Author:

Keywords:

arablnoxylan, endoxyfanase, degradablilty, hull-less barley flour, cell-wall material, different substrate selectivity, water-extractable arabinoxylan, wheat-flour, physicochemical properties, nonstarch polysaccharides, cereal arabinoxylans, degrading enzymes, components, fiber, Science & Technology, Life Sciences & Biomedicine, Physical Sciences, Agriculture, Multidisciplinary, Chemistry, Applied, Food Science & Technology, Agriculture, Chemistry, CELL-WALL MATERIAL, DIFFERENT SUBSTRATE SELECTIVITY, WATER-EXTRACTABLE ARABINOXYLAN, WHEAT-FLOUR, NONSTARCH POLYSACCHARIDES, FIBER, COMPONENTS, PENTOSANS, POLYMERS, GLUCOSE, Aspergillus, Bacillus subtilis, Chemical Fractionation, Endo-1,4-beta Xylanases, Flour, Hordeum, Hydrogen-Ion Concentration, Solubility, Substrate Specificity, Xylans, 03 Chemical Sciences, 07 Agricultural and Veterinary Sciences, 09 Engineering, Food Science, 30 Agricultural, veterinary and food sciences, 34 Chemical sciences, 40 Engineering

Abstract:

The impacts of the arabinose to xylose (A/X) ratio of arabinoxylans (AX) and the endoxylanase substrate specificity on the enzymic degradability of hull-less barley flour AX by endoxylanases were studied by using alkali-solubilized AX (AS-AX) fractions with different A/X ratio, on the one hand, and glycoside hydrolase family 10 and 11 endoxylanases of Aspergillus aculeatus (XAA) and Bacillus subtilis (XBS), respectively, on the other hand. AS-AX were obtained by saturated barium hydroxide treatment of hull-less barley flour water-unextractable AX. Fractionation of AS-AX by stepwise ethanol precipitation resulted in structurally different hull-less barley flour AS-AX fractions. Their A/X ratios increased with increasing ethanol concentration, and this increase in A/X ratio was reflected in their xylose substitution levels. For both XAA and XBS, the enzymic degradability of AX and apparent specific endoxylanase activity decreased with increasing A/X ratio of the AS-AX substrates, implying that both endoxylanases were sterically hindered by arabinose substituents. However, for all AS-AX fractions, hydrolysis end products of lower average degree of polymerization were obtained after incubation with XAA than with XBS, indicating that the former enzyme has a lower substrate specificity toward hull-less barley flour AS-AX than the latter. In addition, apparent specific endoxylanase activities indicated that XBS was similar to 2 times more sensitive to variations in the A/X ratio of AS-AX fractions than XAA. Furthermore, AS-AX with higher A/X ratio were relatively resistant to degradation by XBS.