Changes in flour lipids during the storage of wheat flour.

Abstract

AbstractHigh‐ and low‐grade spring and winter wheat flours of ∼13% moisture were stored at 15, 25 and 37 °C and the lipids were then extracted with water‐saturated n‐butanol.In the original (control) flours there were more neutral lipids and glycolipids in low‐grade winter than in high‐grade winter and in low‐grade spring than in high‐grade spring flours, but there were no corresponding differences in the amounts of phospholipids.The total extractable lipid contents of the flours remained constant in the samples stored at 15 °C, but there were slight losses in the samples stored at 25 and 37 °C. Total lipid contents determined by acid hydrolysis remained constant in all cases indicating that no loss of fatty acids had occurred on storage.There was sufficient hydrolysis of all glycerides to account for the increased amounts of free fatty acids in the stored flours. Some complete deacylation of lipids to free fatty acids and water‐soluble products was indicated. The fatty acid composition of all lipids remained constant, and there was no evidence of any lipoxygenase or other enzymic degradation of fatty acids.Stereoanalysis of the principal glycerides indicated that phosphatidylcholine (and probably also phosphatidylethanolamine) was specifically hydrolysed at the 2‐position, presumably by phospholipase‐A2. Hydrolysis of triglycerides, diglycerides and monoglycerides was attributed to the action of wheat and microbial lipases of unknown specificity. Stereoanalysis of N‐acylphosphatidylethanolamine and the galactosyldiglycerides was not attempted, but it was deduced that they were randomly hydrolysed at the 1‐ and 2‐positions. The changes found in the flour lipids differed from those reported to occur in germinating wheat and in stored damp wheat flour which had been damaged by moulds.