Effects of laccase and xylanase on the chemical and rheological properties of oat and wheat doughs.

The effects of Trametes hirsuta laccase and Pentopan Mono BG xylanase and their combination on oat, wheat, and mixed oat-wheat doughs and the corresponding breads were investigated. Laccase treatment decreased the content of water-extractable arabinoxylan (WEAX) in oat dough due to oxidative cross-linking of feruloylated arabinoxylans. Laccase treatment also increased the proportion of water-soluble polysaccharides (WSNSP) apparently due to the beta-glucanase side activity present in the laccase preparation. As a result of the laccase treatment, the firmness of fresh oat bread was increased. Xylanase treatment doubled the content of WEAX in oat dough and slightly increased the amount of WSNSP. Increased stiffness of the dough and firmness of the fresh bread were detected, probably because of the increased WEAX content, which decreased the amount of water available for beta-glucan. The combination of laccase and xylanase produced slight hydrolysis of beta-glucan by the beta-glucanase side activity of laccase and enhanced the availability of AX for xylanase with concomitant reduction of the amount and molar mass of WSNSP. Subsequently, the volume of oat bread was increased. Laccase treatment tightened wheat dough, probably due to cross-linking of WEAX to higher molecular weight. In oat-wheat dough, laccase slightly increased the proportion of WSNSP between medium to low molecular weight and increased the specific volume of the bread. Xylanase increased the contents of WEAX and WSNSP between medium to low molecular weight in oat-wheat dough, which increased the softness of the dough, as well as the specific volume and softness of the bread. The results thus indicate that a combination of laccase and xylanase was beneficial for the textures of both oat and oat-wheat breads.