Properties of rice stem extracts obtained by subcritical water/ethanol treatment

Abstract

Rice straw stem was treated with subcritical water, ethanol, or a mixture at 170°C to 230°C. The yield, total carbohydrate content, UV-Vis absorption spectra, phenolic content, radical scavenging activity, and HPLC analysis of the extracts were determined. Higher stem extract yield and total carbohydrate content were achieved when the stem was treated using a subcritical ethanol/water mixture with high ethanol content and at the higher temperature. A maximum yield and total carbohydrate content of 0.387 ± 0.004 g/g-stem and 0.219 ± 0.021 g/g-stem, respectively, were achieved when the stem was treated with 50% (v/v) ethanol at 230°C. The extract obtained using 75% (v/v) ethanol at 230°C had the highest total phenolic content and radical scavenging activity of 45.2 ± 1.1 mg-gallic acid equiv./g-stem and 0.308 ± 0.022 mmolvitamin C equiv./g-stem, respectively.