EFFECT OF VARIOUS FACTORS ON THE PROCESS OF YOGURT PRODUCT SUPPLEMENTED WITH SOYMILK... Thesis title: Effect of various factors on the process of yogurt product supplemented with soymilk
INTRODUCTION
Posing the problem
Dairy products are often favored for their uncomplicated composition, elevated nutritional content, and medicinal properties Milk and fermented dairy products are integral to a traditional diet, offering ample nutrients and regulating diverse physiological functions (Puniya, 2016) The production of yogurt has experienced a growth rate of more than 4% from 1995 to 2019 Consequently, there has been a consistent rise in yogurt consumption over the previous decade Yogurt contains more significant quantities of protein, vitamin B2, vitamin B12, calcium, magnesium, potassium, and zinc than milk Yogurt offers further health advantages beyond simply providing nutrients due to its inclusion of distinctive bioactive components and living and active cultures (Cifelli et al., 2020)
According to (Connect, 2024), research published in Jan 2024, the global economy is recovering, and the growth of the yogurt industry in 2021 is expected to undergo substantial changes compared to the previous year Based on their most recent assessment, the worldwide Yogurt market is projected to reach a size of USD million in 2022, compared to USD 68720 million in 2021, representing a change of % between the two years, and reach USD 88830 million by 2028, with a compound annual growth rate (CAGR) of 3.7% throughout the forecast period
Amidst the recent epidemic, there has been a rise in consumer consciousness regarding the positive impact of consuming yogurt on one's health Hence, to cater to the demands of consumers, in addition to offering a wide range of tastes and packaging options, customers have had a significant focus on plant-based products due to dietary restrictions and vegetarianism Plant-based yogurts made from soy, almond, coconut, and oats have become popular among customers who want alternatives to dairy products ("Yogurt Market– Global Industry Size, Share, Trends, Opportunity, and Forecast, 2018- 2028," 2024)
Soymilk is devoid of lactose, rendering it an appropriate option for people with lactose intolerance Furthermore, it possesses a high content of protein and minerals This option is appropriate for plant-based yogurt products because of its low levels of
2 cholesterol and carbs (Odo, 2003) Using Bifidobacterium spp in the soymilk fermentation process can effectively mitigate the undesirable beany taste and the presence of oligosaccharides The distinctive taste of soymilk is due to the presence of volatile chemicals, including n-pentanal and n-hexanal, which occur naturally in soymilk The consumption of oligosaccharides, specifically stachyose and raffinose found in soymilk, can result in the production of CO2 and methane In turn, gut microorganisms can cause flatulence during the metabolic process of these oligosaccharides (Shah, 2017)
Soy yogurt is produced through the fermentation of soymilk using only L delbrueckii ssp bulgaricus Soy yogurt can be fortified by adding cow's milk or skim milk powder to soymilk, with a maximum concentration of 3% Adding these ingredients typically enhances the taste and creates a firm and smooth texture (Shah, 2017) Conducting research and determining the proportion of soy milk to cow's milk in creating soymilk-enriched yogurt is crucial The article (Šertović et al., 2019) examined the proportion of soy milk to whole milk in creating yogurt enriched with soy milk It fermented using a combination of yogurt culture strains, namely Lactobacillus (L bulgaricus) delbrueckii subsp bulgaricus, Streptococcus thermophilus (Str thermophilus), and Lactobacillus acidophilus Hence, we choose to undertake a research endeavor to examine the proportion of soy milk to reconstituted milk derived from skimmed milk powder, along with several other influential parameters.
Research objective
Determine the impact of adding soymilk to yogurt on the overall quality of the final product
Provide the technological parameters for the experimental production of set yogurt- added soymilk.
Research object and scope
• Skim milk powder from Fonterra™ Dairy for Life, imported by Dai Tan Viet Joint Stock Company (145 Ton That Dam str, Ben Nghe ward, District 1, Ho Chi Minh City)
• Soymilk processed from Xuan Hong soybean
• The starter bacterial mixture comprised of two strains of Lactobacillus (L bulgaricus) delbrueckii subsp bulgaricus, and Streptococcus thermophilus (Str thermophilus) of Hansen Company (Denmark) and imported by Brenntag Vietnam
Company, which is situated at 120 Hoang Hoa Tham Street, Ward 7, Binh Thanh
District, Ho Chi Minh City
• Sugar from TTC – Bien Hoa Join Stock Company
• Set yogurt samples with different ratios of added soy milk to reconstituted milk, sugar content, and incubation temperature
The research was conducted at the laboratory of the Food Technology Major, Faculty of Chemical and Food, Ho Chi Minh City University of Technology and Education, at a laboratory scale.
Research content
The project “Effect of various factors on the process of yogurt product supplemented with soy milk” includes the following content:
• Effect of soymilk concentrations on the qualities of set yogurt
• Study the effects of sucrose content and incubation temperature on the qualities of set yogurt and choose the optimum range for this study
• Evaluate the chemical composition (fat, protein) and microbial criteria of set yogurt supplemented with soymilk.
Scientific and practical values
The utilization of the production process of yogurt from skim milk powder combined with soymilk is a helpful point of reference for academic research and study at universities
The project's novelty is in the exclusive utilization of skim milk and the incorporation of soy milk to enhance the texture of yogurt products
The topic also contributes to processing soymilk addition yogurt, which can be a reference for various yogurts with other legume-based additions
The research findings of the subject yielded technological parameters for conducting experimental research on the manufacturing of yogurt using skim milk enriched with soymilk
The production technique of this product can be applied to small-scale or large- scale production, allowing for a wider variety of legume-based milk to be added to yogurt to improve its nutrition and texture.
