Research rationale
Tofu, a significant food derived from soy protein, holds a vital place in Southeast Asian cuisine due to its impressive nutritional value and digestibility Recognized for its health benefits by the FDA in 1999, tofu has seen a surge in popularity in Western countries in recent years, reflecting a growing awareness of its nutritional advantages.
Tofu and soy products are associated with numerous health benefits, including a potential reduction in chronic diseases such as cancer, heart disease, and osteoporosis Research indicates that soy protein, rich in isoflavones and isoplavolesterol, may help combat atherosclerosis and lower total cholesterol, LDL, and triglycerides compared to animal proteins Additionally, the antioxidant properties of isoflavones and proteins in tofu protect against lipid oxidation Despite its popularity among both urban and rural populations in Vietnam, tofu production remains largely small-scale, utilizing outdated technology and lacking quality registration This results in a short shelf life of just 1-2 days, limiting the market potential for tofu products.
3 causes waste product, but also limits the scope of the distribution and the time it takes to commercialize the product
The protein coagulation process in tofu primarily involves food-safe chemicals like calcium sulfate (CaSO4), magnesium chloride (MgCl2), citric acid, and calcium chloride (CaCl2) (Murugkar, 2015) However, some tofu manufacturers utilize impure chemicals, resulting in metal residues in the final product.
Lactic bacteria are gaining significant attention among scientists due to their numerous benefits in food technology The organic compounds generated during lactic fermentation are recognized for their antibacterial properties Consequently, research is increasingly focused on utilizing lactic fermentation and its extracts as biological preservatives to effectively reduce mycotoxins in food, yielding impressive results.
Therefore, I conducted the topic: " Isolation of lactic bacteria apply in tofu producing process".
Research objective
Isolation and selection of lactic acid bacteria with good fermentation ability and application in tofu production process as a coagulant
Detail goals
- Isolation some strains of lactic acid bacteria
- Selection of bacteria with good fermentation ability apply for tofu production
Limitations
Limitation that are expected to be encountered throughout the study
- Language barrier: Since this report is conducted in English, so the study would have some obstacles due to the difference of language
The research is conducted at the Faculty of Food Biotechnology and Food Technology at Thai Nguyen University of Agriculture and Forestry, where there is a lack of specialized equipment and machinery necessary for the research process.
REVIEW
OVERVIEW OF SOYBEAN
Soybeans are scientifically known as Glycine max Merril According to
Phạm Văn Thiều (1993) in the book "Soybean Plant, Cultivation and Product Processing Techniques" describes soybeans as short-term legumes, with a growth period of 80 to 150 days The plants typically reach heights of 30 to 80 cm and are characterized by their relatively upright growth and fewer branches compared to other legumes Each soybean plant can produce nearly 400 fruits, with each fruit containing 1 to 7 seeds and measuring about 4 to 6 cm in length Soybean seeds come in various shapes, including round, oval, long circle, and flat circle, with colors ranging from yellow-green to gray and black, though yellow is the most common The soybean consists of three parts: the shell, cotyledons, which serve as nutrient reserves, and the embryo.
Unlike cereal grains, soybean seeds lack an aleurone layer, with the endosperm and embryo existing separately The entire soybean is essentially a large embryo encased in a seed coat, resulting in lower starch content compared to other legumes, while significantly higher levels of protein and lipids are present.
2.1.2 Acreage, yield and demand for soybeans
2.1.2.1 Production situation in the world
Soybeans originated in East Asia, yet approximately 60% of global soybean production occurs in the Americas, with the United States and Brazil leading in output Recent data indicates that Brazil has overtaken the US, producing 124 million tons of soybeans in the first half of 2020, with nearly two-thirds of this production destined for export Other significant soybean-producing nations include Argentina, China, India, Paraguay, and Canada For a detailed view of soybean export volumes from major countries between 2017 and the first half of 2020, refer to Table 2.1.
Table 2.1 Soybean export volume of some major countries in the world in the crops of 2017/2018, 2018/2019 and 2019/2020 (thousand tons)
(Source: FAS/USDA – statista) 2.1.2.2 Production situation in Vietnam
Currently, soybean growing are forming in 4 concentrated areas
Northern midland and mountainous provinces
The Red River Delta region
The Mekong River Delta region
Soybean plants exhibit rapid growth and adaptability, making them suitable for multiple cropping seasons throughout the year, including winter-spring, spring, summer-autumn, and spring-summer In Vietnam, soybeans are primarily cultivated in the mountainous and midland regions of northern provinces, such as Cao Bang and Son.
La, Bac Giang accounts 40% of the total area of the country In addition, soybeans are also grown in some regions such as Dong Nai, Daklak, Dong Thap
Each year, Vietnam expands its agricultural land by approximately 100,000 hectares, primarily for winter crops, yielding around 160,000 tons in 2017 This production satisfies only 8-10% of the country's soybean demand, which has been growing at an average rate of 53% As a result, Vietnam continues to rely on soybean imports, predominantly sourcing from markets such as China.
Cambodia, Thailand, Canada and the United States In particular, Brazil is the largest soybean supplier to Vietnam with soybeans imported from this market in
2012 reaching 584.6 thousand tons Situation of soybean production in Vietnam from 2010 to 2017 can be observed in table 2.2
Table 2.2 Soybean production in Vietnam from 2011 to 2017
(Source: General Statistics Office of Vietnam, * FAS estimates)
Cultivated area (thousand hectares) 197,8 181,1 120,8 180 200 100,8 94 100 Yield (tons /hectare) 1,51 1,47 1,45 1,5 1,5 1,45 1,57 1,57 Total quantity (thousand tons ) 298,6 266,9 175,3 270 300 146,4 147,5 157
Table 2.3 Production, supply and demand of soybeans in Vietnam
(Source: Vietnam General Statistics Office, Global Trade Atlas, USDA adjusted statistics)
As the demand for soybeans continues to rise, domestic production is insufficient to satisfy the overall need, particularly for tofu products Consequently, the soybean supply heavily relies on imports to bridge this gap.
Soybeans are unique among legumes due to their lower starch content, but they stand out for their significantly higher levels of protein and lipids In fact, soybeans boast the highest protein content compared to other commercial legumes (Yaklich 2001) [27].
Soybean seeds have a protein content ranging from 39.5% to 50.2% and an oil content between 16.3% and 21.6% on a dry matter basis Additionally, they contain minor components such as phospholipids, vitamins, minerals, trypsin inhibitors, phytates, oligosaccharides, and isoflavones.
