Aglycone production by Lactobacillus rhamnosus CRL981 during soymilk fermentation.

Lactobacillus rhamnosus CRL981 showed the highest levels of beta-glucosidase and was selected to characterize this enzyme system, among 63 strains of different Lactobacillus species. The maximum activity was obtained at pH 6.4 and 42 degrees C. The enzyme showed weak resistance to thermal inactivation maintaining only 20% of the initial activity when it was exposed at 50 degrees C for 5 min. It also, showed stability when stored at 4 degrees C for 60 days. Afterwards, L. rhamnosus was evaluated for hydrolysis of isoflavones to aglycones, cell population, residual sugars and organic acid produced during fermentation on soymilk (37 degrees C for 24 h). Higher viable counts were obtained after 12 h of fermentation (8.85 log CFUml(-1)) followed by a drop of pH and an increase of acidity during fermentation due the production of organic acids. L. rhamnosus CRL981 was able to proliferate in soymilk and produce a high beta-glucosidase activity achieving a complete hydrolysis of glucoside isoflavones after 12 h of fermentation. The present study indicates that L. rhamnosus CRL981 could be used in the development of different aglycone-rich functional soy beverages.