Report layout
This graduation thesis comprises 5 chapter
• Chapter 3: Material and research methods
LITERATURE REVIEW
Overview about yogurt
Nourishment is an intricate chemical system, not simply a chemical provider Most commodities, such as pharmaceuticals, fuels, metals, glass, ceramics, textiles, and paper, are composed of one or a few chemicals However, natural foods typically contain several compounds, and their properties are often influenced by small rather than significant elements (Patrick & Therese, 2021) The primary purpose of foods is to provide sufficient and balanced levels of macro- and micronutrients However, this is particularly relevant for individuals in industrialized societies who tend to consume adequate or even excessive quantities of nutrients (Patrick & Therese, 2021)
The therapeutic properties of foods are achieved mainly by fermentation, which induces physicochemical alterations in the food matrix, resulting in increased nutritional value and improved health benefits (Shiby & Mishra, 2013) The term "fermentation" originated from the Latin word "fervere" and was subsequently described by Louis Pasteur as "life without air." This is a metabolic process that obtains energy from organic compounds without the assistance of any external factors (Shah, 2017) During fermentation, the introduced microorganisms release several beneficial metabolites and break down the complex components of food (such as carbs, proteins, and lipids) into simpler forms that are bioactive, easily digestible, and meet nutritional requirements (Shiby & Mishra, 2013)
Yogurt is a type of milk that has undergone fermentation using a combination of
"Streptococcus thermophilus" and "Lactobacillus delbrueckii ssp bulgaricus cultures" (Shah, 2017) These cultures utilize lactose fermentation in milk, producing lactic acid, which leads to the curdling and formation of yogurt It can be augmented with fruits to intensify the taste The beneficial properties of yogurt having living and active cultures are extensively demonstrated in enhancing health (Puniya, 2016)
In addition to the typical yogurt starter bacteria, S thermophilus (ST) and L delbrueckii ssp bulgaricus (LB), various other adjunct bacteria have been utilized in the manufacture of yogurt over the past few decades Additional often employed bacteria in yogurt manufacturing include Lactobacillus helveticus, Lactobacillus casei, Lactobacillus
6 jugurti, and various species of Bifidobacterium In Australia, yogurt can be made using ABT (Acidophilus, Bifidobacterium, and Thermophilus) starter culture This starter culture consists of the bacteria S thermophilus, Lactobacillus acidophilus, and Bifidobacterium spp., with S thermophilus being the primary fermenting bacterium in this group (Shah,
Figure 2 1 Various type of yogurt product
In the past, humans utilized fermentation as a means of preserving milk The origin of fermented milk products cannot be traced back due to the need for records However, it is believed that these items originated in the Middle East region, predating the Phoenician era The usage of traditional fermented milk beverages, such as laban rayeb and laban khad, in Egypt can be traced back to approximately 7000 BC (Shah, 2017)
The term "yogurt" is thought to have originated from the Turks in the 8th century, initially appearing as "yoghurut." Therefore, it is presumed that the Turkish nomads in Asia were the ones who produced yogurt The invasion of Mongols, Tartars, and other Asian kings to Russia and Europe is thought to have been disseminating yogurt and fermented milk to other regions globally (Shah, 2017)
Yogurt has gained significant popularity and is now a staple in the diets of people in Europe, Australia, and various other regions worldwide Commercial yogurt and fermented milk production is now widespread in most significant nations Many localities still adhere to traditional methods of yogurt manufacture for everyday consumption (Shah, 2017)
Yogurt can be categorized into two groups: regular culture yogurt and bio- or probiotic yogurt Conventional yogurt is produced through the action of L delbrueckii ssp bulgaricus and S thermophilus bacteria These bacteria can enhance the beneficial microorganisms found in yogurt, which contribute to the overall health of the digestive system On the other hand, bio-yogurts are made with specific strains of bifidobacteria and
L acidophilus, which offer various health advantages Bio-yogurt is highly favored due to its mild, creamy taste and lower acidity It enhanced digestion and fostered optimal health
In addition to this categorization, the yogurt products offered in the market come in diverse flavors, textures, and forms that cater to a wide range of tastes and meal times These can be ingested as either a light meal, a sweet treat, or a component of a larger dish Yogurt can be classified based on its physical and chemical properties and the range of tastes added to it (Banerjee et al., 2017)
• BASED ON THE CHEMICAL COMPOSITION OF THE PRODUCT
Yogurt can be classified into three categories based on its fat level The first type is low-fat yogurt, created from partially skimmed milk The second type is non-fat yogurt, manufactured from fully skimmed milk The third type is standard yogurt, generated from full-fat milk (Banerjee et al., 2017)
• BASED ON THE PHYSICAL NATURE OF THE PRODUCT
Yogurt can be categorized as solid, semi-solid, or fluid based on physical properties Yogurts that have a firm consistency undergo incubation and are cooled while still in their final packing Stirred yogurt and fluid or drinking yogurt, which has a semi-solid state and a fluid character, is made by incubating the mixture in a tank and then breaking it up by stirring before cooling and packaging (Banerjee et al., 2017)
• BASED ON THE FLAVOR OF THE PRODUCT
Incorporating different flavors would satisfy the consumer's preferences and result in a diverse range of items Flavors can be included either prior to or after the homogenization process Yogurts can be classified into three categories: plain yogurt, fruit yogurt, and flavored yogurt, depending on the specific taste that is added to them Yogurt is offered in various tastes, including apple, apricot, black cherry, black currant, blueberry, lemon, mandarin, raspberry, strawberry, peach,
8 cereal, vegetables, chocolate, vanilla, caramel, and ginger Typically, flavors are incorporated into yogurt during the production process to augment the variety of tastes and intensify the sweetness of the yogurt (Banerjee et al., 2017)
Dairy products serve as a solid basis for the creation of health-enhancing components that can be used in the production of functional foods and dietary supplements Fermented foods provide strong detoxifying properties, enabling them to extract various heavy metals from the body In addition, fermented foods that are enhanced with probiotics include a wealth of vital nutrients such as vitamins B12, B6, K2, biotin, protein, essential amino acids, and fatty acids that satisfy the body's requirements (Puniya, 2016)
