Physicochemical and Microbial Content Determination of Soycheese (Tofu) Using Selected Coagulants
Objective of the Study
The objective of this study is to determine the physicochemical and microbial content determination of soy-cheese (Tofu) using selected coagulant (lime, pap water and alum).
Tofu is a water extracted and salt or acid coagulated soy protein gel, with water, soy lipids and other components trapped within the network. Depending on the method of preparation used, the textural properties and composition of commercial Tofu may vary. They are generally classified as dey tofu (Doufugan), firm tofu (Momen), soft tofu (Kinu), and filled (packed), tofu (Liu and Chang, 2004).
In traditional method of preparing tofu, soybean are washed, soaked and then ground with added water. The resultant slurry is then filtered. This filtrate is collected to become a raw soymilk. The milk is then heated before a coagulant is subsequently added to form a curd or tofu. The ‘firm’ and ‘soft’ tofu are made by pressing after coagulation to remove any excess whey, but the ‘silken’ and ‘soft’ tofu are made without the removal of the whey after coagulation (Liu and Chang, 2003; Liu and Chang, 2004; Chang et al., 2005). Therefore, silken tofu and filled tofu have the highest water content and soft.
Complex interactions of many contributing factors occur in the making of tofu. The processing methods play a major role on the tofu yield, moisture content, hardness and elasticity of the end product. In practice increasing the soymilk concentration give a ‘harder’ tofu (Chang et al., 2005).
Factors affecting tofu manufacture
The quality of tofu is influenced by the quality of soymilk depends on the variety of soybeans used and the condition of soymilk preparation. The coagulation process depends on the concentration and temperature of soymilk, the type and relative amount of coagulation and the mixing method and time. The protein content in the raw soybean material is usually considered to be the most important factors in determining the quality of soymilk extracted and acceptability of the final tofu produced. The correlation between the protein content of the soybean and soymilks and between the content of soybean protein and the total solid content of soymilk are significant (Min et al., 2005). The hardness of filled tofu increases with protein content in soymilk (Shen et al., 2001).
The amount and type of coagulant added to soymilk are critical factors in tofu making as they particularly change the textural properties of the tofu produced. The amount of coagulant required is positively correlated with the phytate content, pH, and 7s protein content but negatively correlated with the overall protein content, 11s protein content, 11s/7s ratio, titrate acidity and calcium content in the original soymilk within the same soymilk material, higher protein levels require the use of more coagulant, however, a higher protein concentration during heating resulted in less coagulant being required by each gram of protein during coagulation. Different sequence of heating and dilution of the protein has resulted in different coagulant requirements (Liu and Chang, 2004).
When a suitable amount of coagulant is used, whey becomes transparent with an amber or pale yellow colour and a sweet taste. There should remain no uncoagulated soymilk protein in the whey.
Generally in the tofu making, soymilk must be properly heated before adding coagulant. This heat treatment is essential not only for improving nutritional quality and reducing the ‘beany’ flavour but also for denaturing the proteins, so that they can coagulate into curd in the presence of the coagulant. Variations in the temperature and time of heating soymilk before adding coagulant to make tofu have been reported in the literature. This includes, heating to 90°c and held for 5 minutes (Kao et al., 2004), heating to 85°c for at least 5 minutes (Weaver et al., 2002).
Coagulant of soy cheese
The milk clotting properties are of great importance with regards to both yield and the organoleptic quality of the cheese. The shelf life, nutritional composition, sensory quality and quantity of cheese produced are consequently affected by the type of coagulants used. The coagulants can be enzymes, salts or acids and recent studies have investigated cold-type coagulants. Scientists in cheese industry have been looking for improved coagulation methods of soymilk by altering and optimising the concentrations of coagulating process, aiming upgrade the quality of texture and flavour and increase the yield of soy cheese increasing the coagulant concentration tends to decrease the fat content of soy cheese (Jayasena et al., 2014).
Traditional soymilk cheese type
Tofu is a white soft vegan cheese that originated either in China or the Islands around Okinawa in about the 1500’s (Shurtleff and Aoyagi, 2013). Traditional tofu has two main categories, soft and hard types and can be pickled or land stinky. Pickled tofu is soaked in brine, vine, vinagar or other flour mixtures as dry cubes. Stinky-type tofu is soft type made using fermented milk, meat, vegetable, dried shrimp amaranth greens, mustard greens, bamboo shoots and herbs. This type has no specific starter and uses these aforementioned ingredients to introduce the naturally occurring starters that are present in traditional food product. This stinky tofu has a strong pungent odour that is described as rotten or fecal. Different types of tofu have been manufactured by Chinese from centuries ago and the manufacturing conditions were depended on the geographical area of China (Han et al., 2001).
Although sufu was originally a fungal fermented product, bacterial fermentation is also possible (Liu et al., 2006). Sufu can be commonly seen as the type of red, white and grey in China. Ethanol and NaCl are the basic components of tofu, which balance the traditional flavour and render the product safe against pathogenic microorganisms (Han et al., 2001)
Historical aspect of Tofu
It is believed that the soybeans has originated from China nearly 4000-5000years ago and was used as a popular product in Chinese cuisene. China was the world’s largest producer of soybeans and it exports till 1954 until United States succeeded them. China being the birth land of tofu, it gave the name originally called as Doufu, documented by Taoku in 950 A.O. the term tofu was however, coined by Japanese in early 1182. During the developmental period of tofu in 14 century.
MATERIALS AND METHOD
Soybeans (Tofu) used for this study was collected and purchase from Nepa market, Akure Ondo State, Nigeria. In a polythene bag and taken to the laboratory of the department of food science and technology is carrying out the hypothesis.
Traditional processing of fresh Tofu
The procedure for the processing of soybean includes manual sorting of the beans, washing and it was soaked for 8-10 hours until they are completely hydrated. The unabsorbed water remaining after soaking was drained off. The hydrated beans are then combined with fresh water and wet milled. The resulting slurry was filtered using a muslin cloth, washing with water and pressed to remove any remaining soymilk and insoluble residue (Okara). The Okara was pressed, washed and then pressed again to remove any remaining soymilk. It was then cooked at 100°c for a period of time, usually 7-10 minutes.
The soymilk was then coagulated with some sour liquid or residue from making pap (steep water). To produce the finished tofu, the curds are separated from the whey, poured into a muslin cloth-pressing box, pressed for a period of time and then cooled. The production of soy milk is one of the most important phases in tofu production. The tofu was further divided into two: one part was cold as fresh firm tofu while the other part was stored for further processing.
RESULTS AND DISCUSSION
Table 4.1: Results of the physical properties of soy cheese (Tofu) using selected coagulant
CONCLUSION AND RECOMMENDATIONS
The result of this study shows that sample A (potassium aluminium sulphate) was a better coagulant when compared with other coagulants used in the production of soycheese (tofu) in terms of yield, hardness, pH and dry matter. The result of microbial suggests that the use of lime as coagulant in the production of soycheese (tofu) will give the product a longer shelflife. Tofu represent a product of soybean mostly consume for its protein content. It is used in various culinary dishes and health food for its nutritious property and wholesomeness.
Tofu is majorly manufactured by the unorganized sector using traditional methods which leads to unequal quality as there are no set standards of tofu. It can also prove to be our most efficient weapon against global hunger and malnutrition problems provided sufficient efforts are made to popularize it’s nutritional significance among masses and efforts are made to develop technologies for it’s industrial production.
Further studies should be done on the processing method and fortification of soybean with some legumes for the production of tofu to increase its nutrient bioavailability.
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