The role of wheat (Triticum aestivum L.) endogenous lipids in bread making and bread quality

The four essential ingredients in wheat (Triticum aestivum L.) bread making are flour, water, yeast, and salt. Wheat flour typically makes up more than half of the recipe. Its characteristics and functionality, hence, determine bread quality. Its main constituents are starch, water and protein. Flour also contains low levels of non-starch polysaccharides and lipids. Wheat lipids form a complex group of components with varying polarities. They occur as starch internal lipids or as non-starch lipids, with the latter being analysed as either free or bound based on their extractabilities with solvents of opposing polarities. Despite their low levels in wheat flour, wheat endogenous lipids exert a profound role in bread making and product quality. Several hypotheses have been proposed with regard to their action mechanisms during bread making. These include (i) indirect stabilization of gas cells by strengthening the gluten network, (ii) direct stabilization of gas cells by lipids positioning themselves at gas cell interfaces or (iii) a combination of both. However, the methodologies applied to date do not allow to either confirm or reject these hypotheses. Therefore, in this doctoral work, a lipase-based approach was applied to further elaborate on the role of wheat endogenous lipids in the entire bread making process and to understand how they affect bread quality and its evolution over time. Lipases can in situ selectively modify the lipid population without altering other flour constituents. In a first part of this doctoral work, a method to extract, separate and detect endogenous wheat lipids in a single chromatographic run was optimized. This method was then applied to study the lipid (re)distribution in the transition from flour to bread. Profiles obtained with a high pressure liquid chromatograph coupled to an evaporative light scattering detector of free and bound lipid extracts of wheat flour, its derived dough (both during development and fermentation), and of bread made thereof were analysed and compared. This revealed that dough mixing redistributed lipid from the free to the bound lipid fraction, which has already long ago been referred to as lipid binding . Surprisingly, major redistribution of lipids occurred already before the gluten network was optimally developed. That more lipids could be extracted in total from dough than from flour, was related to flour particle disintegration and simultaneous release of previously unextractable (polar) li