Raw material
Mammals produce milk to provide food to their offspring However, for numerous generations, it has also been a significant component of the human diet for infants and as a regular part of daily nutrition in many communities Since ancient times, humans have consumed milk obtained from domesticated animals as a source of nourishment (Matalas et al., 2001)
Milk contains essential bioactive components such as energy, water, carbohydrates, fats, proteins, vitamins, minerals, and minor biological proteins and enzymes These components contribute to the nutritional value of milk, making it a nutritious and complete food With a water content of around 87%, it serves as a valuable dietary source of hydration Carbohydrates, specifically lactose, glucose, and galactose, are the main energy source in milk Milk is a source of essential fatty acids, including linoleic and linolenic acids, which cannot be naturally generated by the body and must be obtained from fermentation or dietary supplementation It contains substantial casein and whey proteins (Puniya, 2016)
Milk provides all the body's essential amino acids, including vitamins A, D, E, K, riboflavin, niacin, pantothenic acid, and folate Milk contains many minerals, such as calcium, copper, iron, manganese, magnesium, phosphorus, sodium, and zinc, which play distinct roles in the body, including enzyme functioning, bone building, water balance management, and oxygen delivery Additional proteins and enzymes in milk that are nutritionally significant include lactoferrin and lactoperoxidase (Puniya, 2016)
Table 2 1 Chemical Composition of Milk of the Main Milk-Producing Animal
Highly perishable milk can be stored for future use by eliminating water through drying techniques such as spray drying and roller drying This process prevents the growth of bacteria and inhibits enzymatic processes In addition, milk powders are commonly utilized for their simplicity in transportation, handling, processing, and product compositions However, they are vulnerable to various alterations, including moisture absorption, softening, browning, compaction, collapse, or caking (Pugliese et al., 2017)
Skimmed milk, also known as skim milk, is produced by completely separating the cream, often called milk fat, from whole milk Occasionally, a portion equivalent to half of the cream is extracted, producing semi-skimmed milk Skim milk powder (SMP) and other dehydrated dairy components should ideally possess a pristine, sugary, and agreeable flavor devoid of taste imperfections (O'Sullivan, 2017) The FDA regulation mandates a minimum content of 8.25% non-fat milk solids Nevertheless, the yogurt industry utilizes a maximum of 12% Solids-Not-Fat (SNF) in the yogurt mixture to produce a dense and creamy texture resembling custard The milk fat levels are regulated to conform to a standard The milk fat level in a non-fat yogurt mix does not exceed 0.5% (Chandan, 2014)
Stabilizer Concentration in Yogurt Mix
Pectin (low methoxy for yogurt) 0.08 - 0.20
Pectin (high methoxy for yogurt beverages) 0.30 - 0.50
Table 2 2 Stabilizers and their concentrations for use in yogurt and yogurt drinks (Shah, 2017)
Stabilizers are hydrocolloids derived from plants and animals The primary objective of including stabilizers in yogurt is to enhance its texture and increase its thickness while reducing the separation of whey and retaining the gel-like structure even after undergoing processes such as pumping, mixing, and cooling The stabilizer enhances the longevity of the product and ensures a satisfactory level of consistency across several
14 batches Stabilizers create gel structures in water, reducing the amount of free water available for syneresis Furthermore, specific stabilizers form complexes with casein, resulting in increased viscosity and enhanced defense against syneresis (Shah, 2017)
The discovery of xanthan gum dates back to the 1960s, and it was subsequently introduced into commercial use throughout the 1970s Xanthan is a microbial polysaccharide that is released by the bacterium Xanthomonas campestris It is manufactured in large quantities through aerobic fermentation for use in the food and pharmaceutical sectors Xanthan exhibits elevated viscosity even at low concentrations, rendering it an exceptional food addition for syrup, stabilizing, and thickening Xanthan is a stabilizer in most liquid and semiliquid foods and imparts structural integrity to many dairy products The FDA has approved Xanthan for many years as a permissible ingredient, and it has been extensively utilized in the food sector (Nasrollahzadeh et al., 2021)
Figure 2 3 Xanthan Gum 2.2.4 Soy bean
The soybean, scientifically known as Glycine max (L.) Merrill is an ancient crop from China and among the Far East's oldest cultivated plants The Chinese and other Oriental cultures, such as the Japanese, Korean, and Southeast Asians, have relied on beans in different forms for ages as a significant source of nutritional protein and oil Due to its enormous protein yield per unit of land, soybeans have earned several names such as
"yellow jewel," "great treasure," "nature's miracle protein," and "meat of the field." Some
15 people view this bean as a potential solution to global hunger and a promising source of future protein Recently, the soybean has been acclaimed as a potential tool in combating chronic illnesses (Liu, 2012)
Due to its distinctive chemical composition, the soybean is highly regarded as an economically valuable agricultural commodity Compared to other legume species and cereals, it has the highest protein level, approximately 40% Other legumes typically have a protein content ranging from 20% to 30%, while cereals have a protein content ranging from 8% to 15% The soybean contains approximately 20% oil, the second-highest oil content among all edible legumes Soybeans also include phospholipids, vitamins, and minerals, which are all valuable components In addition, soybeans contain numerous bioactive minor compounds, including trypsin inhibitors, phytates, and oligosaccharides Additional compounds, such as isoflavones, are currently becoming acknowledged for their potent capacity to inhibit human malignancies and other ailments (Liu, 2012)
Soy protein is a significant constituent of the diet of animals raised for food and is becoming more crucial in the human diet Nevertheless, soy protein is suboptimal as a protein source due to its inadequate supply of the essential amino acid methionine Supplementing soy newborn formulae with methionine is advantageous, but it has little effect on meals meant for adults who already have sufficient nitrogen consumption Soy protein has a more significant lysine level than wheat proteins, although it is still lower than the lysine content of milk protein casein (Friedman & Brandon, 2001).
