CARBOHYDRATE UTILIZATION and GROWTH KINETICS IN the PRODUCTION of YOGURT FROM SOYMILK. PART II: EXPERIMENTAL and PARAMETER ESTIMATION RESULTS

Typical yogurt bacteria, Lactobacillus bulgaricus and Streptococcus thermophilus, have been studied for their ability to utilize stachyose and other sugars in soymilk. Subculturing of the inocula on nonfat dry milk powder (NFDM) yielded bacteria that displayed oligosaccharide formation during fermentation of soymilk. However, storage of stock cultures on soymilk for 168 h or longer resulted in stachyose hydrolysis during fermentation. Values of the maximum specific growth rate for mixed cultures of Lactobacillus bulgaricus and Streptococcus thermophilus grown on soymilk at 44°C were estimated using the covariate adjustment method which allows biomass, substrate, and product data to be employed, simultaneously. Point estimates were 0.341, 0.296, and 0.478 h−1 for soymilk fermentation by inocula subcultured on 11% NFDM, for inocula stored in soymilk for greater than 168 h, and for inocula prepared as a mixed culture, respectively. the available electron balance (A.E.B.) was employed to check the consistency of the data using biomass, substrate and product measurements.