Okara is a major agro-waste, generated as a byproduct from the soymilk and tofu industry. Since okara has a high nutritive value, reusing it as a substrate for solid state biofermentation is an economical and environmental friendly option. Rhizopus oligosporus and Lactobacillus plantarum were the probiotic FDA-approved food-grade cultures used in this study. The study revealed that biofermenting okara improves its nutritional composition. It was found that the metabolomic composition (by GC-MS analysis) and antioxidant activity (by DPPH test) improved after the microbial fermentations. Of the two, okara fermented with R. oligosporus showed better results. Further, the metabolites were traced back to their respective biosynthesis pathways, in order to understand the biochemical reactions being triggered during the fermentation processes. The findings of this entire work open up the possibility of employing fermented okara as a potential functional food for animal feed.

Extracts were extricated from raw okara and okara fermented with Rhizopus oligosporus using a clean, green protocol; water was used as the extraction solvent and coupled with ultrasound assistance for enhanced extraction. In vitro anti-oxidant analyses for antioxidant potential and capacity, superoxide scavenging activity, and nitric oxide scavenging activity validated that fermented okara yielded superior bioactive performance compared to raw okara. Fermented okara extracts showed no toxicity to erythrocytes and successfully prevented induced haemolysis. After 48 h incubation at the highest tested concentration (100 mg/mL), fermented okara extracts could inhibit HepG2 cells by 48.47 ± 5.28%, which was significantly different from their effects on NIH 3T3 cells. Gas chromatography–mass spectrometry characterization of extracts validated amino acids to be the chief fraction responsible for the detected bioactivity of the fermented okara extract. The results derived in this study open up the possibility that biofermented okara extract may be a potential novel sustainable nutraceutical.

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 μg mL–1 and 10.125 ± 1.028 μg mL–1, as opposed to that of 6.7 ± 2.42 μg mL–1 and 4.55 ± 0.316 μg 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. © 2021 Society of Chemical Industry.

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I credit my Supervisor, Professor Chen Wei Ning, William, for being the guiding force behind my PhD. His invaluable advice and the degree of freedom that he permitted me were indispensable to this work. I am also deeply grateful to my Co-supervisor, Associate Professor Cao Bin and my Mentor, Associate Professor Thirumaran Thanabalu for their unwavering support and encouragement throughout my candidature. I am indebted to my wonderful labmates for providing the best-est environment to work in. Jas, you were my rock from Day 1. Truly appreciate Xiaomei and Guili for always ordering my consumables, and Jianhua, my cell culture teacher. Kuan Rei, Jae (my BL-in-crime!), Ting Shien, Wai Kit and Yong Xing, thank you for all the jokes, conversations and company.Sincere thanks to the staff from SCBE and NEWRI -Jessica, Chea Boon, Dr.