Soymilk
The Chinese highly favor soymilk, while its popularity is relatively lower among the Japanese and Western cultures The health advantage of soy protein in lowering cholesterol levels, which is associated with heart disease, has led to a rise in the sales of soymilk and the usage of soy in food products This growth is attributed to the US FDA now permitting a health claim to be made if a food item has a minimum of 6.25 g of soy protein and low cholesterol levels, saturated fat, and total fat (Snyder & Wilson, 2003)
The conventional method of making soymilk involves soaking soybeans overnight and grinding them with extra water The resultant mixture is heated and agitated for 1-30 minutes, which may vary depending on the temperature The milk's heating process
16 enhances its nutritional quality by deactivating trypsin inhibitors and enhancing its taste by deactivating lipoxygenase and evaporating certain undesirable flavor chemicals produced during the grinding process Applying heat to the milk also enhances its longevity by decreasing the number of microorganisms present Next, the hot mixture is passed through a fabric or synthetic bag to isolate the insoluble fiber residue from the soymilk If desired, the resulting soymilk can be flavored Additionally, it is possible for the product to undergo processes such as pasteurization, homogenization, or sterilization prior to being bottled, aseptically packaged, or retorted (Snyder & Wilson, 2003)
For manufacturing soymilk, it is generally desirable to use soybeans with a high protein content, a clear or yellow hilum, and large seeds Approximately 200 grams of soybeans will produce approximately 1 liter of soymilk To enhance the shelf life of soymilk, it can undergo spray-drying or roller-drying processes to transform it into a dry powder, similar to the method used for cow's milk After spray-drying, instant soymilk can be used in beverages, confections, and meat fillers (Snyder & Wilson, 2003)
Figure 2 4 Variety of Soymilk Products 2.2.2 Classification of Soymilk
Due to technological advancements and customer demands, there are currently two main categories of Soymilk: Traditional Soymilk and Modern-style Soymilk.(Odo, 2003)
• Traditional (Chinese-style) Soymilk (Regular Soymilk)
Regular soymilk possesses a mild, bean-like taste and is deemed satisfactory by the Chinese population This soymilk can be used to produce tofu curd This soymilk is utilized for culinary purposes in North-East Asia and serves as a customary morning beverage in South-East Asia
• Modern-style Soymilk (Reconstituted Soymilk)
Two distinct categories of reconstituted soymilk exist It possesses a subtle taste reminiscent of beans and is made by blending soaked soybeans with hot water Individuals who frequently consume soy products have a preference for the subtle taste resembling that of beans found in soymilk The legume-like taste is a significant determinant Flavors are frequently used (to conceal) in order to diminish the bean-like taste in soymilk North-East Asians consume this variety of soymilk Another variant of reconstituted soymilk is the Western-style soymilk, which is distinguished by a taste not reminiscent of beans This form of soymilk is made using contemporary techniques developed by Cornell University, the United States Department of Agriculture (USDA), and the University of Illinois This particular soymilk variety possesses a taste that closely resembles that of dairy products and is frequently subjected to ultra-pasteurization The product is packaged in aseptic Tetra Brik packs or retort standing pouches and is delivered and sold without requiring refrigeration This variety of soymilk is gaining significant popularity in North America and Europe
Table 2 3 Compositions of soymilk, bovine milk, and human milk (Odo, 2003)
Table 2.3 lists the compositions of traditional soymilk, bovine, and human milk compositions Soymilk has a slightly higher protein composition compared to bovine and human milk However, its fat and carbohydrate levels are 30% lower, resulting in 30% fewer calories per 100 g Regarding nutrients, the calcium level in soymilk is 50% less than that in human milk, while the potassium level is twice as high Soymilk has an iron level 12 times more than bovine and human milk, making it a potent treatment for anemia (Odo, 2003)
Soymilk includes small quantities of fat-soluble vitamins (A, D, and E), but slightly lower levels of B-group vitamins (B1, B2, niacin) than other milk varieties
Soymilk has lower saturated fat and cholesterol levels than cow's milk and human milk Health experts advise limiting the intake of saturated fat and cholesterol to lower the likelihood of developing heart disease
Soymilk is lactose-free, making it a suitable choice for individuals with lactose intolerance The popularity of it is currently on the rise in North America and Europe Asians exhibit a reduced occurrence of estrogen-related malignancies and a lower occurrence of climacteric syndrome and osteoporosis This phenomenon has been attributed to their significant consumption of soybean products rich in phytoestrogens, such as isoflavones
As mentioned above, soy milk contains a high concentration of isoflavones Isoflavones offer several health advantages, such as lowering cholesterol levels, alleviating menopause symptoms, preventing osteoporosis, and reducing the incidence of some cancers Isoflavones possess antioxidant properties that safeguard our cells and DNA from oxidation (Kant & Broadway, 2015)
Soy milk is abundant in omega-3 fatty acids, essential fats the human body cannot synthesize independently Omega-3 fatty acids are associated with a decreased likelihood of developing dementia and Alzheimer's disease Soy milk can also contribute to the maintenance of the human cardiovascular system Regardless of fortification, soy milk is a highly beneficial source of potassium Potassium is crucial in regulating blood pressure and maintaining a steady heart rate Moreover, there is a correlation between soy milk
19 consumption and reduced cholesterol levels, particularly in individuals with elevated cholesterol.
