Study on the preparation technology of Streptococcus thermophilus S10 starter for enhancing quality

Abstract

Streptococcus thermophilus S10 (S10) has good fermentation characteristics with a rapid fermentation rate and good acid-weakening capacity. However, low bacterial density and low activity in high-density culture limit its application. Aiming at the existing problems this study optimized the composition of S10 medium by one-way test and response surface design, and determined the formula of proliferation medium for S10. On this basis, the incubation temperature was optimized. After initial screening of the temperature of static culture, the optimum culture temperature was determined for a high-density culture in a parallel bioreactor. The results showed that the highest viable bacterial count in optimal medium was 1.79 ± 0.03 × 10⁹ colony-forming units (CFU)/mL at 38 °C. Samples of S10 fermentation broth cultured at 37 °C, 38 °C and 39 °C at high density were further inoculated with milk for validation of the fermentation capability. The results showed a faster acid production rate, the highest viable bacterial count, and enhanced fermentation in milk at 38 °C group, thus verifying that this was the optimal culture temperature for S10. The optimal medium composition and culture temperature determined in this study were associated with high biomass, high viable bacterial count, and good activity of S10, and our results constitute basic data for the development of this strain for use in industrial processing.