In order to measure bacterial cell mass in fermenting milk accurately a new method including processes of dissolving milk curd and measuring dry weight has been develloped. Single strains of $\underline{Lactobacillus}$ $\underline{bulgaricus}$ and $\underline{Streptococus}$ $\underline{thermophilus}$ were cultured in 11 percent nonfat dry milk separately. When curd was formed, 1N-KOH solution was added until pH reaches 11.5 and shaked strongly to dissolve curd particles completely. Bacterial cells in the solution were separated by centrifuging three times including two times of washing with distilled water for 30 minutes at 3,000 R.P.M. The lactic acid producing properties of these two strains have been known to be growth associated. This growth associated characteristics was proved better with growth curves determined by the new dry weight method than that of conventional viable count method.
Using the new method effects of temperature on the growth of these two lactic starter strains in the milk was examined.
Optimum temperatures for the growth of $\underline{L}$. $\underline{bulgaricus}$ and $\underline{S}$. $\underline{thermophilus}$ were found to be 47℃ and 45℃, respectively. $\underline{L}$. $\underline{bulgaricus}$ responded more sensitively to the change of culture temperature than $\underline{S}$. $\underline{thermophilus}$ did. Through these experiments it was confirmed that the newly developed method can be used more conveniently and accurately for the measurement of bacterial cell mass in fermenting milk than any other existing methods.
우유에 있어서의 생장연구는 우유자체의 높은 탁도로 인해 탁도측정법을 사용할수 없고 유산균들의 사슬형성 성격으로 인해 생균수 측정방법을 사용함에 있어 그 정확도를 기하기 어려운 이유로 해서 많은 진전을 보지 못했다. 저자등은 가장 정확한 생장 연구 방법인 건조 중량법을 우유에서도 적용되게끔 순수한 균분리 방법을 연구했다. 유산균에 의해서 생성되는 유산에 의해 응고되는 유단백질을 가용화시키는 것이 주된 요점이 되므로 이에대해 연구한 결과 우유를 1N-KOH 로 산도 11.5 부터 12.0 사이로 맞추면 완전히 용해되며, 이를 1500g 에서 30분 원심분리 시키면 일정한 양의 비수용성 단백질과 균체가 침전되는 것을 발견했다. 이 방법으로 $\underline{Lactobacillus bulgaricus}$ 와 $\underline{Streptococcus}$ $\underline{thermophilus}$ 의 온도에 있어서의 성장과 산 생성율에 대한 연구를 했다.