Effects of bacterial transformation of isoflavones and lignans in the antioxidant capacity

Polyphenols are compounds with high antioxidant capacity that play a crucial role protecting cells from damage caused by free radicals. Bacteria produce changes in the phenolic profile of plant foods, modifying their antioxidant capacity. The objective of this study was to understand the link between the antioxidant capacity of isoflavones and lignans and their bacterial derived metabolites, tested as pure compounds, and as products of the fermentation of soy beverages and flax extracts. Soy beverages and soy beverages supplemented with flaxseed fermented by Bifidobacterium pseudocatenulatum INIA P815 showed, mainly, a transformation of daidzin, genistin and secoisolariciresinol diglucoside into their aglycones daidzein, genistein and secoisolariciresinol. The fermentation of soy beverages produced an increase in the antioxidant capacity, measured by DPPH, and a decrease in the antioxidant capacity as measured by FRAP, ABTS and Folin-Ciocalteu. The fermentation of soy beverages supplemented with flax extracts produced an increase in the antioxidant capacity measured by DPPH and FRAP, and a decrease in the antioxidant capacity measured by ABTS and Folin-Ciocalteu methods. The deglycosylation reactions produced during the fermentation of soy beverages and soy beverages supplemented with flaxseed resulted in an increase in the DPPH values, just like the increase observed in the pure daidzein, genistein and secoisolariciresinol. This work demonstrates that the transformation of isoflavones found in soy by the gut microbiota into compounds such as equol and dihydrogenistein are accompanied by an increase in the antioxidant capacity by the different methods used, while the transformation of plant lignans into enterolignans usually produces a decrease in the antioxidant capacity.