Extraction of phenolic compounds from rice husk via ethanol-water-modified supercritical carbon dioxide

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Supercritical carbon dioxide, Ethanol, Water, Extraction, Rice husk, Phenolic compounds


Rice husk, a rice processing byproduct generated in large quantities (∼20% of the grain weight), creates a major disposal problem for the rice industry. However, rice husk contains high-value bioactive compounds that can provide potential health benefits. The objective of this study was to extract high-value phenolic compounds from rice husk using supercritical carbon dioxide (SC–CO2) technology. In this study, the effects of different extraction conditions, namely, temperature (40 and 60 °C), pressure (30 and 40 MPa), and ethanol concentration (15 and 25%, w/w) on the total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity (AA) were investigated. The extraction of phenolic compounds was also studied using different SC-CO2 modifiers, i.e., ethanol and ethanol-water. The highest TPC, TFC, and AA were achieved with 30 MPa, 60 °C, and 25% ethanol-water (50%, v/v) cosolvent mixture as 1.29 mg gallic acid equivalent (GAE)/g, 0.40 mg catechin equivalent (CE)/g, and 0.23 mg Trolox equivalent (TE)/g, respectively. Increasing water content up to 50% (v/v) in the cosolvent significantly improved the extraction yield. p-Coumaric, ferulic, and syringic acids were the predominant phenolic acids in the extracts obtained by cosolvent-modified SC-CO2 and methanol extractions. In addition, ethanol-water-modified SC-CO2 increased rice husk's porosity, which could be a potential pretreatment to enhance cellulose extraction. Thus, ethanol-water-modified SC-CO2 can be utilized to recover polar bioactive compounds from food processing byproducts for developing functional foods while eliminating the use of toxic organic solvents.


This article was published with support from the Open Access Publishing Fund administered through the University of Arkansas Libraries.