In the present context, we have assessed the green approach for the extraction of phenolics from agro-residues of rice viz., rice bran, and rice straw using water as an extracting solvent. The extraction was optimized with respect to time, temperature, pH, and solid (agro-residues) to liquid (water) ratio. The hydrolysates obtained were determined for phenolics and their antioxidant activities. The maximum total phenolic content (61.32 mg/100 g GAE), flavonoid content (13.19 mg/100 g QE), and tannin content (58.33 mg/100 g TAE) were obtained for rice bran followed by rice straw at pH 5, 1:20 (solid: liquid) for 10 min of extraction. Also, higher antioxidant properties (78.03% for DPPH, 86.45% for ABTS, and 0.85 absorbance at 700 nm for FRAP) were observed for the extracts of rice bran. Caffeic acid, gallic acid, p-coumaric acid, syringic acid, ferulic acid, 2,5-dihydroxy benzoic acid, kaemferol, quercetin, and epicatechin were analyzed by HPLC in both the rice biomass used. This study significantly converts rice biomass to antioxidative phenolic compounds under simple extraction conditions favoring the waste management process and also adding value to the waste biomass.
Keywords: Biomass valorization; natural antioxidants; phenolic compounds; rice biomass.