Table 2.4 Chemical composition of some kind of beans
Content by percentage by weight of dry matter Ash Cellulose Sugars Starch Protein Lipid Đậu Hà Lan
Table 2.5 Chemical composition of soybean
Table 1.5 illustrates that in soybean seeds, the protein is predominantly concentrated in the endosperm and embryo, whereas the seed coat contains lower protein levels and a higher carbohydrate content.
Table 2.5 illustrates that soybean seeds primarily concentrate protein in the endosperm and embryo, while the seed coat has lower protein levels and higher carbohydrate content Soy protein constitutes a significant portion of the seed and is made up of essential amino acids, although it has low levels of methionine and tryptophan The remaining amino acids in soy protein are comparable to those found in other key products.
Soy protein consists primarily of globulin, which makes up 85% to 95% of its composition, although variations exist among different soybean types Additionally, soybeans contain small amounts of albumin, prolamin, and glutelin The total protein content in soybeans ranges from 29.6% to 50.5%, with an average protein percentage between 36% and 40%.
Soy protein is almost identical to the protein of an egg The amino acid content of soybeans when compared to other foods is shown in Table 2.6
Table 2.6 Non-substituting amino acids in soybeans compares to other important foods (g / 100g protein)
Amino Acid Soybean Egg Beef Milk Rice Necessary value
Soybeans contain a lipid content ranging from 13.5% to 24%, with an average of 18% of their dry weight, primarily composed of glycerides and lecithin These glycerides are rich in unsaturated fatty acids, particularly 50-60% linolenic acid (C18-2), which contributes to their high biological value However, this high lipid content also makes soybeans prone to oxidation, resulting in spoilage during storage.
Soy lecithin makes up 3% of the grain weight A complex phosphatide, used as an emulsifier, and antioxidant in food processing
Carbohydrates represent approximately 34% of the dry weight of grains, with starch content being minimal They are categorized into two types: soluble and insoluble, with water-soluble carbohydrates comprising only about 10% of the total For detailed information on the carbohydrate content of soybean seeds, refer to Table 2.7.
Table 2.7 Carbohydrate components in soybean
Soybeans are rich in essential vitamins necessary for body development, although they have low concentrations and can easily lose these nutrients during processing For a detailed breakdown of their vitamin composition, refer to Table 2.8.
Table 2.8 Vitamin content in soybean
Folic acid 1,9 mg/g Vitamin PP 2,3 mg%
The mineral content accounts for 5% of the dry weight of the soybean seed
In which, notably calcium, phosphorus, manganese, zinc, iron Soybeans are rich in iron and zinc The content of these minerals is shown in Table 2.9
Table 2.9 Mineral contents in soybean
Soybeans are rich in various enzymes that play crucial roles in biochemical processes Key enzymes include lipase, which hydrolyzes glycerides into glycerin and fatty acids; phospholipase, responsible for hydrolyzing ethers to acetic acid; and lipoxygenase, which catalyzes hydrogen transfer in fatty acids Additionally, soybeans contain amylase, comprising both α-amylase and β-amylase, as well as urease, contributing to their nutritional and functional properties.
OVERVIEW OF TOFU
Tofu, a soft cheese-like product made by coagulating soy milk protein, is a staple in Asian cuisine and is rapidly gaining popularity in American and European markets.
Tofu is a versatile ingredient that can be prepared through various cooking methods, including frying, baking, boiling, and steaming There are three main types of tofu available: hard, soft, and silken, each differing in water content and texture This variety allows producers to create a range of tofu structures, catering to diverse culinary needs.
Hard tofu is ideal for cooking methods like stir-frying and baking due to its ability to maintain shape, and it boasts the highest protein and lipid content among tofu varieties In contrast, silken tofu has a creamy, custard-like texture and requires no additional flavoring or spices when prepared Typically sold cold, silken tofu is packaged in tubes filled with water or vacuum-sealed for freshness.
Tofu is a highly nutritious food rich in minerals like calcium, iron, and vitamin B, while being low in sodium and cholesterol-free This soy protein gel has gained popularity as a healthy dietary option The production of tofu is increasingly shifting from manual methods to automated processes, utilizing advanced equipment primarily developed in Japan.
Tofu production begins by soaking soybeans to extract soy milk, which is then boiled A coagulant, typically calcium chloride (CaCl2) or magnesium chloride (MgCl2), is added to the hot milk to facilitate coagulation The resulting solid mass is then processed into various forms of tofu, predominantly in block shape.
2.2.1 Process of producing tofu from natural sour water [1]
(Công nghệ sản xuất mì chính và các sản phẩm lên men cổ truyền (1))
2.1 Traditional tofu production process in Vietnam
The wet grinding method involves a crucial soaking phase where beans absorb water and swell, allowing bipolar water molecules to interact with proteins, lipids, carbohydrates, and cellulose This process occurs in two stages: first, the solvate process, where the bonds in soybeans remain intact, followed by the hydration process, in which water molecules break molecular bonds, transforming the beans into a flexible colloidal state Key factors influencing the soaking process include soaking time, the amount of soaking water, and immersion temperature.
- Soaking time: outdoor temperature from 15 ÷ 25°C, soaking 5 ÷ 6 hours; outdoor temperature 25 ÷ 30°C, soaking 3 ÷ 4 hours
Soaking soybeans at high temperatures accelerates the swelling process but limits the seeds' swelling capacity As a result, the components in the beans remain in a coagulated state rather than forming a colloidal solution, making them harder to dissolve The optimal soaking temperature for beans is between 20°C and 25°C.
To achieve optimal swelling and low acidity in beans, a soaking ratio of 1 part beans to 2.5 parts water is recommended This method ensures that the beans reach an ideal moisture content of 55 to 60% by the end of the soaking phase.
Grinding is a mechanical process that breaks down cells to release proteins, lipids, and carbohydrates, which can then be transformed into suspensions with the addition of water The key factor in this process is the amount of water used; insufficient water leads to excessive friction and temperature rise, resulting in protein denaturation and reduced solubility Conversely, adding too much water increases the number of dissolved substances but complicates subsequent stages For optimal results, the ideal water-to-bean ratio for grinding should be 1:6.
After grinding, a suspension is created that includes a colloidal solution and water-insoluble solids To separate the colloidal solution from the solids, it's essential to rinse the solids with water, ensuring that the amount used is minimal The filtration process consists of two key steps: refining and crude filtration.
