effect of lipoxygenase action on the mechanical development of doughs from fat extracted and reconstituted wheat flours

The mechanism by which soya lipoxygenase enzyme action improves the Theological properties of wheat flour doughs during mechanical development in air has been investigated further. Free‐lipid extraction, reconstitution and replacement experiments have shown that the rheological effect of lipoxygenase action, which is consistent with an oxidative improvement of the dough proteins and may also result in extended mixing tolerance, only occurred in the presence of an oxidisable, polyunsaturated, free‐lipid substrate. Addition of this substrate in an oxidised state (produced either by autoxidation or enzyme‐oxidation) to doughs mixed from fat‐extracted flour under nitrogen resulted only in a small rheological improvement, greater for the autoxidised than the enzyme‐oxidised lipid, but in no way comparable with the large rheological effect of lipoxygenase action during dough mixing in air. Furthermore, the presence of an antioxidant, nordihydroguaiaretic acid (NDGA), during dough development, although greatly inhibiting peroxide formation, only marginally impaired the rheological improvement due to lipoxygenase action. Additional evidence is therefore provided for a coupled oxidation mechanism being responsible for the rheological effect, since lipoxygenase‐catalysed oxidation actively occurring in the dough during mixing appears to be the fundamental requirement, irrespective of whether the primary oxidation products lead to lipid peroxides or oxidised NDGA.