EFFECT OF EXOGENOUS LIPASE ON DOUGH LIPIDS DURING MIXING OF WHEAT FLOURS

In control dough, endogenous wheat lipase was inactive, because the tr iacylglycerol (TAG), 1,2-diacylglycerol (DAG(1,2)), and 1,3-diacylglyc erol (DAG(1,3)) fractions of nonpolar lipids were not affected by mixi ng. Conversely, the free fatty acid (FFA) and monoacylglycerol (MAG) f ractions decreased, mainly due to the oxidation of polyunsaturated fat ty acids (PUFA) catalyzed by wheat lipoxygenase. Addition of exogenous lipase to flour (15 lipase units [LU] per gram of dry matter) resulte d in substantial modification of nonpolar lipids during dough mixing. Due to the 1,3 specificity of the lipase used in this experiment, the TAG and DAG1,3 fractions decreased, whereas the MAG and FFA fractions increased. The DAG(1,2) fraction increased at the beginning of mixing and decreased after 40 min of mixing. Moreover, part of the PUFA relea sed by lipase activity was oxidized by wheat lipoxygenase, resulting i n major losses of PUFA. Conversely, the net content of the saturated a nd monounsaturated fatty acids (SMUFA) remained constant, because the free SMUFA content increased primarily at the expense of the esterifie d forms. For a constant mixing time of 20 min, increasing the amount o f lipase added to dough (from 2.5 to 25 LU/g of dry matter) resulted i n a linear decrease in the TAG fraction and a linear increase in the S MUFA content in the FFA fraction. At the same time, the PUFA content o f the FFA fraction increased only for additions of lipase to flour of >5 LU/g of dry matter, due to partial oxidation by wheat lipoxygenase.