Xylan-degrading enzymes and arabinoxylan solubilisation in barley cultivars of differing malting quality

The levels of xylanolytic activities ((1 --> 4)-beta-endoxylanases, beta-D-xylosidases and alpha-L-arabinofuranosidases) and the levels of water extractable arabinoxylans (WEAX) in hot water extracts of malts were compared during malting of four barley cultivars of differing quality. Endoxylanase activity increased from day 1 after steeping showing a slight lag compared with the development of (1 --> 3,1 --> 4)-beta-glucanase activity. The levels of endoxylanase activity were different between the cultivars. For example, at day 4, which would be a suitable endpoint for malting of good quality cultivars, total endoxylanase activities of Static and Chariot malts were twice that of Hart and Optic. This variation in level of endoxylanase between cultivars did not correlate with the content of water extractable arabinoxylans in hot water extracts of the malts. However, those cultivars that accumulated most water extractable arabinoxylan had a different set of endoxylanase isoforms. This suggests that expression of specific endoxylanase isoforms may influence the extent of arabinoxylan solubilisation and/or degradation. The beta-xylosidases and alpha-arabinosidases increased from low levels after steep to a plateau of activity at day 6 or 7 of germination. Total xylosidase was always higher than the arabinosidase activity. There were differences between cultivars but these were small compared with the variation in endoxylanase activity. (1 --> 4)-beta-D-Endomannanase activity was detected in all four cultivars at 2 days germination then rose to a maximum around 5 days. Crown Copyright (C) 2004 Published by Elsevier Ltd. All rights reserved.