After filtration, it is crucial to heat the milk solution immediately to effectively deactivate the enzyme trypsin and eliminate the toxin aflatoxin, while also killing harmful microorganisms This heating process deodorizes any fishy odors and disrupts the solvated layer, facilitating the coagulation of milk molecules To achieve optimal soy milk quality, it is recommended to boil 100 liters of milk within 5 to 10 minutes Continuous stirring during boiling is essential to prevent the milk solution from burning.
After boiling the soy milk must precipitate immediately The protein
The isoelectric region at pH 19 plays a crucial role in the precipitation of proteins in milk, which is typically heated to temperatures between 95°C and 100°C to induce thermal denaturation Various agents can facilitate protein precipitation, including natural sour water, CaCl2, CaSO4, acetic acid, and lactic acid, with natural sour water being the most effective option However, successful precipitation using sour water requires considerable expertise Key conditions for the precipitation of soy milk must also be met to achieve optimal results.
The temperature of the soy milk solution when precipitating is> 95°C;
pH of the aqueous solution when precipitation is greater than 6;
The pH level of sour water plays a crucial role in precipitation, as a high pH requires a larger volume of sour water, while a low pH decreases protein recovery efficiency To optimize this process, slowly introduce sour water to the milk solution at 95°C in three phases, starting with the addition of half of the sour water in the first phase.
After 3 minutes add half of the remaining sour water;
After 3 minutes, add the remaining sour water
Usually, the amount of sour water accounts for 20 to 22% of the bean milk to be precipitated
2.2.2.5 Squeeze the tofu and soak into water
To create tofu, start with tofu curd after precipitation, and place it into a mold The ideal pressing temperature for the curd ranges from 70 to 80°C; temperatures below 60°C will prevent the curd from sticking together and forming a solid shape Typically, the pressing process lasts for about 10 minutes.
After pressing the tofu, carefully remove it from the mold and cut it into your desired sizes To ensure a stable structure, soak the tofu in water for an extended period, which will also enhance its flavor.
FUNDAMENTAL OF THE GEL PROTEIN FORMATION PROCESS OF
The key step in achieving the desired texture of tofu is the formation of protein gel Native soy proteins do not gel on their own; they require heat denaturation and subsequent coagulation to create tofu (Liu, 1997) The process involves thermal denaturation, ordering, and gel formation, which are crucial for ensuring that all proteins are evenly dispersed within the gel network.
The production of tofu involves a crucial gel-forming process where soybean protein undergoes thermogenesis, transforming soy milk into a structured gel that ultimately becomes tofu.
Thermal denaturation serves to expand the protein structure, transitioning it from a compact form to a more open and diffuse configuration This heating process reveals the internal structures of protein molecules, exposing critical functional groups such as –SH, hydrophobic regions, carbonyl groups, amine groups from peptide bonds, and amide groups in side chains These exposed functional groups play a significant role in influencing the protein's network structure (Wang and Damodaran, 1991).
After dissociation and then regroup during the heat denaturation the protein molecules are transformed into fibers Interaction of protein molecules, fibers in a certain order form the three-dimensional network
The mechanism of soy milk protein gel formation is determined mainly by temperature and consists of two main processes: dissociation and aggregation
21 different Gel formation in tofu production is affected by both glycinin and conglycinin fractions If the glycinin ratio is higher than conglycinin, the tofu gel will form harder
2.2 Different gel network structures of protein 2.3.2 Factors affecting
Protein concentration plays a crucial role in determining the type and properties of soy milk protein gel To achieve gel formation, soy milk must contain at least 8% protein, with higher globulin concentrations than gelatin Additionally, a high glycinin content facilitates gel formation, while low glycinin levels can hinder it due to separation tendencies The mechanical strength of the gel is directly influenced by protein concentration, as greater strength correlates with an increased number of cross-links in the protein chain Thus, there is a linear relationship between the mechanical strength of the gel and its protein concentration.
Temperature significantly impacts the quaternary structure of soy protein, particularly affecting glycinin and β-conglycinin, which denature at 85-95°C and 65-75°C, respectively Glycinin contains a large disulfide bridge, contributing to its unique properties Heating soy protein above the minimum denaturation temperature necessary for gel formation alters the gel's rheological properties, while lower temperatures require extended time for gel formation, resulting in weaker gels Insufficient heating fails to create a robust three-dimensional network, and excessive high temperatures can lead to protein metamorphosis, preventing gel formation altogether.
Adding a 2% NaCl solution to soy milk enhances the formation of gel by increasing the ratio of glycin and conglycin However, at a concentration of 10%, gel formation is inhibited Low concentrations of NaCl neutralize charges, promoting gel formation, while high concentrations disrupt protein structure and increase hydrophobic interactions, ultimately preventing gel formation.
The protein denaturation process is influenced by pH levels, affecting the interactions between proteins and solvents (Renkema, 2000) To attain the optimal balance between denaturation and recombination, as well as the attraction and repulsion of adjacent protein chains, pH adjustment is essential Notably, when the pH exceeds 12, the gel formation process is entirely inhibited.
At high alkaline pH values, polypeptide chains acquire a negative charge, leading to electrostatic repulsion that can destabilize protein interactions during gel network formation and ultimately reduce gel strength Conversely, at neutral pH, the presence of positively charged groups enhances energy levels, promoting stronger gel formation.
Soy protein is categorized into four segments: 2S, 7S, 11S, and 15S, with the 7S and 11S fractions being the primary components The 7S fraction, known as conglycinin, and the 11S fraction, referred to as glycinin, together comprise approximately 65% to 85% of the total protein content found in soy seeds.
Glycinin, an oligoprotein, is composed of six monomers arranged in a hexagonal structure, consisting of two trimers, each containing three monomers This specific arrangement is illustrated in the molecular structure depicted in section 2.3 Additionally, globulin, classified as either 7S or 11S, comprises 12 lipophilic subunits, which include six acidic subunits (A) and six basic subunits.
"subunit" (B) The "sub the unit" are linked together by a disulfide bridge
2.3 The molecular structure of Glycinin
β-conglycinin is a glycoprotein that constitutes approximately 35% of the protein content in seeds and contains nearly 5% carbohydrates Its structure is divided into three main subunits, known as α, α', and β, which are organized into distinct sub-fractions.
2.4 The molecular structure of Conglycinin
The subunits are linked together through hydrophobic, hydrogen-linked interactions without any disufite bonds (Thanh and Shibasaki,1978)
Using Ca2+ as a coagulant in soy milk protein precipitation can be effective, but it may introduce impurities in tofu production An alternative approach is to utilize fermentation solutions to lower pH, with lactic acid bacteria (LAB) being a well-known example LAB is widely recognized in the food industry for its beneficial effects on both food quality and consumer health.
