Impact of fructose and fructooligosaccharides supplementation upon the fermentation of hydrolyzed okara and its impact upon bioactive components

Okara provide compounds of biological interest such as isoflavones and an increase of aglycone content can be obtained through fermentation with foodgrade bacteria. This study aimed to evaluate the effect of fructose and fructooligosaccharides (FOS) on the growth of probiotic bacteria in hydrolyzed (by Cynara cardunculus enzymes) okara beverage, as well as on the antioxidant activity, isoflavones and total phenolic content of fermented okara beverage. Okara beverages were fermented using Bifidobacterium animalis ssp. lactis Bb-12 and Lactobacillus rhamnosus R11 alone or as mixture of both, at 37 ºC, until it reached a pH value of 4.5. The growth of lactobacilli and bifidobacteria was evaluated throughout the fermentation, with increases of viable cells ranging from 1.5 to 3 log CFU/mL. Moreover, okara samples supplemented with a carbon source presented a higher growth rate than their non-supplemented counterpart, as expected. In addition, significant differences in aglycone content and antioxidant activity were observed for the okara samples fermented by different species, with the overall content of isoflavone aglycones increasing, the genistein presented the highest increase (ca. 16-fold) in the fermented okara by B. animalis ssp. lactis Bb-12. However, the antioxidant capacity was maintained in the okara without carbon source after fermentation by L. rhamnosus R11, while all fermented okara presented a decrease after fermentation process. Considering the hereby reported results, probiotic hydrolyzed fermented okara can be considered a good carrier for probiotic bacteria and a good source of aglycone isoflavones, combining all the other benefits resulting from probiotic metabolism and the hydrolyzed okara itself.