ENZYMATIC DEGRADATION OF WATER-UNEXTRACTABLE CELL-WALL MATERIAL AND ARABINOXYLANS FROM WHEAT-FLOUR

Differences were investigated in the enzymic breakdown of water-unextractable cell wall material (WUS) of wheat flour by endoxylanase I (endoI) and endoxylanase III (endoIII) purified from Aspergillus awamori. The degradation by these enzymes of water-extracted alkali-extracted arabinoxylans was also examined. Both enzymes released in total 90% of the arabinoxylans present in the WUS, without solubilization of glucomannans, (1→3, 1→4)-β-glucans and cellulose. Both poly- and oligosaccharides were released during the incubation. Arabinoxylans with similar arabinose/xylose ratios, obtained from different fractions of the WUS, showed different degrees of degradation. No differences could be observed in enzymic solubilization and degradation between WUS and alkali-extracted arabinoxylans from different wheat cultivars. Compared with endoI, incubation with endoIII resulted in a more rapid solubilization and/or degradation of WUS and extracted arabinoxylans. EndoIII digestion resulted also in a more rapid decreased in the total water-holding capacity of the residual WUS, although, when the water-holding capacity was expressed on a per gram of residual WUS basis, a two-fold increase was observed as result of enzyme incubation. Application of endoIII in baking trials yielded a 14% increase in loaf volume, together with an improvement in crumb structure and 'break and shred', whereas endoI yielded only a 4% increases of loaf volume with no improvement of other baking characteristics. © 1993 Academic Press Limited.