Involvement of Non-Starch Lipids from Endogenous Wheat in the Development of Bread Dough Rancidity During Frozen Storage

The involvement of free and bound lipids on the development of rancidity in wheat-bread dough is studied following frozen storage for 24 months. Lipid oxidation and oxidative stability are determined by assaying peroxide value and thiobarbituric acid reactive substances, which indicate that lipid oxidation starts after three months. High performance liquid chromatography and gas chromatography are used to characterize changes in lipid profile and fatty acid composition, respectively. The bound lipid fraction is mainly composed of polar glycolipids and phospholipids, and their content decreases with storage time because the unsaturated fatty acids in the bound lipid fraction are oxidized. It appears that endogenous wheat lipids, especially the polar lipids with amphiphilic structures and surface activity are most exposed to oxygen because they accumulate at the interface around, and stabilize, the gas cells in the foam structure of the bread. Practical Applications: This study has demonstrated that polar lipids, such as galactolipids, are the most susceptible to oxidation, apparently because they are enriched at the gas bubble interface, where they improve gas bubble stability, but they are also in close contact with oxygen in the gas bubbles. An important practical finding from this study is that lipid oxidation was negligible in the first 3 months of frozen storage (-10 degrees C) and only became extensive after 6 months. This is important information for the baking industry.