Domestic and oversea research situation
Yogurt supplemented with soy milk is a relatively new product in the Vietnamese market While learning about the research works of the above product, our team found some previous studies—one of the research articles (Dương, 2009) The author surveyed how Brix and temperature affect product quality The results recorded Brix degrees 18, 19,
21, and temperatures 40, 42, and 44 o C are the best conditions for fermentation with the best product quality
Another study(Trần Thị Hà Ny, 2015) used Kefir microflora to add to soy milk to diversify the product and reduce the amounts of oligosaccharides in soy milk Sensory evaluation results show that soy yogurt is best fermented with milk produced with the ratio of 125g beans/ 600ml water, 6% (v/v) seed, within 28 hours, the additive ratio The thickener used is 0.2% Gellan gum (w/v) and 70% sugar solution at a ratio of 8% (v/v)
However, research articles on factors affecting yogurt supplemented with soymilk in Vietnam are still very new Therefore, our group decided to carry out the project “Effect of various factors on the process of yogurt product supplemented with soy milk”
Yogurt enriched with soy milk is a promising product, particularly as the demand for environmentally friendly lifestyles and plant-based products continues to rise This necessitates immediate research efforts to enhance the product's quality consistently Several studies have examined the impact of several factors on product quality, including the ratio of soy milk to milk, additives incorporated into the product, and the specific strains of microorganisms used for fermentation
In 2010, a study by (ESTÉVEZ et al., 2010) was carried out on the effect of two levels of solids and two sugar combinations on the quality of a soymilk yogurt-type food
As a result, Soymilk-based yogurt with 8% solids, enriched with mixtures of sugars like glucose/fructose or glucose/sucrose, had low astringency, mild acidity and aroma, and pleasing appearance, which made them the most accepted ones On the other hand, yogurt
20 with 11% solids had higher viscosities, lower syneresis, and higher Titratable acidity, but they developed a chalky texture
On the other hand, A study by (Šertović et al., 2019) analyzes the nutritional, physiological, microbiological, and sensory characteristics of probiotic beverages made from varying proportions of cow's milk and soy beverage (25:75, 50:50, and 75:25) In result, the primary sugar molecules underwent efficient conversion into lactic acid through the process of fermentation Mixing cow's milk with soy beverage dramatically increased the sensory qualities of the product, especially its fragrance, taste, and color The acceptability test demonstrated favorable reception among prospective consumers for all fermented beverage samples, except those derived primarily from soy beverages
However, there is limited data available on the impact of soymilk supplementation on the characteristics of soy yogurt products, particularly in Vietnam Given the conditions indicated above, our team decided to carry out the research “Effect of various factors on the process of yogurt product supplemented with soy milk”
The foundation of our study primarily relies on the research of (Šertović et al., 2019) We have also conducted additional experiments to enhance this research Our study is based on the same ratio of soy milk to milk as the reference but replaced with skim milk
In addition, we also investigated the effects of sugar content as well as incubation temperature
MATERIALS AND RESEARCH METHOD
Materials, chemicals, and equipment
This study used skim milk powder from Fonterra™ Dairy for Life, imported by Dai Tan Viet Joint Stock Company (145 Ton That Dam str, Ben Nghe ward, District 1, Ho Chi Minh City)
Xuan Hong soybean is selected to be our ingredient for the Soymilk solution Beans are soaked overnight (12 hours) in water before being processed into Soymilk
Figure 3 3 Flow Chart of Soymilk Processing
Soaking: Soybean soaking is a conventional method primarily employed to soften the grains and simplify their subsequent cooking The soybeans are immersed in water for a duration of 12 hours at an ambient temperature.(Lima et al., 2014)
Peeling: Remove the outer layer of the soaked bean
Blending: After being peeled, the beans will be mixed with water in a ratio of 1:8 using a blender The mixture will be blended until the desired smoothness is achieved(Zhang, 2012)
Filtering: After blending, the mixture will be filtered through a cloth to remove bean residue, creating a liquid mixture
Pasteurizing: The solution will be heated at 90 o C, maintained for 10 minutes
The starter bacterial mixture used in this study comprised of two strains of Lactobacillus (L bulgaricus) delbrueckii subsp bulgaricus, and Streptococcus thermophilus (Str thermophilus) These strains were obtained from CHR.Hansen Company (Denmark) and imported by Brenntag Vietnam Company, which is situated at 120 Hoang Hoa Tham Street, Ward 7, Binh Thanh District, Ho Chi Minh City
Figure 3 4 Hansen Company Starter Culture Sugar
The sugar used in this study is from TTC – Bien Hoa Joint Stock Company
Figure 3 5 Bien Hoa Join Stock Company Sugar
Xanthan gum used in this study was purchased at Hoa Nam chemical and laboratory equipment store located at 239/4 Ly Thuong Kiet str, Ward 15, District 11, HCMC
Sodium hydroxide (NaOH), Ethanol, Ammoniac (NH3), Petroleum ether (60-90), Diethyl Ether ((C2H5)2O), Hydrochloric acid (HCl), Sulfuric Acid (H2SO4), Phenolphthalein (C20H14O4), Sodium Chloride (NaCl), Potassium Sulfate (K2SO4), Copper Sulfate Pentahydrate (CuSO4.5H2O), Boric Acid (H3BO3)
• Rheology analyzer (Rheostress Drehkorper, Germany)
• Checker pH Tester (Hanna Instrument, Rumani)
• 2 and 4-digit analytical balance (Precisa, Switzerland)
• LAB Count Plate Petri-film (3M, USA)
• Texture Analyzer CT3 (Brookfield, USA)
Beaker, Erlenmeyer flask, test-tube, test-tube rack, double headed stainless spoon, micropipette 100-1000 àL, micropipette tips, pipette, burette, thermometer, dispensing bottle, volumetric flask, volumetric cylinder 50mL, 100mL, 500mL, glass rods, aluminum foil.
