Enrichment of Functional Characteristics in the Okara by the Fermentation of Rhizopus azygosporus

PURPOSE: Okara is a solid waste of soybean-processed foods; it is normally used as a low-priced product, such as fertiliser and feed. An alternative method for the convertion of okara to valorized products is required. METHODS: This research employed Rhizopus azygosporus with fast-growing property to ferment bean dregs using solid-state fermentation technology and examined the functional composition and the physiologically effective bioactivities for comparison with unfermented okara. RESULTS: Rhizopus oligosporus BCRC 33956 and R. azygosporus BCRC31158 were cultivated on potato dextrose agar plates for 72 h after which they were used for comparison, and R. azygosporus exhibited approximately 1.3 times of growth rate than R. oligosporus. The contents of γ-aminobutyric acid (GABA) and crude polysaccharide in two days ferment accumulated to 696 mg/kg and 40.6%, respectively. During fermentation by R. azygosporus for 2 days, 74.6% genistin, a type of isoflavone glucoside, was depleted and 106.7 mg/L genistein was detected in the extracts. The results also showed that the proliferation of R. azygosporus enhanced several bioactivities in the okara fermentation. The relative angiotensin-converting enzyme inhibitory effects in the extracts of unfermented and fermented okara were 74.9% and 132.3%, respectively, compared with those of 10 mM captopril. The antioxidant capacity, including free radical scavenging activity and reducing power, was also significantly increased in okara accompany the growth of R. azygosporus. An animal study showed that GABA and functional characteristics and contents enriched by R. azygosporus in the okara fermentation were likely to have an obvious synergistic effect on the reduction of cortisol concentration in stimulated zebrafish, revealing the anti-stress function of fermented okara. Our work provides the process for development as a functional product, especially in anti-stress, which will further increase the value of okara and reduce waste, enabling sustainable consumption and production patterns.