Lactic bacteria, which are Gram-positive, non-spore-forming, and non-mobile, play a crucial role in sugar fermentation to produce lactic acid This group falls under the family Lactobacillaceae and is divided into four distinct genera.
Streptococus, Pediococcus, Lactobacillus and Leuconostoc This group of bacteria has many different shapes, including short or long bacillus shaped in single or
Lactic acid bacteria can be found in various forms, including double (in pairs) or in series, as well as spherical (cocci) or rod-shaped (bacilli) Typically, the diameter of lactic cocci ranges from 0.5 to 1.5 micrometers These bacteria often form colonies that are small, round, and glossy, exhibiting colors such as milky white or cream yellow Notably, some colonies are larger, round, and milky convex in shape, often accompanied by a distinct acidic odor.
2.4.2 Common features of lactic acid bacteria
Lactic acid bacteria exhibit notable morphological differences, yet they share a relatively uniform structure These gram-positive, non-motile bacteria do not form spores and have a limited capacity for synthesizing various substances Capable of both anaerobic and aerobic fermentation, they demonstrate a high tolerance for acidic environments (Whittenbury, 1964).
OVERVIEW OF HYDROPEROXIDE AND BACTERIOCIN DURING
Lactic fermentation effectively reduces carbohydrates while producing various organic compounds with antimicrobial properties, primarily lactic, acetic, and propionic acids Numerous lactic acid bacteria can synthesize additional antibacterial compounds, which exhibit low molecular weight and possess unique characteristics such as antimicrobial activity at low pH, temperature stability, a broad spectrum of efficacy, and solubility in acetone The fermentation medium is enriched with these diverse organic substances following the lactic fermentation process.
Bacteriocin, a significant antibacterial compound, is extensively studied and utilized as a biological preservative in food due to its heat-stable properties that effectively inhibit Gram-positive bacteria (Karpinski, 2016) Additionally, organic acids, particularly lactic acid produced during fermentation, contribute to antibacterial effects by lowering pH Hydroperoxide and other substances also play a role in this antibacterial action Consequently, lactic fermentation fluid, used as a tofu precipitation agent, possesses natural antibacterial properties, allowing for prolonged storage of tofu products without the need for chemical preservatives, ensuring consumer safety.
Hydroperoxide (H2O2) is a byproduct of lactic fermentation, known for its strong oxidizing properties that exert a bactericidal effect by oxidizing bacterial cell membranes and proteins This process can generate atomic oxygen, creating an anaerobic environment that is inhospitable to specific microorganisms Lactic acid bacteria synthesize hydroperoxide in the presence of oxygen, contributing to its formation during fermentation.
Lactic acid bacteria require a source of heme to produce catalase, which is essential for the removal of hydroperoxide Without heme, these bacteria struggle to eliminate hydroperoxide effectively, as alternative removal systems are less efficient, resulting in hydroperoxide accumulation (Ouwehand, 2004).
Bacteriocin is an antibacterial peptide produced by bacteria to combat other bacterial strains (Karpinski, 2016) Bacteria capable of producing bacteriocin can resist its effects, making them unique in their defense mechanisms Importantly, bacteriocin is non-allergenic and does not pose health risks to humans; it is also rapidly hydrolyzed by proteases and lipases Typically, bacteriocins produced by lactic acid bacteria are positively charged protein molecules, ranging from 30 to 60 amino acids in size, with a high isoelectric point, which enables them to inhibit closely related bacterial species These bacteriocins are found in various groups of lactic acid bacteria, including Lactobacillus, Lactococcus, Enterococcus, Streptococcus, Leuconostoc, and Pediococcus, with Lactobacillus and Lactococcus being the most significant producers Bacteriocins have been shown to inhibit harmful bacteria such as Clostridium botulinum, Bacillus cereus, Bacillus alcalophilus, and Listeria monocytogenes.
OVERVIEW OF TOFU PRESERVATION
The final step in tofu production involves packaging and preservation, which significantly influences the taste, quality, and shelf life of the tofu The choice of packaging materials and storage technologies plays a crucial role in maintaining the product's integrity and freshness.
Tofu products, due to their high moisture and protein content, create an ideal environment for microbial growth Consequently, even when refrigerated, their shelf life is limited to just a few days.
Extending the shelf life of tofu products remains a crucial topic in food preservation Currently, various methods are employed to preserve tofu, including the use of preservation chemicals and advanced packaging technologies.
In general, prolonging shelf life can be divided into two parts
2 Apply storage preservative during or after packaging
These methods of preservation include physics, chemistry, and a combination of
Together with using lactic bacteria, 2 preservation method will be used to prolong the shelf life of tofu
Modified atmosphere packaging (MAP) involves sealing food in an initially fixed gas composition that changes over time This method replaces air in food packaging with a controlled mixture of gases such as carbon dioxide, oxygen, and nitrogen The purpose of MAP is to alter the gas environment surrounding the food, thereby preserving its physical, chemical, and biological quality and preventing deterioration.
MAP has been studied with tofu Stoops, Maes, Claes, and Van Campenhout
A study conducted in 2012 examined the growth of Pseudomonas in tofu products under modified atmosphere packaging (MAP) and found that controlling carbon dioxide and oxygen levels in refrigerated products was ineffective in eliminating Pseudomonas spoilage Another investigation utilized a CO2 and N2 mixture (CO2: N2 = 3:7) with flushing or vacuum compensation, while tofu packed in air served as a control The findings revealed that the microbial count in air-packed tofu was one to four log cycles higher than that in MAP after 10 days of storage, with MAP successfully inhibiting microbial growth for up to 14 days (Van Campenhout, Maes, & Claes).
In summary, MAP has been successfully used for shelf life extension and freshness preservation of tofu products
Food freezing technology is used as a food preservation method It can increase the storage time and extend the shelf life of food (Kobayashi, Ishiguro,
Ozeki, Kawai, & Suzuki, 2020) Frozen tofu is a delicious and famous Asian food made by freezing soft or firm tofu (Ji et al., 2017).
RESEARCH SITUATION WORLDWIDE AND IN VIETNAM
In 2020, Kay Huyn Joo and colleagues explored the viability of trimagnesium citrate (TMC) as an alternative coagulant for tofu, benchmarking it against traditional industry coagulants Their study assessed various factors, including yield, water-holding capacity (WHC), texture profile analysis (TPA), confocal microscopic analysis, and sensory evaluation of both raw and cooked tofu produced with different coagulants The findings revealed that while TMC did not affect the yield, it positively influenced the textural properties and enhanced the sensory quality of the tofu.
