Effects of repeated treatment on the properties of rice stem extract using subcritical water, ethanol, and their mixture

Rice stem was repeatedly treated 3 times with subcritical water, ethanol, and 75% (v/v) ethanol in different orders at 230 °C for 5 min during each treatment step to extract its constituents. The obtained extracts were subjected to an analysis of their yield, carbohydrate content, phenolic content, radical scavenging ability, color, and UV absorption spectra. The highest total carbohydrate and phenolic contents were obtained by treatment with subcritical water, and with subcritical ethanol after pre-treatment with subcritical water, respectively. However, the extract with the highest radical scavenging ability was obtained by treatment with subcritical 75% (v/v) ethanol as the 1st treatment.