Characterization of Hemicellulose B from Corn Fiber by High-Performance Size Exclusion Chromatography with On-Line Molar Mass and Viscometric Detection

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Abstract
Hemicellulose B (arabinoxylan, corn fiber gum, CFG) was prepared from corn fiber (CF) by alkaline extraction with 2 meq/g of CF using either NaOH, Ca(OH)2 or an equimolar mixture of the two. Prior to CFG extraction, oil was removed from CF by extraction with hexane and starch was removed from CF by treatment with α-amylase. The solutions of alkali-extracted CFG were then bleached with alkaline H2O2. The effect of extractant composition on the weight-average molar mass M w, weight-average intrinsic viscosity [η]w, and z-average root-mean-square radius of gyration R gz on CFG was determined. Depending on extractant composition and method of calculation, M w ranged from 2.7–6.96 × 105, [η]w from 1.87 to 2.00 dL/g and R gz from about 31 to 50 nm. Substituting Ca(OH)2 for NaOH reduced M w and R gz but had little or no effect on [η]w. Chromatographic analysis in conjunction with molar mass detection revealed that molar mass distributions were bimodal. M w for the high-molar-mass component ranged from about 8.4–16.1 × 105, whereas M w ranged from about 1.1–2.1 × 105 for the low-molar-mass component. The high-molar-mass component comprised about 15–43% by weight of CFG and was much more compact in shape than the low-molar-mass component.