Yin and colleagues investigated the effects of fermentation with Actinomucor elegans on the phenolic components, antioxidant activities, and nutritional compounds of tofu The study found a significant increase in both total and soluble phenolic content, alongside a decrease in insoluble phenolic content after fermentation Fermented tofu exhibited higher antioxidant activities compared to its unfermented counterpart Metabolomic analysis indicated a substantial enhancement in the nutritional composition of tofu, including carbohydrates, alcohols, fatty acids, organic acids, inorganic acids, and amino acids during fermentation These results highlight that fermentation with A elegans can markedly improve the nutritional and functional properties of tofu.
In 2020, Elvira and colleagues explored the integration of machine learning and artificial intelligence in their research on food preservation They specifically evaluated the effectiveness of Plasma Activated Water (PAW) as an immersion solution, alongside traditional chemical preservatives and natural microbiological strains.
35 these results evidence that PAW is a promising non-thermal technology which can facilitate the control of pathogenic microorganisms on tofu while retaining its physical and functional properties
Tofu, a traditional and popular food, has not been extensively studied in Vietnam A significant study conducted in 2014 by Nguyen Thi Minh Nguyet and Pham Thi Kim Ngoc explored the impact of coagulation agents on tofu's recovery efficiency and quality Their findings indicated that sour water can be effectively used to produce safe, high-quality tofu, revealing unique properties in tofu made with plaster.
METHOD
RESEARCH SUBJECT
Soybeans are scientifically known as Glycine max Merril
Soybeans choose good quality (round beans, uniform, light yellow color, poor quality seeds such as beetles, little damage, low ratio of flat seeds, low cracked seeds)
Soybeans were purchased in Thai Nguyen
Using lactic bacteria strains isolated from fermented sour products such as pickles, yogurt, fermented soy milk
3.2 Equipments and chemicals required for research
Table 3.3 Laboratory instruments Number Laboratory instruments Origin
3.3 Location and time period of the research
- Location: Faculty of Biotechnology - Food Technology, Thai Nguyen University of Agriculture and Forestry
Content 1: Isolation of some strains of lactic acid bacteria that can be used in tofu production
Content 2: Selection of bacteria with good ferment ability for application in tofu production
3.5.1 Content 1: Isolation of some strains of lactic acid bacteria that can be used in secondary production
3.5.1.1 Method of isolation and selection of lactic bacteria
To cultivate lactic acid bacteria from yogurt and fermented soy milk, a sample was mixed with 20 mL of solution and added to 100 mL of MRS broth medium The mixture was incubated at 37°C for 24 hours while being shaken at 150 rpm.
After diluting the incubation medium to a concentration of 10^-4, 100 µL was spread onto MRS agar plates and incubated at 37°C After 48 hours, characteristic colonies were observed and selected for repeated inoculation on MRS agar until homogeneous colonies were achieved.
3.5.1.2 Determination of morphological, physiological and biochemical features
- Characteristics of colony morphology and bacterial cells: The isolated colonies were examined for cell morphology under the microscope on the oil objective lens X100
- Morphological, physiological and biochemical characteristics: Check some characteristics of lactic acid bacteria
3.5.2 Content 2: Selection of bacteria with good ferment ability for application in tofu production
3.5.2.1 Experimental set up test for soy milk fermentation
Prequalified strains of lactic acid bacteria were incubated to increase the biomass in 10 ml of MRS broth for 24 hours at 37 ° C
Prepare the soy milk solution (soybeans: distilled water = 1: 2.5) Pour into each glass jar 50 mL milk solution Afterward, add 5 ml of lactic bacteria strains and incubate at 41°C for 6-7 hours
The treatments were performed 3 times
3.3.5.2 Tofu production efficiency using lactic bacteria
The optimal pH for precipitating soy milk protein was established through prior experiments A strain with rapid fermentation capabilities and favorable sensory evaluation for soy milk was selected to produce tofu Subsequently, samples were taken to assess production efficiency, following the outlined experimental arrangement.
Figure 3.1 Tofu production process using lactic acid bacteria
1 Indicate the quantity of total aerobic bacteria
The objective of this study was to evaluate hygiene standards in tofu processing and storage, while also examining the antibacterial properties of tofu made with lactic acid bacteria Two parallel samples were analyzed: one tofu sample produced using lactic acid bacteria and another produced with plaster.
The method of enumeration of total aerobic bacteria is specified according to TCVN 5165 - 90 (Appendix 4)
Percentage of fermented soy milk used = 20%
Figure 3.2 Process of enumeration of total aerobic bacteria
Coliforms are a diverse group of Gram-negative, non-spore-forming bacteria that can ferment lactose and produce gas within 48 hours under suitable culture conditions This group includes various species such as E coli, Citrobacter, Klebsiella, and Enterobacter, and can thrive in both aerobic and anaerobic environments.
The purpose of this study is to evaluate the hygienic quality of water and the sanitary conditions in food processing, specifically assessing fecal pollution in water sources and monitoring fluctuations of two bacterial groups throughout production and storage Experiments were conducted using two tofu samples, employing enumeration methods for Coliforms and Fecal coliforms as outlined in TCVN 4882: 2007 (Appendix 5).
From the above dilutions, transfer 100 μl of sample to a Petri dish containing TGA medium (2 dishes each)
Count the colonies growing on the plate
Result: Total number of aerobic bacteria in the sample (CFU / g)
Prepare sample: 1g of tofu + 9ml of distilled water
Figure 3.3 Process of enumeration of Coliform
3 Indicate the quantity of total mold
Principle: Culture media containing inhibitors of bacteria (antibiotics such as Oxytetracylin or Chloramphenicol) are cultured at 30 ± 10C under aerobic conditions after 48 - 72 hours (Appendix 6)
Figure 3.4 Process of enumeration of mold 3.5.3 Sensory evaluation (Sensory evaluation by the method of scoring TCVN
For tofu, to assess the sensory quality, the assessment was conducted through the following four criteria: smell, taste, state, and color
The sensory evaluation of products adheres to Vietnamese standards (TCVN 3215 - 79), utilizing a 20-point scale with six levels ranging from 0 to 5 In this system, the maximum score for an indicator is 5, while the minimum is 0 Each inspector's evaluation is based on the documented results.
From the above dilutions, transfer 100 μl of sample to a Petri dish containing YGC medium (2 dishes each)
Count the colonies growing on the plate
The total count of aerobic bacteria in the sample is measured in CFU/g To prepare the sample, combine 1g of tofu with 9ml of distilled water After obtaining the results, compare them against the established description and criteria, and assign a score using an integer.
