Optimized cultural conditions of functional yogurt for γ-aminobutyric acid augmentation using response surface methodology.

Yogurt, a functional dairy food product, is an effective medium for delivering beneficial functional ingredients. One ingredient, γ-aminobutyric acid (GABA), has growing appeal in the development of functional foods for its potential in reducing the risk of diabetes, hypertension, and stress as a bioactive agent. However, the concentration of GABA in existing food products is remarkably low. We developed a functional yogurt rich in GABA using Streptococcus thermophilus fmb5. The GABA yield of yogurt was enhanced by optimization of culture conditions using single factor and response surface methods. The results showed that culture temperature, monosodium glutamate concentration, and culture time are the 3 main factors that affect GABA yield. The optimal culture conditions were determined as follows: 38.8°C for culture temperature, 20 g/L of monosodium glutamate, and 120 h of culture time. Under the above optimal conditions, the actual yield of GABA production was maximized at 9.66 g/L, which was 1.2 times or higher than that of from any single factor treatment. The GABA concentration, viable bacteria number, and water-holding capacity of GABA-rich yogurt were stable throughout the whole storage time. The results show that producing yogurt with Streptococcus thermophilus fmb5 and the optimized culture conditions will achieve high GABA concentrations that maximize health benefits to consumers.