Extraction of dietary fiber from Citrus junos peel with subcritical water

a b s t r a c t The juice processing by-product of Citrus junos is a high potential source of valuable compounds such as essential oils and a high amount of dietary fiber, consisting of pectin, hemicellulose, and cellulose. The residues obtained from supercritical CO2 extraction of C. junos peel was used as a starting material for hydrothermal treatment to separate pectin and hemicellulose. The experimental apparatus used was a semi-continuous flow extractor. Treatment conditions were in the temperature range of 160–320 ◦ C and water flow rates of 2.1, 3.5, and 7.0 mL/min under a pressure of 20 MPa. Approximately 78% of the pectin was contained in the fraction collected at 160 ◦ C at each flow rate. Most of the hemicellulose was separated from cellulose up until the fraction obtained at 200 ◦ C. The proportion of cellulose in the residue obtained after hydrothermal treatment at 200 ◦ C reached about 80%. Moreover, the characteristics of recovered cellulose were expected to exhibit greater crystallinity and lower impurity than that of the raw material based on the results of scanning electron microscopy (SEM), attenuated total reflectance Fourier transmission infrared (ATR-FTIR), and thermogravimetric-differential thermal analyses (TG-DTA).