When multiple testers evaluate a product (with N being an odd number), the average score is calculated as the mean of the N testers' scores, rounded to two decimal places The weighted average point for each indicator is determined by multiplying the average score of that criterion by its corresponding importance coefficient.
Common point is the total weighted scores of all sensory parameters The six rating ranks are equivalent to the description content Vietnamese standard 3215 -
79 specifies the quality grades for products that have common points and weightless points for some corresponding criteria
Table 3.4 Quality level specified standards
Requirement about average score (without important coefficient)
Excellent 18.6 ÷ 20 Important criteria have higher than 4.7 score Good 15.2 ÷ 18.5 Important criteria have higher than 3.8 score Fairly good 11.2 ÷ 15.1 Each criteria have higher than 2.8 score
Bad 7.2 ÷ 11.1 Each criteria have higher than 1.8 score Very bad 4.0 ÷ 7.1 Each criteria have higher than 1.0 score
To meet the quality requirements (medium grade), the average score without important coefficient for each sensory criteria is 2.8 and the average score is at least 11.2 for each product
Color 5 Ivory white crust, milky white cut, uniform color, without any strange color spots on the bean, water escapes clear, when frying is even yellow
4 The crust and inside coat are ivory-white, uniform color, without any strange spots on the surface of the bean, the water escapes clear, when frying is even yellow
The crust and inner coat of the beans exhibit a uniform opaque yellow color, free from any unusual spots When water is extracted, it appears slightly cloudy, and during frying, the beans maintain an even yellow hue.
The crust should appear ivory white or opaque yellow, free from any unusual color spots When frying, the water may become slightly opaque and yellow, indicating uneven cooking, with some areas showing lighter colors.
1 The crust color is not uniform, the surface is a bit glossy, due to the viscous layer coming out, slightly opaque water escapes
0 The crust is black, white, speckled with pink color due to the development of mold, the water coming out have the color of rice water
Odor 5 The characteristic aroma of cooked soybeans, without any burning, sour, or any strange smell
4 The smell of beans fades, appears a burning odor, no smell of sour, strange smell
3 Clear burning smell, no sour odor
2 Clear burning smell, slightly sour
1 Clear burning smell, much sour
Taste 5 Typical taste of cooked soybeans , with no sour, acrid taste and have aftertaste
4 Typical taste of cooked soybeans , with no sour, acrid taste and have no aftertaste
3 Typical taste of cooked soybeans , a bit sour and acrid taste
2 Typical taste of cooked soybeans , have sour and acrid taste
1 Sour and acrid taste, no more typical taste of cooked soybeans
The product has an intensely sour and acrid flavor, lacking the typical taste associated with cooked soybeans It features a smooth crust without any cracks, and when cut, it reveals soft texture and elasticity Additionally, the product maintains a slightly rough surface and does not break apart when fried, ensuring a satisfying eating experience.
4 Smooth crust, no cracks, smooth cuts, a little tough when eating, when pressing lightly by hands show elasticity, slightly rough, not broken when frying
3 Smooth crust, no cracks, smooth cuts, a little tough when eating, when pressing lightly by hands show no elasticity, slightly rough, not broken when frying
2 Smooth crust, no cracks, cuts are no longer smooth, hard to eat, broken when frying
1 The surface is not smooth, the cuts are not smooth, the structure is broken when frying
0 Too hard or too soft, the structure is broken when frying
A sensory evaluation was performed three times, each involving the preparation of two distinct tofu samples produced at different times The sensory panel assessed these samples using a sensory description scorecard, with each panel member independently evaluating and documenting their results in the sensory assessment.
- Determine the pH index with a pH meter according to TCVN 6492: 1999
- Method of sensory assessment: according to the criteria of TCVN 7030: 2002
LOCATION AND TIME PERIOD OF THE RESEARCH
- Location: Faculty of Biotechnology - Food Technology, Thai Nguyen University of Agriculture and Forestry
RESEARCH CONTENT
Content 1: Isolation of some strains of lactic acid bacteria that can be used in tofu production
Content 2: Selection of bacteria with good ferment ability for application in tofu production
RESEARCH METHODS
3.5.1 Content 1: Isolation of some strains of lactic acid bacteria that can be used in secondary production
3.5.1.1 Method of isolation and selection of lactic bacteria
To cultivate lactic acid bacteria from yogurt and fermented soy milk, a sample was mixed with 20 mL of solution and added to 100 mL of MRS broth medium The mixture was incubated at 37°C for 24 hours while being shaken at 150 rpm.
After diluting the incubation medium to a concentration of 10^-4, 100 µL was spread on MRS agar plates and incubated at 37°C After 48 hours, characteristic colonies were observed and selected for repeated inoculation on MRS agar until homogeneous colonies were achieved.
3.5.1.2 Determination of morphological, physiological and biochemical features
- Characteristics of colony morphology and bacterial cells: The isolated colonies were examined for cell morphology under the microscope on the oil objective lens X100
- Morphological, physiological and biochemical characteristics: Check some characteristics of lactic acid bacteria
3.5.2 Content 2: Selection of bacteria with good ferment ability for application in tofu production
3.5.2.1 Experimental set up test for soy milk fermentation
Prequalified strains of lactic acid bacteria were incubated to increase the biomass in 10 ml of MRS broth for 24 hours at 37 ° C
Prepare the soy milk solution (soybeans: distilled water = 1: 2.5) Pour into each glass jar 50 mL milk solution Afterward, add 5 ml of lactic bacteria strains and incubate at 41°C for 6-7 hours
The treatments were performed 3 times
3.3.5.2 Tofu production efficiency using lactic bacteria
The optimal pH for precipitating soy milk protein was established through prior experiments Following this, a strain with rapid fermentation capabilities and favorable sensory evaluations for soy milk fermentation was selected Tofu production was then carried out, and samples were taken to assess production efficiency, with the experimental setup detailed below.
Figure 3.1 Tofu production process using lactic acid bacteria
1 Indicate the quantity of total aerobic bacteria
The study aimed to evaluate hygiene levels in tofu processing and storage while also assessing the antibacterial properties of tofu made with lactic acid bacteria Two parallel samples were analyzed: one produced using lactic acid bacteria and the other made with plaster.
The method of enumeration of total aerobic bacteria is specified according to TCVN 5165 - 90 (Appendix 4)
Percentage of fermented soy milk used = 20%
Figure 3.2 Process of enumeration of total aerobic bacteria
Coliforms are a diverse group of Gram-negative, non-spore-forming bacteria that can ferment lactose, producing gas within 48 hours under suitable culture conditions This group includes various species such as E coli, Citrobacter, Klebsiella, and Enterobacter, and can thrive in both aerobic and anaerobic environments.
