A commercial GH 11 xylanase mediates xylan solubilisation and degradation in wheat, rye and barley as demonstrated by microscopy techniques and wet chemistry methods

Xylanases in animal feed are primarily utilized to alleviate the antinutritional effects of arabinoxylan, a predominant polymer in cereal cell walls consisting of a beta-1,4-xylose polymer, substituted with various sugars. Although xylanases efficiently hydrolyze unsubstituted and substituted arabinoxylans, currently available enzymes are not always able to access highly decorated forms of the polysaccharide, such as arabinoxylans (AX) that contain arabinofuranose substitutions. The highly substituted regions are enriched in both 2- and 3-disubstituted xylose residues. Wheat AX contains very small amounts of 2-monosubstituted xylose residues, whereas barley AXs are characterised by a larger amount of 2-monosubstitution. The structure of rye AX is similar to that of wheat AX, but differences in the abundances of the 2- monosubstituted and 2-and 3-disubstituted xylose residues have been reported. In the current study the efficiency of a monocomponent xylanase was demonstrated on structurally different arabinoxylans present in wheat, rye and barley kernels using microscopic visualization, viscosity and arabinoxylan solubilisation measured as the sum of arabinose and xylose in an analysis of the non-starch polysaccharide (NSP) constituents, as well as xylose alone. Degradation of arabinoxylan components upon exposure to the enzyme was visualized by scanning electron microscopy, autofluorescence and with fluorescence immunocytochemistry and confocal microscopy using commercial antibodies recognizing arabinoxylan in the cereal cell walls. Viscosity data clearly demonstrated effective depolymerisation of arabinoxylans in water extracts from wheat and rye and thereby hydrolytic capacity of the mono component enzyme on structurally diverse arabinoxylans. The viscosity reducing effect observed in barley was limited, most likely due to the presence of highly viscous mixed linked beta-D-glucans. Wet chemistry analyses of the complete solubilisation of arabinoxylan (oligomers and polysaccharides) using a standardized xylose assay as well as NSP analyses (measuring polysaccharides, DP >10) on wheat, rye and barley, provided additional and complementary information to the microscopy conducted on the same cereal samples. The study has shown that microscopy techniques visualizing cell wall solubilising effects of xylanase can be useful for understanding enzyme mode of action and efficacy on different feed ingredients. (C) 2016 Elsevier B.V. All rights reserved.