Influence of temperature and glucose addition on growth and survival of bacteria from BCT culture in soymilk

Soymilk was fermented using culture composed of Lactobacillus casei, Bifidobacterium spp. and Streptococcus thermophilus (BCT culture, Chr. Hansen’s, Denmark) at two temperatures 37 °C and 41 °C with and without 5 % of glucose addition. Fermentation was conducted until pH value 4.6 was reached. During fermentation and storage time (28 days at +4 °C) changes of pH values and viable cells counts were observed. All fermentations lasted between 6 and 7.5 hours. At temperature 41 °C fermentation was approximately 1 hour shorter, while glucose addition had reduced fermentation time for 30 minutes. Higher temperature of fermentation, as well as glucose addition, had negligible influence on portions and viable cells count of particular bacterial species in the product. In all fermented soymilk samples the viable cells count of particular bacterial strains was roughly equal: Str. thermophilus have grown the best (~ 108 CFU/mL) while lactobacilli have grown the weakest (~ 105 - 106 CFU/mL). Generally, for soymilk fermentation mainly Str. thermophilus was responsible. On its growth rate glucose addition and higher fermentation temperature had strong positive influence. During 28 days of refrigerated storage, the product was stable. A remarkable decrease of viable cells count of lactobacilli was noticed in the last week of storage.