The purpose of this study is to evaluate the hygienic quality of water and the sanitary conditions in food processing, specifically by assessing fecal contamination in water sources It involves monitoring the fluctuations of two bacterial groups throughout production and storage, alongside other microbiological indicators The experiments were conducted using two tofu samples, with enumeration methods for Coliforms and Fecal Coliforms following TCVN 4882: 2007 (Appendix 5).
From the above dilutions, transfer 100 μl of sample to a Petri dish containing TGA medium (2 dishes each)
Count the colonies growing on the plate
Result: Total number of aerobic bacteria in the sample (CFU / g)
Prepare sample: 1g of tofu + 9ml of distilled water
Figure 3.3 Process of enumeration of Coliform
3 Indicate the quantity of total mold
Principle: Culture media containing inhibitors of bacteria (antibiotics such as Oxytetracylin or Chloramphenicol) are cultured at 30 ± 10C under aerobic conditions after 48 - 72 hours (Appendix 6)
Figure 3.4 Process of enumeration of mold 3.5.3 Sensory evaluation (Sensory evaluation by the method of scoring TCVN
For tofu, to assess the sensory quality, the assessment was conducted through the following four criteria: smell, taste, state, and color
The sensory evaluation of products adheres to Vietnamese standards (TCVN 3215 - 79), utilizing a scoring scale of 0 to 5 across six levels, where 5 represents the highest score and 0 the lowest Each inspector's evaluation is based on documented results, ensuring a consistent assessment process.
From the above dilutions, transfer 100 μl of sample to a Petri dish containing YGC medium (2 dishes each)
Count the colonies growing on the plate
The total count of aerobic bacteria in the sample is expressed in CFU/g To prepare the sample, combine 1g of tofu with 9ml of distilled water After conducting the analysis, compare the results with established descriptions and criteria, assigning an integer score based on the findings.
When evaluating a product with an odd number of testers (N), the average score is calculated as the mean of all testers' scores, rounded to two decimal places The weighted average point for each indicator is determined by multiplying the average score of that criterion by its corresponding importance coefficient.
Common point is the total weighted scores of all sensory parameters The six rating ranks are equivalent to the description content Vietnamese standard 3215 -
79 specifies the quality grades for products that have common points and weightless points for some corresponding criteria
Table 3.4 Quality level specified standards
Requirement about average score (without important coefficient)
Excellent 18.6 ÷ 20 Important criteria have higher than 4.7 score Good 15.2 ÷ 18.5 Important criteria have higher than 3.8 score Fairly good 11.2 ÷ 15.1 Each criteria have higher than 2.8 score
Bad 7.2 ÷ 11.1 Each criteria have higher than 1.8 score Very bad 4.0 ÷ 7.1 Each criteria have higher than 1.0 score
To meet the quality requirements (medium grade), the average score without important coefficient for each sensory criteria is 2.8 and the average score is at least 11.2 for each product
Color 5 Ivory white crust, milky white cut, uniform color, without any strange color spots on the bean, water escapes clear, when frying is even yellow
4 The crust and inside coat are ivory-white, uniform color, without any strange spots on the surface of the bean, the water escapes clear, when frying is even yellow
The crust and inner coating of the beans exhibit a consistent opaque yellow hue, free from any unusual spots on their surface When cooked, the water released appears slightly cloudy, and the frying process yields an even yellow color.
The crust should be either ivory white or opaque yellow, free from any unusual color spots When frying, the water may appear slightly opaque and yellow, indicating uneven cooking, with certain areas showing lighter colors.
1 The crust color is not uniform, the surface is a bit glossy, due to the viscous layer coming out, slightly opaque water escapes
0 The crust is black, white, speckled with pink color due to the development of mold, the water coming out have the color of rice water
Odor 5 The characteristic aroma of cooked soybeans, without any burning, sour, or any strange smell
4 The smell of beans fades, appears a burning odor, no smell of sour, strange smell
3 Clear burning smell, no sour odor
2 Clear burning smell, slightly sour
1 Clear burning smell, much sour
Taste 5 Typical taste of cooked soybeans , with no sour, acrid taste and have aftertaste
4 Typical taste of cooked soybeans , with no sour, acrid taste and have no aftertaste
3 Typical taste of cooked soybeans , a bit sour and acrid taste
2 Typical taste of cooked soybeans , have sour and acrid taste
1 Sour and acrid taste, no more typical taste of cooked soybeans
The flavor profile is extremely sour and acrid, lacking the typical taste associated with cooked soybeans The texture features a smooth crust with no cracks, allowing for clean cuts and a soft mouthfeel When pressed lightly, the product exhibits elasticity and a slightly rough surface, maintaining its integrity without breaking during frying.
4 Smooth crust, no cracks, smooth cuts, a little tough when eating, when pressing lightly by hands show elasticity, slightly rough, not broken when frying
3 Smooth crust, no cracks, smooth cuts, a little tough when eating, when pressing lightly by hands show no elasticity, slightly rough, not broken when frying
2 Smooth crust, no cracks, cuts are no longer smooth, hard to eat, broken when frying
1 The surface is not smooth, the cuts are not smooth, the structure is broken when frying
0 Too hard or too soft, the structure is broken when frying
Sensory evaluation was performed three times, with each session involving the preparation of two distinct tofu samples produced at three different times The sensory panel assessed these samples using a sensory description scorecard, with each member independently evaluating and documenting their results in the sensory assessment.
ANALYSIS METHOD
- Determine the pH index with a pH meter according to TCVN 6492: 1999
- Method of sensory assessment: according to the criteria of TCVN 7030: 2002
DATA PROCESSING METHODS
AND DISCUSSION
Results of isolation and selection of lactic acid bacteria
The results were isolated 11 strains of bacteria from 1 sample of yogurt and
1 sample of sour water (acidic water) Specifically, the bacteria strains are denoted as follows:
- Yogurt samples isolated 6 bacteria strains (symbols: SC1, SC2, SC3, SC4, SC5, SC6)
- Acidic water samples isolated 5 bacteria strains (symbols: DP1, DP2, DP3, DP4, DP5)
4.1.1 Biological characteristics of lactic acid bacteria isolated
4.1.1.1 Morphological characteristics of colonies and bacterial cells
Through the isolation process, I conduct to select the colonies with round shape, opaque white color, ivory surface and smooth edges
Figure 4.1 Colony on MRS agar
The bacterial isolates are primarily rod-shaped and can be categorized into two forms: short rod chains and long rods A representative image of some isolated cells is provided in the article.