Research scheme and production of Yogurt subjoin Soymilk
Investigating the effects of factors during yogurt fermentation
Evaluate the quality of the product
Overview of ingredients Overview of analytical methods
Survey fermentation conditions according to variables with the objective function:
• Ratio of addition of nut milk during fermentation: 0:100, 25:75, 50:50, 75:25
• Sugar content ratio during fermentation: 0, 5, 10, 15 (10%)
• Fermentation temperature: 37 0 C, 40 0 C, 43 0 C, 46 0 C pH measurement, acid titration (3 times) Evaluate product structure: rheology, TPA (3 times) Count the content of lactic acid microorganisms Chemical composition of the product (protein, fat)
3.2.2 Production of Soy-added yogurt
Reconstruction Homogenization Mixing Pasteurization Cooling Inoculation Filling Incubation
Figure 3 7 Yogurt supplemented with Soymilk processing
Purpose: Combine the skim milk powder and water to get a reconstituted milk liquid with a consistent dry matter content of 11%
Proceed: Reconstituting 11.43g skim milk powder in 88.57ml of water at 43℃ to get 100g reconstituted milk with 11% dry matter
The weight of whole milk powder is calculated using a specific formula
Where a was the amount of skim milk powder (g); b was the dry matter content needed (%); c was the dry matter content in 100g milk powder material (g)
Purpose: Milk homogenization is a widely used technique in yogurt production as it prevents the separation of cream during fermentation and storage, enhances uniformity, boosts the whiteness, and minimizes the release of liquid in the product.(Trujillo et al., 2016) In order to achieve a homogenous mixture, Soymilk is also added in this phase
Proceed: Milk homogenization is a widely used technique in yogurt production It prevents the separation of cream during fermentation and storage, enhances uniformity, boosts whiteness, and minimizes liquid release in the product (Trujillo et al., 2016) Soy milk is also added in this phase to achieve a homogenous mixture
Purpose: Add the sugar to the solution
Proceed: The investigated ratio of sucrose was added to the milk mixture after homogenization and stirred using a sterilized spoon for approximately 5 minutes until the mixtures achieved perfect homogeneity
Purpose: Eliminate undesirable bacteria, particularly harmful ones; impede the activity of enzymes; alter the structure of whey proteins, enhancing the firmness of yogurt's gel
Proceed: The milk mixture underwent pasteurization at a temperature of 90℃ for a duration of 10 minutes.(Chandan & O'Rell, 2006)
Purpose: Reduce the temperature of the mixture to the suitable level in order to proceed with the inoculation procedure
Proceed The mixture is cooled at room temperature until it reaches 43 o C in a sterile condition
Purpose: Inoculate the starting yogurt culture into the milk mixture to initiate fermentation
Proceed: Under sterile conditions, bacterial isolates ( L delbrueckii ssp bulgaricus, S thermophilus) were inoculated into the milk mixture at a concentration of
0.015 % (w/w) at 43 o C Then, the mixture was stirred with a clean spoon for 5 min to dissolve the starter culture into the solution
Purpose: The mixture is poured into jars to start the incubation process
Proceed: After sterilization, the glass jar will serve the purpose of containing a
Purpose: Establish the proper temperature conditions for the fermentation process and maintain strict regulations
Proceed: Modify the temperature configuration of the thermostatic bath by the experimental design Once the desired temperature is reached, the yogurt jars will be placed inside, initiating the fermentation process The incubation process will terminate once the pH hits 4.6 (Lee & Lucey, 2010).
Experiment Design
3.3.1 Experiment 1: Effects of soy milk ratio with reconstituted skim milk on the qualities of set yogurt supplemented with soymilk
Purpose: Estimate the proper ratio of soymilk to be used in the manufacturing of yogurt that is enriched with soymilk
Fixed Factor: Dry matter in reconstituted milk was 11%, sugar content was 10% and incubation temperature was 43 o C
Procedure: The yogurt production process was executed according to the procedures outlined in Figure 3 Then, soymilk was incorporated into reconstituted milk in ratios of 0%, 25%, 50% and 75% w/w (Soymilk to reconstituted milk), corresponding to the coded samples in the acronym list: CY, SY_25, SY_50 and SY_75
Determined parameters: Physicochemical properties (pH, titratable acidity), chemical composition (fat, protein), rheological measurement, texture profile analysis, Fourier – Transform Infrared Spectroscopy, Scanning Electron Microscopy and LAB counting
3.3.2 Experiment 2: Effects of different sucrose content on the qualities of set yogurt
Purpose: Examine the impact of varying sugar concentrations on the overall quality of yogurt and ascertain the optimal quantity of sugar to be incorporated into yogurt
Fixed Factor: Dry matter in reconstituted milk was 11%, without addition of soymilk and incubation temperature was 43 o C
Procedure: The yogurt production process was carried out according to the procedures outlined in Figure 3 Sugar will be added to milk after homogenization at rates of 0%, 5%, 10%, 15%, corresponding to the coded samples in the acronym list: YS_0, YS_5, CY, YS_15
Determined parameters: Physicochemical properties (pH, titratable acidity), rheological measurement and LAB counting
3.3.3 Experiment 3: Effects of incubation temperature on the qualities of set yogurt
Purpose: Study the influence of incubation temperature on the quality of yogurt and ascertain the optimal temperature for the fermentation process in yogurt production
Fixed Factor: Dry matter in reconstituted milk was 11%, without addition of soymilk and sugar concentration was 10%
Procedure: The yogurt production process was handling according to the procedures outlined in Figure 3 Temperature surveys was performed at the incubation step
31 with the following temperatures: 37 o C, 40 o C, 43oC, 46 o C corresponding to the coded samples in the acronym list: TY_37, TY_40, CY, TY_46
Determined parameters: Physicochemical properties (pH, titratable acidity), rheological measurement, and LAB counting
3.4.1 Method for determining chemical composition
The fat content of yogurt samples was determined by Adam Rose–Gottlieb
The protein content of yogurt samples was determined according to the Kjeldahl method
The pH and titratable acidity of yogurt samples were analyzed using the methods specified in TCVN 6509:2013 and ISO 11869:2012
