The trends in the TPC and ORAC assayswere in agreementwith each
other (Fig. 4). Comparing between the blank and control at day 0,
heating slightly increased the antioxidant capacity, which could be
due to the enhanced solubility of polyphenolic compounds and the
thermal degradation of isoflavones glycosides (with their aglycone
counterparts showing greater antioxidant capacity) (Tsubaki et al.,
2009).
Fermentation significantly improved the antioxidant capacity of
okara due to the degradation products of okara by the yeast, as yeast
biomass did not affect antioxidant capacity (data not shown). The
improvement in antioxidant capacity could be contributed by various
factors. Firstly, the increase in the amounts of certain amino acids
could have enhanced antioxidant activity. Hydrophobic and aromatic
amino acids, such as histidine, tryptophan and phenylalanine, have
antioxidant properties (Pownall et al., 2010). The increase in free
amino acid contents may also indicate the production of shorter chain
peptides, and the proteolysis of okara protein has been shown to release
potentially bioactive or antioxidant peptides