Bioactive metabolites, antioxidant, and antidiabetic activities of fermented local rice (Pare ambo) by Pleurotus spp.: in vitro and in silico approach

Pare ambo, a local black rice variety popular in Tana Toraja (South Sulawesi), is recognized for its health benefits, especially for those managing diabetes or aiming to prevent obesity due to its antioxidant-rich composition. This study explored the impact of Pleurotus spp. fermentation on pare ambo, examining its nutritional transformation. Proximate analysis indicated higher levels of crude protein (9.67+0.73%), crude fat (3.36+0.84%), and fiber (1.67+ 0.33%) in P. cystidiosus fermentation compared to P. ostreatus and P. djamor. Antioxidant and antidiabetic activities significantly improved in all fermentations at 500 ppm concentration. Pare ambo fermented by all three Pleurotus species contained citric acid and trimethyl ester compounds, displaying superior antioxidant and antidiabetic activities, interacting with antioxidant receptor 5O0x (-7.2 kcal/mol) and antidiabetic receptor 3w37 (-8.2 kcal/mol) compared to the unfermented sample. Fatty acid profiling identified 32 compounds, predominantly FAMEs with ester groups. Pleurotus cystidiosus and P. djamor fermentations contributed 20 compounds, while P. ostreatus contributed 18 compounds. Prominent interactions were visualized between naphthalene, and decahydro-2,6-dimethyl, with 5O0x and 3w37. Anthocyanins were detected through HPLC separation in P. cystidiosus and P. ostreatus fermentation outputs. This study shows pare ambo as a promising functional food, abundant in natural antioxidants and antidiabetic compounds, highlighting the potential of Pleurotus spp. fermentation to enhance the nutritional profile and bioactivity of indigenous rice varieties.