Isolation and structural analysis of hemicellulose from corncobs after a delignification pretreatment
Corncobs are rich in hemicellulose, which has very important applications in the food industry and biofuels. In this study, hemicellulose was extracted from corncobs after a delignification pretreatment using a three-step extraction. The yield of hemicellulose was nearly 77.64% of the total available hemicellulosic polysaccharides in the pretreated corncobs. Three corresponding fractions HW, HA and HE were obtained, and they all exhibited narrow polydispersity. The amount of HA extracted by alkali accounted for 86.86% of the total amount of the isolated hemicellulose. Its average molecular mass was 24322 g mol−1, which was much higher than that of HW (2497 g mol−1) and HE (2680 g mol−1). HW had a higher thermal stability than the other two fractions and structural analysis indicated that the main structures of these three fractions were slightly different. Nuclear magnetic resonance indicated that fraction HA was mainly composed of 4-O-methyl-α-D-glucurono-α-L-arabino-β-D-xylan. Structural characterization of the hemicelluloses extracted using the three extraction steps will provide information for their further applications in food, pharmaceuticals and other industrial fields.