Effect on baking quality of changes in lipid composition during wholemeal storage

Abstract

A simple and relatively rapid method for measuring the lipase activity of wholemeal flour has been developed. It involves measurement of the increase in fatty acid content observed during incubation of unhydrated wholemeal at elevated temperatures. The lipase activities of different samples of finely-milled wholemeal showed a high correlation with their known rates of deterioration (as measured by rates of O 2 -uptake over a period of 20 weeks storage under ambient conditions). There appeared to be a close association between lipase activity and loss of baking performance during storage of wholemeal, with high lipase activity being associated with poor baking performance. Storage of wholemeal at +20 °C for 23 weeks had a deleterious effect on baking quality (as measured by loaf volume and crumb texture). Addition of pure oleic and linoleic acids to freshly-milled wholemeal in amounts typically found in storage-deteriorated flour were equally detrimental to loaf volume; palmitic acid added at the same concentration had no effect. The effects of the fatty acids on baking quality were related to their ability to ‘bind’ to non-lipid components during dough mixing. Restoration of the triacylglycerol content in stored wholemeal (23 weeks at +20 °C) to that found in the freshly-milled flour improved the baking performance of the stored wholemeal; however, addition of the same amount of triacylglycerol also improved the baking performance of freshly-milled wholemeal. Interchanging the lipids between freshly-milled and stored wholemeals showed that the extracted lipid fraction from the stored wholemeal could account totally for the decreases in baking quality observed when using stored wholemeal flour.