Principle: Ion exchange occurs between the sample solution and the inner solution of the glass electrode in accordance with the operation principle of a pH meter The pH meter measures the acidity or alkalinity of the solution by exchanging information across the glass membrane
Procedure: Calibrate the pH meter using pH 7.0 and 4.0 buffers, following the instructions provided for the pH meter To determine the pH, precisely measure 10 grams of the test sample and place it in a beaker Then, add around 10 milliliters of pure water and mix the contents Subsequently, the pH meter electrode should be immersed in the sample suspension, and the outcome should be carefully documented
3.4.3 Determination of titratable acidity (Nielsen, 2003)
Principle: The titration acidity of yogurt refers to the volume, measured in milliliters, of a 0.1 N sodium hydroxide solution needed to neutralize 10 grams of the yogurt product
Procedure: Adjust the sample temperature to approximately 25°± 2°C and agitate the sample using either a spoon or a homogenizer to ensure thoroughly mixing of the layers, including the lower levels The acidity level is assessed by titration using a sodium hydroxide solution Mix 10 grams of yogurt sample with 20 milliliters of distilled water in
32 a beaker Then, add 3 to 4 drops of phenolphthalein indicator and perform a titration using a standard solution of 0.1N NaOH Perform a titration on the combination until it exhibits a slightly pink hue, and there is no loss of color Record the volume of NaOH solution used, rounding to the nearest 0.05 ml
𝑚 Where, V: the volume of 0.1N NaOH solution, (ml); m: the weight of sample, (g); I: titratable acidity, (°T)
The rheological properties of yogurt samples were analyzed using a Thermo Scientific HAAKE Rheometer with a P35 Ti L (ỉ = 35mm) and a 1 mm gap distance The measurements were conducted at a temperature of 25℃ to compare viscosities and assess the fluid's behavior The experimental approach was adapted from the one described by Ren et al (2017) Before being placed onto the bottom plate of the rheometer, the sample was allowed to reach a stable temperature of 25°C for one hour Position 2g samples onto a stainless plate to assess indicators such as shear stress, shear rate, and apparent viscosity during a shear rate scan ranging from 1 to 300s-1 for the first cycle and 300 to 1s-1 for the second cycle
The data were organized into shear rate and shear stress variables and then fitted to the Herschel-Bulkley model:
𝜎 = 𝐾(𝛾 𝑛 ) + 𝜎 0 Where: 𝜎 is the shear stress (Pa.s)
𝛾̇ is the shear rate (s -1 ) n is the flow behavior index
K is the consistency index (Pa.s)
This type is suitable for a wide range of fluid foods In Herschel-Bulkley fluids, the apparent viscosity is directly proportional to the shear rates when the value of 𝑛 is between
0 and 1, indicating shear thinning behavior However, when the value of 𝑛 is between 1 and
∞, the apparent viscosity behaves oppositely, indicating shear thickening behavior (Steffe, 1996)
3.4.5 Method for enumeration of Lactic Acid Bacteria (LAB)
The Lactic Acid Bacteria Count Plate was employed to identify the presence of L.bulgaricus as a starting culture in yogurt The LAB counting procedure is executed according to the provided instructions Successive dilutions were made in a NaCl solution (8.5 g/L) and applied to the LAB suspensions in yogurt sample suspensions The initial suspension (1 mL) was mixed with 9 mL of sterile saline to create a diluted solution The test materials were diluted in a series, and then 1mL portions of the appropriate dilutions were used to introduce microorganisms into the 3M Petrifilm Count Plates Following inoculation, Petrifilm LAB Count Plates were placed in an incubator and kept at 37°C for
48 hours Plates with 15-300 colonies were gathered, and the colonies were counted and expressed as the logarithm of the number of colony-forming units per milliliter of yogurt sample (log CFU/mL) ("Petrifilm, M.," 2017)
The Texture Profile Analysis (TPA) was conducted with Brookfield's CT3 instrument equipped with a TA11/1000 Cylinder probe, which had a diameter of 25.4 mm and a length of 20 mm (Nguyen et al., 2017) This particular test was carried out using a prior report with a few alterations The samples were retrieved from a refrigerator set at a temperature of 4℃ and left at room temperature for approximately 1 hour before analysis The apparatus features a plastic cylinder that rotates at a constant velocity of 1 mm/s in both the upward and downward directions The plastic cylinder was inserted 10mm into the sample's surface and placed on a stationary table (TA - BT - KIT) The gel's hardness, determined by the force needed to compress and deform it, is directly linked to its structure and strength, making it a reliable indicator
Figure 3 9 Texture Analyzer CT3 3.4.7 Fourier – Transform Infrared Spectroscopy (FT-IR)
The FTIR analysis method utilizes infrared light to scan and analyze the chemical properties of test samples The soy yogurt underwent Fourier transform infrared (FT-IR) spectroscopy examination, using previously published instructions(Molaee Parvarei et al., 2021) Concisely, each sample weighing 1 mg was used for analysis The IR spectra were obtained using a NIR/MIR Frontier of PelkinElmer, within the frequency range of 4000-
The yogurt's microstructure was analyzed to assess the disparity in the composition between yogurts with and without added okra polysaccharide SEM sample preparation is conducted by RESEARCH LABORATORIES OF SAIGON HI-TECH PARK located at Lot I3, N2 Road, Hi-Tech Park, District 9, HCMC The samples were freeze-dried at the temperature < -50 o C in 8hrs In the next 8hrs, the samples were convectional dried at
100 o C Then, the samples were cut into 1x1cm, cover with Pt in 30mA for 30s Finally using FE-SEM scanning electron microscope to analyze and evaluate the surface
RESULTS AND DISCUSSION
Chemical composition of samples
The chemical compositions of soymilk, CY, SY_25, SY_50, and SY_75 was identified, including protein and lipid The results are displayed in Table 4.1
Table 4 1 Chemical composition of samples
Soymilk CY SY_25 SY_50 SY_75
According to analytical data (Table 4.1), soymilk's chemical composition includes 2.21% protein and 0.97% lipid However, the control yogurt has a fat content of 0.5% and a protein content of 3.39%
SY_25 is composed of 0.63% fat and 2.77% protein The protein and fat content of SY_50 was 2.73% and 0.77%, respectively The yogurt sample with 75% soy milk (SY_75) has 0.8% fat and 2.64% protein.
