CHEMICAL AND MICROBIAL PROPERTIES OF YOGURT PROCESSED FROM COW'S MILK AND SOYMILK

Yogurt was processed by inoculation of cow's milk and soymilk with freeze-dried culture of Lactobacillus bulgaricus and Streptococcus thermophilus. The processed yogurt samples were evaluated for chemical microbial and organoleptic properties using an existing commercial yogurt as control. The moisture content of the yogurt samples ranged from 83.3% in cow's milk yogurt to 91.9% in soymilk yogurt. Soymilk yogurt was significantly high in protein (6.6%). Fat and ash were highest in cow's milk yogurt: 6.5% and 0.6%, respectively. There was no significant difference (P < 0.05) in the magnesium content of all the yogurt samples. pH ranged from 4.1 in cow's milk yogurt to 5.4 in soymilk yogurt. The total viable count was highest in cow's milk yogurt (1.1 x 10⁵). The major bacteria isolated in all the yogurt samples were L. bulgaricus and S. thermophilus. Soymilk yogurt compared favorably well with commercial yogurt in overall acceptability. Soymilk yogurt is a good alternative to cow's milk yogurt. Chemical and microbial properties of yogurt processed from cow's milk and soymilk established the context and contents of choosing yogurt as healthy food for the people. Soy yogurt can be adopted as substitute to cow's milk yogurt especially by the low income earners due to its cheaper raw materials, and as protein supplement at household level. Soy yogurt requires boiling at 100C, cooling (45-50C), inoculation with culture, fermentation (6-12 h), mixing, addition of fruit flavor, and is served in cups. It can be stored in the refrigerator at 5C for 72 h or at ambient temperature for 24-48 h. The utilization of soy yogurt as household food/drink is a result of its nutritional compositions, absence of cholesterol, high protein content and its raw materials being accessible within the household resources and can also be processed with simple processing technology.