ABSTRACT

This research was done to determine the microbes present and the nutritional changes that occur when soybean is thermally processed to soymilk and then fermented to soy yogurt using starter cultures. The soybean was purchased from ubani central market in umuahia, Abia state. It was de-hulled, boiled and thermally processed to soymilk. The soymilk was then fermented to soy yogurt for 12 hours using starter cultures (lactobacillus spp and streptococcus thermophilus), sweetener (Glucose -D) and cassava stabilizer. Standard microbiological characterization of the isolates was carried out. Results revealed that the bacterial isolates from the raw soybean are: Staphylococcus aureus, Bacillus spp, Escherichia coli, and Lactobacillus spp. The fungal isolates from the raw soybean are Aspergillus spp and Saccharomyces spp. The soymilk had no microbial isolate because it was pasteurized for 20 minutes at 850C. The microbial isolates of the soy yogurt from the 0hr to the 12 hr were Lactobacillus spp and Streptococcus thermophilus. The moisture content determined by the AOAC method showed that soymilk had the highest value (82.16%) which was followed by the soy yogurt (80.35%) and the lowest was the raw soybean (8.00%). The crude protein determined by Kjeldalh method showed that raw soy bean had the highest value at (41.00%) which was followed by soy yogurt (7.87%) and soy milk (5.00%).  The crude fiber determined showed that raw soy bean had the highest value (4.00%) which is followed by soy milk (0.07%) and the soy yogurt (0.02%). The fat was determined using the AOAC method showed that the raw soy bean had more fat content (19.00%) than the soymilk (4.00%) and the soy yogurt (3.35%). The ash content showed that the raw soybean had high ash value (19.00%) followed by the soymilk (0.77%) and the soy yogurt (0.55%). The carbohydrate using the AOAC method showed that the raw soybean had the highest value (21.00%) which was followed by the soymilk (8.00%) and then the soy yogurt (7.86%). The proximate composition showed that the soy yogurt had more protein content than soymilk. However, the soymilk had more crude fiber, moisture content, fat content, ash content and more carbohydrate. The %TTA was determined by the alkaline titrimetric method which showed that the soy yogurt (1.81) is more acidic than the soy milk (0.11). The pH was determined using Hana size pH meter which showed that the soy yogurt is more acidic (3.7) than the soy milk (6.4). The acidity of the soy yogurt prevents the activities of food spoilers and pathogens that might have access to the soy yogurt.  From this study it can be concluded that fermented soy bean (soy yogurt) using starter cultures is more proteinous and has less fat than soy milk and also has comparable carbohydrate content with the soy milk. The fermented processed soybean seed (soy yogurt) contains lactobacillus spp and streptococcus spp which are classified as friendly bacteria and are beneficial to the human health.