OPTIMIZATION 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 extracti on yield of (glucurono) arabinoxylans from water-unextractable cell wa ll material (WUS) of wheat bran using saturated barium hydroxide conta ining 0.26 M sodium borohydride. First, tie effect of three pretreatme nts (autoclave treatment, alkaline peroxide and chlorite delignificati on) of the WUS prior to extraction appeared to have no effect on the e xtraction yield. Moreover, modifications to the composition and molecu lar weight distribution of the (glucurono)arabinoxylans occurred when such treatments were used. Second, the effect of an increasing extract ion temperature and concentration of alkali Tvas investigated. Increas ing the extraction temperature improved the extraction yield of (glucu rono)arabinoxylans from 29% at 20 degrees C to 50% at 95 degrees. Incr easing the barium hydroxide concentration with the temperature resulte d in no further improvements in extraction yield up to 70 degrees C. A bove this temperature the extraction yield decreased. Substitution of barium hydroxide by calcium hydroxide resulted in lower yields and a l ower selectivity; the lower solubility of calcium hydroxide may have b een responsible for this. Supplementary experiments to investigate the mechanism of the selectivity of the bivalent hydroxide extraction wit h addition of sodium borohydride indicated a possible role for berate, derived from borohydride. (C) 1996 Academic Press Limited