Studies on the mixed culture of Lactobacillus helveticus and Streptococcus thermophilus in milk - Growth characteristics and cultural conditions for the mixed culture -

Lactobacillus helveticus와 Streptococcus thermophilus의 혼합배양에 관한 연구 -생육특성 및 배양조건-

To investigate the new Yoghurt starter, Lactobacillus helveticus YM-1, which was selected among 14 Lactobacillus strains, and Streptococcus thermophilus CH-1 were inoculated together in reconstituted non-fat skim milk medium and their growth characteristics and cultural conditions for the mixed culture were examined. The main results of this study were obtained as follows. The typical symbiotic growth was shown between the two strains and pH and temperature for optimal growth were 6.5 and 4$0^{\circ}C$, respectively. Heat treatment of milk was most effective at 10$0^{\circ}C$ for 30 min. The cell-free filtrate of Lactobacillus helveticus YM-1 had stimulatory effect on Streptococcus thermophilus CH-1 but the reverse case was slightly observed. Significant difference was observed in the proteolytic activities between Lactobacillus helveticus YM-1 and Streptococcus thermophilus CH-1. The former liberated 135$\mu\textrm{g}$ free amino acid per $m\ell$ of cultured milk, the latter 35$\mu\textrm{g}$ per $m\ell$.

Lactobacillus helveticus YM-1 과 Streptococcus thermophilus CH-1을 환원탈지유 배지에 접종하여 생육특성 및 배양조건을 검토한 결과 두 균은 전형적인 공생을 나타냈으며 혼합배양시 최적 pH와 온도는 각각 6.5와 4$0^{\circ}C$였다. 또한 두 균 사이에는 단백질 분해력의 차이가 현저하였고 L.helveticus의 배양여액에는 S. thermophilus의 생육을 촉진시키는 물질이 함유되어 있음을 관찰하였다.