Optimisation of the Selective Extraction of (Glucurono)arabinoxylans from Wheat Bran: Use of Barium and Calcium Hydroxide Solution at Elevated Temperatures

Two approaches were investigated in attempts to obtain a high extraction yield of (glucurono) arabinoxylans from water-unextractable cell wall material (WUS) of wheat bran using saturated barium hydroxide containing 0·26 M sodium borohydride. First, the effect of three pretreatments (autoclave treatment, alkaline peroxide and chlorite delignification) of the WUS prior to extraction appeared to have no effect on the extraction yield. Moreover, modifications to the composition and molecular weight distribution of the (glucurono)arabinoxylans occurred when such treatments were used. Second, the effect of an increasing extraction temperature and concentration of alkali was investigated. Increasing the extraction temperature improved the extraction yield of (glucurono)arabinoxylans from 29% at 20°C to 50% at 95°C. Increasing the barium hydroxide concentration with the temperature resulted in no further improvements in extraction yield up to 70°C. Above this temperature the extraction yield decreased. Substitution of barium hydroxide by calcium hydroxide resulted in lower yields and a lower selectivity; the lower solubility of calcium hydroxide may have been responsible for this. Supplementary experiments to investigate the mechanism of the selectivity of the bivalent hydroxide extraction with addition of sodium borohydride indicated a possible role for borate, derived from borohydride.