Cereal Chem. 75(5):595-601In control dough, endogenous wheat lipase was inactive, because the triacylglycerol (TAG), 1,2-diacylglycerol (DAG 1,2 ), and 1,3-diacylglycerol (DAG 1,3 ) fractions of nonpolar lipids were not affected by mixing. Conversely, the free fatty acid (FFA) and monoacylglycerol (MAG) fractions decreased, mainly due to the oxidation of polyunsaturated fatty acids (PUFA) catalyzed by wheat lipoxygenase. Addition of exogenous lipase to flour (15 lipase units [LU] per gram of dry matter) resulted 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 DAG 1,3 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 released by lipase activity was oxidized by wheat lipoxygenase, resulting in major losses of PUFA. Conversely, the net content of the saturated and monounsaturated fatty acids (SMUFA) remained constant, because the free SMUFA content increased primarily at the expense of the esterified forms. For a constant mixing time of 20 min, increasing the amount of lipase added to dough (from 2.5 to 25 LU/g of dry matter) resulted in a linear decrease in the TAG fraction and a linear increase in the SMUFA content in the FFA fraction. At the same time, the PUFA content of 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.

The lipid profiles of wheat flour doughs containing exogenous lipase were studied under different mixing conditions using a microscale mixer. An experimental design comparing the effects of dough water content (52–68%), the speed of mixing (50–100 rpm), and the mixer temperature (18–32°C) showed that the hydrolysis levels were positively influenced by temperature and speed of mixing and negatively influenced by water content. The positive effect of temperature was enhanced both by highspeed mixing and low water content. The lipid oxidation levels were positively influenced by the speed of mixing and negatively influenced by the water content. The positive effect of temperature on the oxidation levels was less important. A series of experiments conducted with different types of industrial and semi‐industrial mixers with equal concentrations of lipase added to the dough showed large differences among the rates of lipid hydrolysis and oxidation. However, the mixing conditions proposed by bakers to obtain doughs with similar handling properties led to similar dough lipid profiles. Sodium chloride did not change the lipid profile when added to dough. Conversely, calcium chloride promoted a large increase of lipid hydrolysis and oxidation due to its activation of lipase activity. Addition of yeast increased the lipid hydrolysis and slightly decreased lipid oxidation.

Effects of glucose oxidase or lipase addition on dough consistency and oxygen consumption during mixing of unyeasted flour dough.Addition of glucose oxidase enhances dough oxygen consumption and promotes transient peaks of consistency. The delay of apparition of these peaks is shortened with increasing amounts of glucose oxidase added, with the amount of glucose added and with the peroxidase activity. Conversely, the delay of apparition of these peaks increases with increasing amounts of free ferulic acid added to the flour and when catalase activity is added to the dough. Results are discussed by hypothesizing that the glucose oxidase activity in the dough produces hydrogen peroxide and enhances peroxidase activity. This latter enzyme would catalyse macromolecular cross-linking by phenolic linkages. Addition of exogenous lipase promotes both dough consistency and dough oxygen consumption during mixing. Results are in agreement with the fact that lipase activity in the dough increases the polyunsaturated free fatty acid concentration, enhancing the flour endogenous lipoxygenase activity.

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