Effects of soymilk ratio on the qualities of set yogurt supplemented with soymilk
4.2.1 Changes of pH and titratable acidity of set yogurt supplemented with soymilk
Figure 4.1 shows the changes of pH of yogurt samples supplemented with different soymilk content
Figure 4 1 Changes of pH of set yogurt supplemented with soymilk during fermentation
The pH of yogurt samples made with different ratios of soy milk to reconstituted milk was monitored every 40 minutes during a 3.5-hour fermentation period at 43°C Yogurt made with only reconstituted milk (100% reconstituted milk) showed a slow initial decrease in pH However, yogurts with higher ratios of soy milk to milk generally had a faster drop in pH (Heydari et al., 2011) This means that the yogurt made with only milk took longer to ferment than the yogurts made with soy milk, even though they all fermented for the same amount of time The addition of soy milk to the reconstituted milk increases the rate of the fermentation process, as evidenced by the quicker pH drop Figure 4.1 reveals that reconstituted milk and soymilk blends achieved near-identical pH values to the control sample after exceeding 3 hours of incubation, although practically no coagulation was observed for samples to which soymilk was added at a shorter time with an increase in soymilk percentage As Figure 4.1 shows, this might be a result of the increase in total solids in mixtures (Riaz, 2005)and (Švejstil et al., 2015) have also reported Numerous soluble oligosaccharides, such as sucrose, raffinose, and stachyose, are found in soymilk These sugars are broken down by various lactic acid bacteria, which use them as fuel to create a variety of fermented dairy products (Hassanzadeh-Rostami et al., 2015) Additionally, the variation in the isoelectric point (PI) between soy milk and reconstituted milk may be the cause of the coagulation rate of samples obtained from
39 mixing the two types of milk (Hsia et al., 2016) Our results are consistent with those (Šertović et al., 2019)
Figures 4.2 shows the changes of titratable acidity of yogurt samples supplemented with different soymilk content
Figure 4 2 Changes of titratable acidity ( o T) of set yogurt supplemented with soy milk during fermentation
The titratable acidity of yogurt samples added 75% soymilk (SY_75) was highest with 99.06 o T and lowest was CY with 87.87 o T during 260 minutes of fermentation The addition of soy beverage to cow's milk resulted in an increase in the rate of pH drop during fermentation and increase in acidity The higher survival rate of L delbrueckii ssp bulgaricus in soymilk may be due to the existence of oligosaccharides in soymilk which help the growth of lactic acid bacteria (De Valdez & De Giori, 1993)
Herschel-Bulkley is one of the most often utilized models for predicting yogurt behavior This session will examine the correlation between shear rate (γ̇, 1/s) and shear stress (σ, Pa), as well as the link between shear rate (γ̇, 1/s) and apparent viscosity (η, Pa.s) of yogurt samples
The change in shear stress (σ, Pa) with shear rate (γ̇, 1/s) of soy yogurt samples was illustrated in Figure 4.3 and the regression equations presented the relationships between
Titra ta b le acid ity ( o T)
40 them at 1 st cycle (shear rate increased from 1 to 300s -1 ) and 2 nd cycle (shear rate decreased from 300 to 1s -1 ) in Table 4.2
Figure 4 3 Changes of shear rate & shear stress of set yogurt with supplemented soymilk at 1st cycle (left) and 2nd cycle (right)
Sh ear stre ss (Pa)
Shear rate (1/s) SY_50 CY SY_25 SY_75
Sh ear stre ss (Pa)
Shear rate (1/s)SY_50 CY SY_25 SY_75
Table 4 2 Herschel – Bulkley model equations of yogurt samples supplemented with soymilk
The 1 st cycle The 2 nd cycle
Figure 4.3 shows the shear rate and shear stress of soy yogurt; a higher shear rate corresponds to a higher shear stress At every shear rate, sample CY (100% reconstituted milk from skim milk powder) had a greater shear stress than the other samples Shear stress (τ) was measured at 19.73 and 37.67 Pa at the 1 st cycle with the flow of SY_25 (25% soy milk and 75% reconstituted milk blend) at 1 s -1 and maximum shear rate of 44.87 s -1 , respectively At SY_50 (50% soy milk and 50% reconstituted milk blend), their values were 15.8 and 35.39 Pa, respectively These indicate that less stress is needed for the sample SY_75 at (75% soy milk and 25% reconstituted milk blend) to flow This is corroborated by the observation that the sample's apparent viscosity decreased as the soy milk blend and shear rate increased in Figure 4.4 Similar observations were made by (Ikegwu & Ekwu, 2009) in their investigation of the rheological properties of achi dispersion As the shear rate (shear thinning) increased, the yoghurt samples' apparent viscosity decreased This finding is consistent with research conducted by (Alkali & Ijabo, 2003) on tomato paste and (Sopade & Kassum, 1992) on kunu gyada and kunu zaki Increased rotation causes molecules to align more in the direction of flow, which lowers viscosity and flow resistance This is why the shear thinning effect that is observed is expected This phenomenon is common with hydrocolloidal solutions and food paste that has a sensitive structure, according to (Awonorin, 1993)
4.2.3 Enumerating of L delbrueckii ssp bulgaricus in set yogurt supplemented with soymilk during fermentation
The enumeration of L delbrueckii ssp bulgaricus bacteria in 4 yogurt samples, including the control yogurt sample (CY) and yogurt samples supplemented with various soy milk contents of 25%, 50%, and 75%, respectively, to SY_25, SY_50, and SY_75, was detected by a 3M Petrifilm LAB Plate at the first point of fermentation and at the final point of fermentation Then, calculating the log CFU/mL value, which is shown in Table 4.3
Table 4 3 The number of L delbrueckii ssp bulgaricus in control yogurt and yogurt supplemented with soymilk
In both control and soy yogurt, the starter cultures inoculated with the tested strains grew well For SY_75, the number of viable cells after 260 minutes of fermentation reached to 3.62 × 10 8 CFU/g, and for control yogurt, it was 2.05 × 10 8 In SY_75, the amount of L delbrueckii ssp bulgaricus in the control yogurt (CY) was greatest and lowest, respectively It appears that soymilk, as opposed to skim milk, significantly (p