Figure 4.2 and 4.3 Representative characteristic of bacteria cell
Some of the characteristics biochemical tests to determine the physiological and biochemical properties of lactic acid bacteria include:
- Gram staining: All strains isolated were stained Gram, in which 5/12 strains caught the purple color of the dye, indicating that these strains belonged to gram- positive bacteria
SC1 Pink color DP1 Purple color
SC2 Pink color DP2 Pink color
SC3 Pink color DP3 Purple color
SC4 Purple color DP4 Pink color
SC5 Pink color DP5 Pink color
Figure 4.4 Gram possitive bacteria Figure 4.5 Gram negative bacteria
Four strains of gram-positive bacteria were tested for catalase activity using 30% hydrogen peroxide (H2O2) The results indicated that none of these strains exhibited bubble formation, confirming the absence of catalase activity.
Figure 4.6 and Figure 4.7 Negative catalase
Base on physiological and biochemical characteristics of these 4 strains of bacteria, it can be concluding that they belong to the Lactobacillus Sp Family.
Experimental set up test for soy milk fermentation
After 8 hours of incubation, the pH is shown in Table
Table 4.2 pH of fermented soy milk of 4 bacteria strains after 8h
4.2.2 Sensory quality of fermented soy milk
The pH value table indicates that SC4 thrives in soy milk, effectively lowering the pH Alongside the rapid pH decrease, it is crucial to select a strain that maintains desirable sensory qualities during fermentation to ensure the final tofu product remains high-quality.
The sensory quality of lactic fermented soy milk is shown in Table 3.3
Table 4.3 Results of sensory evaluation of lactic fermented soy milk
SC4 Unpleasant smell, acrid sour
Bright yellow solution floating on top
The soymilk strongly precipitates on the bottom, smooth and without effervescence
DP1 Softened fermented flavor Milky white color The soymilk slightly precipitated on the bottom
Bright yellow solution floating on top, layer classification
The soymilk strongly precipitates on the bottom, smooth and without effervescence
Precipitated soymilk, with a suspension layer
Lactic acid bacteria SC4 demonstrated the ability to grow on soy milk medium, effectively lowering the pH within a short period However, sensory evaluations of soy milk fermentation using this strain revealed no positive outcomes.
DP3 is the one which got the finest sensory evaluation, and fermentation is only inferior to strains SC4 In overall, this strain has better ability among all
The selection of the DP3 strain was confirmed through initial results, demonstrating that it meets the research's initial criteria The subsequent phase involves examining the efficiency of tofu production utilizing this selected strain.
4.2.3 Carbohydrate metabolism of selected strain
The carbohydrate metabolism is shown in the table below
Table 4.4 Sugar fermentation test result of DP3
The DP3 strain is a Gram-positive, non-spore forming bacterium that typically lowers pH through fermentation and exhibits catalase activity When tested with three types of sugar, the DP3 strain produced a yellow fluid without gas bubbles, indicating that it ferments sugar to produce acid but does not generate gas.
Using the Bergey’s Manual of Determinative Bacteriology, it can be concluded DP3 strain belongs to the Lactobacillus genus It can either be
Lactobacillus casei or Lactobacillus delbroeckii
Tofu production efficiency
The process of producing tofu with lactic fermented soy milk tested is
Tofu production involves using 200g of soybeans and a fermented milk solution, following the process outlined in Figure 3.1 After pressing the tofu block, it is submerged in cold water to stabilize the product and prevent rapid souring, resulting in a total product weight of 400g.
Characteristics of freshly made LAB tofu
- Condition: The shell is smooth, without cracks, smooth cuts, soft
- Color: Ivory white crust, milky white cut, uniform color, absent no strange color spots on the tofu piece
- Flavor: typical aroma of cooked soybeans, with no sour odor, or any other strange odor
Determine the storage time
To determine shelf life products, we are using tofu sample and control sample to conduct storage The storage process are combined cooling condition and packaging
4.4.1 Indicate quantification of total aerobic bacteria
The results of determining the total number of aerobic microorganisms are shown in the chart Figure 4.8 and Appendix Table 8
Figure 4.8 Total Number of aerobic microorganism in 2 types of tofu
Figure 4.8 illustrates a notable difference in total aerobic microorganism counts between the two tofu samples As storage time progresses, the total aerobic microorganisms in both samples increase; however, the experimental sample shows a slower growth rate compared to the control sample, which reaches 3.1 x 10³ CFU/g after 9 days of storage.
Fermented soy milk, enriched with bacteriocin from laboratory bacteria, serves as an effective soy protein precipitation agent The presence of bacteriocin in the soy milk product partially inhibits the growth of aerobic microorganisms, enhancing its preservation and safety.
The results of determining the total number of Coliforms are shown in the chart Figure 4.9 and Appendix Table 9
Figure 4.9 Total number of coliforms in 2 types of tofu
The study revealed the presence of Coliform microorganisms, indicating contamination, with an observed increase in their numbers over time Notably, the control sample exhibited a faster growth rate of Coliforms compared to the other samples However, in the lactic fermented soy milk samples, the antibacterial compounds effectively inhibited the growth of these microorganisms.
The results of determining the total number of mold are shown in the chart Figure 4.10 and Appendix Table 10
Figure 4.10 Total number of mold in 2 types of tofu
DAY 0 DAY 3 DAY 6 DAY 9 DAY 12
DAY 0 DAY 3 DAY 6 DAY 9 DAY 12
Figure 4.10 illustrates a significant difference in total mold counts between two tofu samples Tofu made from lactic fermented soy milk showed no mold presence, while the control sample exhibited mold growth starting on day 6, with a sharp increase thereafter These findings indicate that the active compounds in fermented sour juices from DP3 strains possess strong antifungal properties.
4.4.4 Results comparing sensory quality between common tofu and tofu produced with lactic fermented soy milk
The overall sensory evaluation results for both control tofu and tofu made from lactic fermented soy milk are presented in the accompanying table, while a statistical analysis comparing the mean scores for the sensory attributes can be found in the appendix.
Table 4.5 Sensory score results between normal tofu and lactic fermented soy milk
Sample 1 st 2 nd 3 rd Average score
The study revealed that both control tofu and lactic-fermented tofu achieved favorable sensory grades, with lactic-fermented tofu scoring 17.44, surpassing the 17.14 score of traditional tofu Consequently, tofu made through lactic fermentation demonstrated superior sensory qualities, indicating its satisfactory appeal.