Processing of rice husk autohydrolysis liquors for obtaining food ingredients

Rice husks are of a lignocellulosic nature, with a hemicellulose fraction made up of substituted arabinoxylan. Rice husks were treated with hot, compressed water (autohydrolysis reaction) under optimized conditions to cause the hydrolytic degradation of arabinoxylan. The reaction products contained volatile components and nonvolatile components (NVC), which were made up of hemicellulose-derived products (substituted oligosaccharides and monosaccharides) and other nonvolatile solutes (ONVS). To decrease the content of ONVS, concentrated autohydrolysis liquors were first subjected to ethyl acetate extraction and then subjected to various alternative treatments (solvent precipitation, freeze-drying solvent extraction, or ion exchange). The resulting liquors were assayed for composition and yield determination. Material balances are presented for the several processes considered. The best results in terms of purification were obtained with sequential stages of ethyl acetate extraction and ion exchange, which led to concentrates with hemicellulose-derived compounds (sugars and substituted sugar oligomers) accounting for 92 wt % of the NVCs.