Author:

Keywords:

Wheat flour lipids, Lipases, Gas cell stability, Dough liquor, Dough uniaxial extension

Abstract:

While lipids occur in wheat flour in only low levels (2-3%), they tremendously affect bread loaf volume (LV) and crumb structure. Lipases are lipid degrading enzymes. They are excellent research tools and potential alternatives for certain additives in bread making. Although the impacts of different wheat flour lipids on LV and crumb structure are quite well established, knowledge on the functional effects of their enzymatically released hydrolysis products in bread making is scarce. Likewise, the mechanisms underlying the impact of lipids on bread quality remain largely unclear. In this context, we investigated the role of wheat endogenous lipids and their enzymatically released hydrolysis products in bread making. Hereto, lipases were used as research tools in bread making with different wheat flours. Two lipases for commercial bread making, one for degumming edible oils and one used in detergent compositions were applied. Conventional bread making flour as well as flour from soft wheat cultivar Alpowa and three hard near-isogenic wheat lines derived thereof were used. Dough and bread were prepared according to a straight-dough method. Dough liquor (DL), a fraction considered to be representative for liquid films surrounding gas cells in dough, was obtained by ultracentrifugation. The impact of lipids on bread quality was studied by relating lipase-induced changes in the dough lipid population to those in bread LV. Conversion of endogenous lipids into their corresponding lysolipids increased LV. In spite of being minor flour constituents, lipids are thus excellent targets for improving bread quality. This positive effect of lipases was however restricted by the unavoidable accompanying release of detrimental free fatty acids. An appropriate balance between different types of lipids is thus crucial in bread making. We were able to propose in detail which reactions are preferably catalysed by a bread making lipase. Our findings are of use in the development of new lipases and wheat varieties for bread making. Our experimental setup allowed to propose a mechanism whereby lipids impact bread quality. It entirely relies on the ability of lipids to directly stabilize gas cells in dough by aligning at gas/liquid interfaces. Although this mechanism is in line with recent views of other researchers, its validity could not be proven by relating lipase-induced changes in DL composition and properties to such changes in LV. An indirect impact on gas cell stability of lipids was demonstrated by evaluating the effect of lipase on dough rheology with an uniaxial dough extension test. Including lipase in the recipe significantly increased dough extensional viscosity. Altogether, we speculate that the impact of lipids on bread LV results from both their indirect and direct effect on gas cell stability. Our findings contribute to a unified theory on the role of lipids in bread making.