Abstract
Isoflavones of soy milk were mainly present as sugar conjugates such as genistin and daidzin which a glucosyl residue was attached to their aglycones, genistein and daidzein through ${\beta}-glycosidic$ bond, respectively. When soy milk containing sucrose as a sugar source was fermented with lactic acid bacteria, small amount of lactic acid $(0.16{\sim}0.29%)$ was produced but isoflavone conjugates were fully hydrolyzed. Supplementation of glucose or lactose was required for normal lactic acid production and affected the hydrolysis of isoflavone conjugates in some lactic acid bacteria. In the case of Lactobacillus delbrueckii subsp. delbrueckii KCTC 1047, glycosidic bond of isoflavone was fully hydrolyzed regardless of glucose supplementation. But only $25{\sim}40%$ of daidzin and $65{\sim}80%$ of genistin was hydrolyzed when glucose was added into soy milk in the other lactic acid bacteria, Lactobacillus bulgaricus KCTC 3188, Lactobacillus casei KCTC 3109, Lactobacillus delbrueckii subsp lactis KCTC 1058, Lactobacillus lactis KCTC 2181. The hydrolyzing enzyme, ${\beta}-glucosidase$ produced by lactic acid bacteria except Lactobacillus delbrueckii subsp. delbrueckii KCTC 1047 could be considered as inducible in the fermentation of soy milk and its production was decreased when glucose was added.
두유에 존재하는 이소플라본은 주로 포도당 잔기가 aglycone인 genistein과 daidzein에 ${\beta}-glycoside$ 결합을 하고 있는 배당체인 genistin과 daidzin이다. 두유에 설탕을 첨가하여 유산균으로 대두 요구르트로 발효를 시키면 젖산의 생성은 매우 낮아 약 $0.16{\sim}0.29%$에 불과하였지만 대부분의 이소플라본 배당체가 가수분해되어 aglycone으로 전환되었다. 포도당이나 젖당을 첨가하여 발효시키면 정상적인 젖산발효는 일어났지만 이소플라본 배당체의 가수분해는 균주에 따라 변하였다. Lactobacillus delbrueckii subsp. delbrueckii KCTC 1047은 당의 첨가와 무관하게 이소플라본 배당체를 완전히 가수분해시켰다. 그 밖의 균주는 daidzin은 약 $25{\sim}40%$, genistin은 약 $65{\sim}80%$ 정도만을 가수분해시켜 이들 당에 의해 가수분해가 감소하였다. 즉 Lactobacillus delbrueckii subsp. delbrueckii KCTC 1047을 제외한 Lactobacillus bulgaricus KCTC 3188, Lactobacillus casei KCTC 3109, Lactobacillus delbrueckii subsp lactis KCTC 1058, Lactobacillus lactis KCTC 2181과 같은 균주의 경우 이소플라본 배당체의 가수분해에 관여하는 효소인 ${\beta}-glucosidase$가 유도 효소로 포도당이나 젖당에 의해 생산이 저해되었을 것으로 예상된다. 또한 MRS 배지에서 배양하였을 때에도 Lactobacillus delbrueckii subsp. delbrueckii KCTC 1047만이 이 효소를 생산하였다.
(Department of Food Science and Technology, Dongguk University)