Freshly harvested wheat goes through an aging process between harvest and milling (31). This process, sometimes called "sweating, " is thought to affect the baking quality of flour produced from new crop wheat (31). Changes that occur in freshly harvested wheat can cause variations in the baking quality of milled flour (34). Consequently, bakers must adjust their formulations and production processes in an attempt to correct for these variations. Their attempts generally are unsuccessful, however, because the causes of inconsistencies in quality encountered when baking breads and cakes using flour from new crop wheat have not yet been verified. Changes occurring in both new crop wheat and milled flour should be identified, measured, and understood, so efforts can be made to limit the quality variations that bakers experience (34).Storing freshly harvested wheat (hard and soft) prior to milling is known to improve baking quality of refined flour (31,34,35). Studies also have demonstrated that the baking quality of freshly milled refined wheat flour (hard and soft) improves as the flour ages (5,31,34). Unlike refined flour, the baking quality of whole wheat flour is believed to decrease over time (37).Whole wheat flour contains, in addition to the starchy endosperm, the bran and germ components. Whole wheat milling increases the neutral lipids content of the flour compared to polar lipids because the germ and aleurone layers contain higher percentages of neutral lipids (24). When stored together, the bran and germ have a synergistic effect on lipid stability due to the release by the bran of lipases, which hydrolyze esterified fatty acids into free fatty acids (FFA) (17,18). The germ releases lipoxygenase, which reacts with the FFA and starts the process of oxidative degradation (7,17,18). Because the whole wheat kernel contains more unsaturated fatty acids (≈80%) than does refined flour (≈77%) (23), lipid degradation in whole wheat flour is likely. Thus, changes in lipid composition appear to play a role in reducing the baking quality of whole wheat flour (18).Lipids are present in small amounts in the whole wheat kernel (2.5-3.3%) (4) and refined flour (2.0-2.5%) (28). These endogenous lipids affect flour baking quality through the stabilization (polar lipids and saturated FFA) and destabilization (nonpolar lipids and unsaturated fatty acids) of gas cells in dough. Detrimental changes in the lipid fraction during storage of both refined and whole wheat flours, therefore, could affect bread quality.
Flour Lipids in BakingStudies have shown that polar lipids in flour improve baking quality and reduce crumb firming, whereas neutral lipids negatively affect loaf volume and produce a hard crumb (24,29,30). The addition of nonpolar lipids to flour has been found to decrease loaf volume (13,25). Chung et al. (8) reported that as the nonpolar/polar lipid ratio decreased loaf volume increased for hard red winter (HRW) wheat flour.Glycolipids and phospholipids have both polar and nonpolar characteristics (33). Although t...