improved stability in rice milk Increased viscosity slows particle and droplet movement in liquids, enhancing the physical stability of GBRM by minimizing destabilization rates.
Determination of the suitable use of thickeners and their effects on the GABA content
Figure 4 7:GABA (àg/ml) content between hydrocolloids and formulation
The results depicted in Figures 4 and 7 demonstrate that varying concentrations of thickeners significantly affect GABA concentration (àg/ml) Specifically, Xanthan Gum at 0.5% w/v (412.23±14.93 àg/ml) and Guar Gum at 0.5% (409.81±10.28 àg/ml) lead to a notable reduction in GABA content when used alone Conversely, Pectin exhibits minimal variation in GABA levels at concentrations of 0.1% (463.23±19.51 àg/ml) and 0.3% w/v (462.60±6.12 àg/ml) The chemical interactions between Xanthan Gum and amino acids, particularly through the Maillard reaction, contribute to the loss of Gamma-amino Butyric acid (GABA), a crucial amino acid in the GBRM Similarly, Guar Gum's mannose and galactose units interact with amino acids, further diminishing GABA content.
The combination of Guar Gum and Xanthan Gum results in the lowest GABA content (403.24±8.60 àg/ml) among the samples, significantly influenced by the properties of both hydrocolloids Other mixtures also demonstrate a reduction in GABA content compared to the individual use of Xanthan Gum, Guar Gum, and Pectin This indicates that utilizing various thickeners for stabilizing the GBRM can lead to GABA loss, which may impact manufacturing costs due to potential chemical interactions, particularly through the Maillard reaction during heat treatment at 80 ºC.
Determination of the preservation parameters of GBRM
Table 4 2: The GABA loss of GBRM preserved at different temperature for 7 days (àg/ml)
Table 4.2 indicates that the preservation of GABA rice milk (GBRM) at temperatures of 5ºC, 10ºC, and 25ºC results in a GABA loss of 43.44±11.33 àg/ml, 42.42±20.83 àg/ml, and 34.93±7.85 àg/ml, respectively, after 7 days Although there are differences in GABA loss across the various storage temperatures, these differences are not statistically significant This suggests that storage temperature does not significantly affect GABA content in rice milk (Le et al., 2020) Therefore, it can be concluded that GABA rice milk can be stored at different temperatures without adversely impacting its GABA content.
Table 4 3: Microbial count of GBRM preserved at different temperature for 7 days
The total microbial count is a crucial factor in determining the consumption of GBRM Cold storage at 5°C is the most effective method for inhibiting microorganism growth, as evidenced by the microbial content reaching 141±20.52 CFU/ml after 7 days, compared to earlier overgrowth at 10°C and room temperature when counts exceeded 100 CFU/ml The predominant bacteria in rice milk are aerobic, particularly Bacillus cereus, which thrive in temperatures between 8°C and 55°C Rice milk's nutrient-rich composition, containing starches and sugars, serves as a food source for these bacteria, leading to toxin production and spoilage According to TCVN 4884-1: 2015, a total aerobic bacteria count must remain below 100 CFU/ml to be considered safe for commercial consumption; exceeding this threshold indicates spoilage and safety concerns.
Table 4 4: pH value of GBRM preserved at different temperature for 7 days
The pH value of germinated brown rice milk (GBRM) decreases over time during preservation, as shown in Figure 4.8 At 5°C, the pH drops from 6.62 to 5.29 over 7 days, while at 10°C, it only decreases slightly from 6.62 to 6.03 Similarly, at room temperature (25°C), the pH decreases from 6.62 to 6.01 within 3 days Higher storage temperatures promote the growth of harmful microorganisms, which is why preservation at temperatures above 5°C is less effective At 5°C, most harmful microorganisms are inhibited, allowing GBRM to meet food safety standards for consumption.
Conclusion and recommendations
Conclusion
This study investigates the impact of soaking treatments on the GABA content of germinated rice and examines how various processing parameters affect sensory quality, stability, pH value, and microbial count Soaking rice for 8 hours at a 1:10 rice-to-water ratio emerged as the optimal method for industrial production of germinated brown rice milk (GBRM), effectively extracting desirable GABA levels while minimizing time and costs The incorporation of a thickening mixture of Guar gum and Pectin yielded the highest GABA retention, whereas a combination of Xanthan gum and Guar gum provided superior stability and viscosity These findings indicate that GBRM can be formulated to minimize GABA loss while maintaining stability For effective preservation, storing GBRM at 5°C is recommended, as it ensures minimal GABA degradation and safety for consumption, aligning with food preservation standards.
Recommendations
This study examines the impact of various thickeners and high-temperature treatment on GABA content over a 7-day storage period Future research should explore alternative food additives and heat treatment methods, such as microwave and low-temperature sterilization, to reduce GABA loss Additionally, investigating new storage techniques could help prevent the natural degradation of GABA during storage.
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GBRM: Germinated brown rice milk
APPENDIX 2: GABA CONTENT BETWEEN THERMALIZATION TEMPERATURE AND DURATION
APPENDIX 3: SENSORY BALLOT FOR EVALUATION OF GBRM
APPENDIX 4: STABILITY OF GBRM USED DIFFERENT HYDROCOLLOIDS
APPENDIX 5: SEPARATE TIME OF GBRM USED DIFFERENT HYDROCOLLOIDS
APPENDIX 6: VISCOSITY OF THE GBRM USED DIFFERENT HYDROCOLLOIDS MEASURED AT 50 RPM
APPENDIX 7: VISCOSITY OF THE GBRM USED DIFFERENT HYDROCOLLOIDS MEASURED AT 60 RPM
APPENDIX 8: VISCOSITY OF THE GBRM USED DIFFERENT HYDROCOLLOIDS MEASURED AT 100 RPM
APPENDIX 9: GABA CONCENTRATION LOSS DURING PRESERVATION
Temperature of preservation GABA loss (àg/ml)
APPENDIX 10: GABA CONTENT BETWEEN DIFFERENT SOAKING TIME AND TEMPERATURE
APPENDIX 11: GABA CONTENT BETWEEN DIFFERENT HYDROCOLLOIDS
Sample GABA content (àg/ml)
APPENDIX 12: GABA STANDARD CURVE PREPARATION
APPENDIX 14: MICROBIAL COUNT RESULT DURING PRESERVATION AT 5C
APPENDIX 15: MICROBIAL COUNT RESULT DURING PRESERVATION AT 10C
APPENDIX 16: MICROBIAL COUNT RESULT DURING PRESERVATION AT 25C i