Changes in wheat lipids during mixing and resting of flour‐water doughs

Lipids extracted with water‐saturated n ‐butanol from flour and flour‐water doughs were examined to determine the extent of oxidations and other changes which occurred in mixing and resting dough. Extracted lipids were converted to fatty acid methyl esters (FAME) and quantified by gas‐liquid chromatography (g.l.c.) using heptadecanoic acid (17 : 0) as internal standard. The original flour or dough and the corresponding solvent‐extracted residues were acid hydrolysed, and the hydrolysate lipids converted to FAME for g.l.c. determination of the total lipid and residual unextracted lipid contents. The total flour or dough lipids equalled the extracted lipids + unextracted lipids, except where there were unavoidable autoxidative losses of linoleate (18 : 2) and linolenate (18 : 3). The unextracted flour lipids (13% of total lipids) were not oxidised during dough mixing. There were no changes in any of the extracted lipid classes other than free fatty acids (FFA) and monoglycerides (MG) which showed losses of 18 : 2 and 18 : 3 after aerobic dough mixing. Losses of FFA and MG are attributed to lipoxygenase activity during dough mixing and the period immediately after. The small amount of 18 : 2 in the “free” petroleum ether‐extracted FFA appeared to be unaffected by lipoxygenase. Recoveries of FFA other than 18 : 2 or 18 : 3 were constant, indicating no lipolysis of glycerolipids and no general oxidation or degradation of FFA. Experiments with [U‐ 14 C]palmitic acid confirmed that there was no oxidation, degradation or re‐esterification of FFA. Much of the non‐polar lipids (steryl ester, triglyceride, diglyceride, FFA, MG) and almost all of the polar lipids were bound on dough mixing. Binding was non‐selective with regard to fatty acid composition. Triglyceride was the only lipid class bound to a greater extent in anaerobic dough than in aerobic dough. Some selectivity of binding between lipid classes was indicated.