Properties of Rice Stem Extracts Obtained by Subcritical Water/Ethanol Treatment

Rice straw stem was treated with subcritical water, ethanol, or a mixture at 170 degrees C to 230 degrees 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 degrees C. The extract obtained using 75% (v/v) ethanol at 230 degrees 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 mmol-vitamin C equiv./g-stem, respectively.