Effects of laccase, xylanase and their combination on the rheological properties of wheat doughs

The effects of Trametes hirsuta laccase alone and in combination with Aspergillus oryzae and Bacillus subtilis xylanases on dough extensibility were studied using the Kieffer test to determine the dough extensibility (Ex) and the resistance to stretching (Rmax). Laccase treatment resulted in dough hardening: the Rmax of dough increased and the Ex at Rmax decreased as a function of dosage (5–50 nkat/g flour). Xylanases softened flour and gluten doughs. Hardening by laccases and softening by xylanases was weaker in gluten doughs. Dough hardening, observed in the laccase treatments, decreased as a function of dough resting time. The softening effect occurred especially at higher laccase dosages (≈50 nkat/g flour). The softening phenomenon was related to the laccase-mediated depolymerization of the cross-linked AX network. In combined laccase and xylanase treatments, the effect of laccase was predominant, especially at low xylanase dosage, but when xylanase was added to flour dough at high concentrations, the hardening effect of laccase on dough was decreased. In combined laccase and xylanase treatments in gluten doughs, similar decreases in laccase-mediated hardening were not seen.