Phenolic Antioxidant Enrichment of Soy Flour-Supplemented Guava Waste by Rhizopus Oligosporus-Mediated Solid-State Bioprocessing

In this paper, we investigated the potential for Rhizopus oligosporus to produce enhanced levels of free phenolics from guava residue mixed with soy flour as the nitrogen source.β-glucosidase activity and antioxidant activity in crude extracts were evaluated. Two substrates were studied based on carbon and nitrogen ratios: A, 90% guava residue : 10% soy flour (G9) and B, 50% guava residue : 50% soy flour (G5). Bioprocessing increased water extractable phenolics 12.9% with G9 substrate and 98.6% with G5 substrate. For both substrates, antioxidant activity increased during early stages of fungal growth but decreased thereafter. Phenolic antioxidant mobilization during bioprocessing was associated withβ-glucosidase activity and hypothesized to involve the mobilization of polymeric phenolics. The bioconversion of soy flour-supplemented guava residue by R. oligosporus represents a novel strategy for the enhancement of phenolic antioxidant content and potential commercial value of guava wastes.