Enhanced in vitro and in vivo antioxidant activity and mobilization of free phenolic compounds of soybean flour fermented with different β-glucosidase-producing fungi

Aims:  To evaluate the soybean polyphenol glucosides bioconversion to aglycone forms by different β-glucosidases-producing filamentous fungi to enhance their antioxidant activity.
Methods and Results:  Soybean defatted flour was submitted to solid-state fermentation with Aspergillus niger , Aspergillus niveus and Aspergillus awamori . The fungi studied produced approximately the same β-glucosidase activity units amount when p- nitrophenyl-β- d -glucopyranoside was used as substrate for the assay. However, electrophoretic analysis, using 4-methylumbellipheryl-β- d -glucopyranoside as substrate, showed that β-glucosidase produced by A.   niveus was more active. Fermented methanolic extracts showed an increase in polyphenol and genistein contents and antioxidant activities. The highest genistein content was found in soybean fermented by A. niveus . Methanolic extracts of the soybean fermented by the different fungi showed a similar capacity of scavenging H₂O₂ generated in vivo by the tumour promoter 12- O- tetradecanoyl phorbol-13-acetate.
Conclusions:  A.   niveus synthesized a β-glucosidase with higher specificity to hydrolyse genistin β-glycosidic bond than those produced by A .  awamori and A. niger .
Significance and Impact of the Study:  The utilization of these β-glucosidases-producing fungi in soybean fermentation processes resulted in the obtaining of methanolic extracts with different antioxidant potentials that could be used either therapeutically or as an antioxidant in nonphysiological oxidative stress conditions, as the one induced in skin by UV radiation.