PRODUCTION OF SOY YOGHURT USING SOYMILK-BASED STARTER CULTURE

Abstract

Production of soy-yoghurt by fermentation of soymilk with lactic acid bacteria was studied. Soymilk was extracted from dehulled soybean seeds and pasteurized at 95 OC for 15 min. The soymilk was left to naturally ferment (temperature; time?) and lactic acid bacteria were isolated, screened and selected for yoghurt production. Freshly prepared soymilk was pasteurized (95 °C, 15 min), inoculated with the lactic acid bacteria isolated (3% w/v starter culture) and incubated at 40 °C for 8 h. The yoghurt produced was stored at 4 °C. Commercial yoghurt was used as control. The percentage of soymilk inoculated was 70% of the broth. Soy-yoghurt samples produced were subjected to biochemical and microbiological analysis which included total viable counts of fresh milk and soy-based yoghurt; proximate composition of functional soy-based yoghurt fermented with Lactobacilus plantarum; changes in pH, Titratable acidity and Lactic acid bacteria during a 14 day period of storage; as well as morphological and biochemical characteristics of lactic acid bacteria isolated. The Lactobacillus plantarum isolated from soymilk was gram positive, catalase negative, indole negative, oxidase negative, spore forming negative and produced acid from glucose, fructose, galactose, raffinose, sucrose, maltose, mannitol, xylose, sorbitol and lactose. The results demonstrated that using Lactobacilus plantarum to inoculate soy milk for yoghurt production takes about 8 h. The overall acceptability of the soy-based yoghurt produced was not significantly different (P< 0.05) from that of the control sample. The use of isolate from soymilk had the added advantage of reducing the cost of yoghurt starter culture. Results from the present study have demonstrated a further way of enhancing soy yoghurt acceptability by the western ‘palate’.