Enzymic Degradability of Hull-less Barley Flour Alkali-Solubilized Arabinoxylan Fractions by Endoxylanases

• Published in: Journal of agricultural and food chemistry Vol. 53; no. 18; pp. 7243 - 7250
• Main Authors: Trogh, Isabel, Croes, Evi, Courtin, Christophe M, Delcour, Jan A
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 07-09-2005
• Subjects: arabinose; arabinoxylan; Aspergillus - enzymology; Aspergillus aculeatus; Bacillus subtilis; Bacillus subtilis - enzymology; barley; Biological and medical sciences; carbohydrate composition; Chemical Fractionation; Endo-1,4-beta Xylanases - metabolism; endo-1,4-beta-xylanase; enzymatic treatment; flour; Flour - analysis; Food industries; Fundamental and applied biological sciences. Psychology; Hordeum - chemistry; hull-less barley flour; Hydrogen-Ion Concentration; molecular weight; Solubility; Substrate Specificity; Xylans - isolation & purification; Xylans - metabolism; xylose; Alkali; endoxylanase; Barley flour; degradability; hull-less barley flour; Polysaccharide; Arabinoxylan
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/jf0506784

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 ∼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. Keywords: Arabinoxylan; endoxylanase; degradability; hull-less barley flour