Lactobacillus bulgaricus KFCC 35463과 Kluyveromyces fragilis KFCC 35458 을 두유 배지에 접종하여 생육과 산생성의 특성을 조사한 결과 두유를 L. bulgaricus로 단독발효하는 것보다 K. fragilis와 혼합발효하는 것이 산생성량이 많고 산생성속도가 빨랐다. 이 두 균을 혼합배양하여 산생성을 높이기 위한 배양조건을 검토한 결과는 다음과 같았다. 두유에 sucrose를 1.0% 또는 탈지분유를 1.5% 첨가하고 L. bulgaricus와 K. fragilis 를 $O.;D._{660}$ 값으로 1 : 2가 되게 접종하여 $35{sim}37^{circ}C$의 온도에서 24시간 배양하는 것이 효과적이었다. L. bulgaricus를 단독 또는 K. fragilis와 혼합배양할 때의 산도는 각각 0.14%와 0.41%로서 혼합배양한 것이 2.9배 높았다. sucrose를 1.0% 첨가한 두유를 사용하였을 경우는 각각 0.13%와 0.70%로서 혼합배양한 것이 5.4배 높았다. 그리고 두유에 탈지분유를 1.5% 첨가하였을 경우는 단독해양한 것과 혼합배양한 것 모두가 0.84% 수준이었고 탈지분유를 1.5% 이하로 첨가하였을 때만 단독배양한 것보다 흔합배양한 것이 산도가 높았다.
Lactobacillus bulgaricus (KFCC 35463) and Kluyveromyres fragilis (KFCC 35458) were inoculated together in soymilk, and then growth characteristics, acid production and the conditions suitable for acid production were investigated. L. bulgaricus produced more acid and the rate of acid production was more rapid when this organism was incubated with K. fragilis in soymilk than when it was incubated singly. Studying the conditions suitable for acid production in soymilk, optimum acid production by the mixed cultures of L. bulgaricus and K. fragilis was achieved with a temperature of $35{sim}37^{circ}C$, a 1:2 (O.D.660) ratio of L. bulgaricus to K. fragilis at inoculum, a 1.0% level of sucrose fortification or a 1.5% level of skim milk powder fortification and a culture time of 24hr. Under these conditions the amount of acid produced by the single culture of L. bulgaricus and the mixed cultures of L. bulgaricus and K. fragilis were 0.14% and 0.41%, respectively, in soymilk, 0.13% and 0.70%, respectively, in soymilk fortified with 1.0% level of sucrose. These indicate that the amount of acid produced by mixed cultures is about 2.9-fold greater in soymilk and about 5.4-fold greater in soymilk fortified with 1.0% level of sucrose than that produced by the single culture of L. bulgaricus. The amount of acid produced in soymilk fortified with 1.5% level of skim milk powder was 0.84% level for both of the single culture of L. bulgaricus and the mixed cultures of L. bulgaricus and K. fragilis after 24hr incubation. However, the amount of acid produced by the mixed culture with K. fragilis was greater than that produced by the single culture of L. bulgaricus onlv in soymilk fortified with lower levels of skim milk powder than 1.5%.
