Efficacy from Different Extractions for Chemical Profile and Biological Activities of Rice Husk

Rice husk is a by-product produced abundantly in rice production but it has low commercial value and causes environmental pollution. This study was conducted to examine different extracting solvents and conditions to optimize the efficacy of antioxidant and antimicrobial potentials, and chemical components in rice husk. By the use of distilled water at 100 °C, the ethyl acetate (EtOAc) extract was potent in both total phenolic content (TPC), total flavonoid content (TFC), and DPPH scavenging activity. The treatment of either ethyl acetate (100 °C, 1 h), combined with MeOH 100%, showed the highest percent of lipid peroxidation inhibition (LPI) (86%), meaning that the strongest antioxidant activity was by the β-carotene bleaching method. The treatment of distilled water at room temperature possessed the strongest antioxidant activity in the assay of the reducing power. The use of dried samples at 100 °C for 2 h, combined with methanol (MeOH) 10%, provided the most potent antimicrobial activities against Escherichia coli , Klebsiella pneumoniae , Listeria monocytogenes , Bacillus subtilis , and Proteus mirabilis . The results suggested that the EtOAc extract from rice husk could be a potential source of natural antioxidants. In general, the use of temperature 100 °C for 2 h, combined with either EtOAc or 10% MeOH, can optimize chemical components and antioxidant and antimicrobial capacities in rice husk. Principal constituents putatively identified by gas chromatography–mass spectrometry (GC–MS) revealed the presence of momilactones A and B (MA and MB, respectively), phenols, phenolic acids, and long-chain fatty acids, although yields of these compounds varied among extracts. The bioactive MA and MB were found in most of the extracts, except distilled water and MeOH ≤ 50%, at any temperature. Findings of this study provided optimal conditions for future production at an industrial scale for rice husk to exploit its potent biological properties. It thus helps to increase the economic value and reduce the disposal burden and environmental troubles caused by rice husk.