A metabolomics approach to evaluate post-fermentation enhancement of daidzein and genistein in a green okara extract

BACKGROUND Okara is a major agri-industrial by-product of the tofu and soymilk industries. Employing food-wastes as substrates for the green production of natural functional compounds is a recent trend that addresses the dual concepts of sustainable production and a zero-waste ecosystem. RESULTS Extracts of unfermented okara and okara fermented with Rhizopus oligosporus were obtained using ethanol as extraction solvent, coupled with ultrasound sonication for enhanced extraction. Fermented extracts yielded significantly better results for total phenolic content (TPC) and total flavonoid content (TFC) than unfermented extracts. A qualitative liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF-MS) analysis revealed a shift from glucoside forms to respective aglycone forms of the detected isoflavones, post-fermentation. Since the aglycone forms have been associated with numerous health benefits, a quantitative high-performance liquid chromatography (HPLC) analysis was performed. Fermented okara extracts had daidzein and genistein concentrations of 11.782 +/- 0.325 mu g mL(-1) and 10.125 +/- 1.028 mu g mL(-1), as opposed to that of 6.7 +/- 2.42 mu g mL(-1) and 4.55 +/- 0.316 mu g mL(-1) in raw okara extracts, respectively. Lastly, the detected isoflavones were mapped to their metabolic pathways, to understand the biochemical reactions triggered during the fermentation process. CONCLUSION Fermented okara may be implemented as a sustainable solution for production of natural bioactive isoflavonoids genistein and daidzein. (c) 2021 Society of Chemical Industry.

Automated summary

Okara, a by-product of the tofu and soymilk industries, was found to yield better results in total phenolic and flavonoid content after fermentation with Rhizopus oligosporus. Analysis showed a shift in isoflavones from glucoside forms to their respective aglycone forms post-fermentation, with fermented extracts having higher concentrations of genistein and daidzein, which are beneficial for health. The study suggests that fermented okara could be a sustainable solution for producing natural bioactive isoflavonoids.