Growth of bifidobacteria in soymilk and their survival in the fermented soymilk drink during storage.

Growth of Bifidobacterium infantis CCRC 14633 and B. longum B6, in soymilk was investigated in the present study. It was found that soymilk could support the growth of both organisms tested. B. infantis grew better than B. longum in soymilk. Supplementation of bifitose (isomaltooligosccharie), glucose, lactose or galactose to soymilk increased the growth of B. infantis and B. longum as determined after 48 h of fermentation. On the other hand, addition of yeast extract, peptone, tryptone, casitone or N-Z-Case plus to soymilk enabled B. infantis to reach its maximum population in a shorter cultivation time of 24 h. Acid production by B. longum and B. infantis in soymilk was mainly non-growth associated, while in the yeast extract-supplemented soymilk, acid produced by B. infantis was found to be growth-associated. Populations of B. longum reduced more than did B. infantis in the prepared fermented soymilk drink during storage period. Viable population of both test organisms reduced less in the fermented drink held at 5 degrees C than at 25 degrees C. After a 10-day storage at 5 degrees C, viable B. infantis and B. longum reduced by 0.44 and 3.18 log CFU/ml, respectively, in the fermented drink. Addition of sucrose to the fermented drink resulted in an increased reduction of viable bifidobacteria during the storage period. This phenomenon was most prominent with B. infantis in the fermented drink held at 25 degrees C.