Production of set-type yogurt fortified with peptides and γ-aminobutyric acid by mixed fermentation using bacillus subtilis and Lactococcus lactis

Abstract

Mixed fermentation of cow milk was performed by sequential co-cultures with Bacillus subtilis and Lactococcus lactis. After a first fermentation step with B. subtilis for 6 h, the number of viable cells increased to 2.5 × 10 8 CFU/mL. The second fermentation step with L. lactis resulted in increased viable cells 1.09 × 1010 CFU/mL for 3 days and increased acidity. However, the number of viable B. subtilis cells was decreased greatly to 5 × 101 CFU/mL following fermentation with L. lactis. Milk proteins were markedly hydrolyzed by the first fermentation after 2 h, and the second fermentation induced curd formation in milk. However, after 4 h, the first fermentation resulted in higher whey separation and 80 mg% tyrosine content. Gamma-aminobutyric acid (GABA) production was dependent upon the degree of protein hydrolysis by first fermentation. Second fermentation resulted in 0.14% GABA. The milk fermented by B. subtilis indicated the rough surface of yogurt depended upon the degree of protein hydrolysis. In conclusion, set-type yogurt was efficiently produced by co-culturing of milk, and fortifying with peptides, GABA, and probiotics. copyright © 2014 The Korean Society of Food Science and Technology.