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Comparison of solvent extraction methods for analysis of wheat flour lipids and how lipid classes are changed by aging
N. B. GHAHNAVIEHEI (1). (1) University of Nottingham, Leicestershire, United Kingdom

Lipids are minor components of flours, but are major determinants of baking properties and end-product quality. Therefore, the accurate determination of lipids is essential for the full explanation of the functional properties of flours. Nine solvent systems were compared for their ability to extract non-starch lipids from wheat flour (by lipid classes). The solvent systems that extracted the most non-starch lipids from wheat flour were Bligh and Dyer and a modified Bligh and Dyer (with HCl), whereas Bligh and Dyer modified using HCl improved the recovery of phospholipids. The functionality and lipid profile of aged flour (42 days at 30ºC) was compared to control samples (-20ºC). During ageing the total lipid content of flour sample reduced by 14.6%; this reduction in lipids was different for different lipid classes with a 27.3% reduction for non-polar lipids, a 37.4% reduction for glycolipids and a 20.3 % reduction for phospholipids. In addition, there was a 48.3% increase in free fatty acids. The reduction was driven by unsaturated fatty acids in the neutral and glycolipids fractions. From a functionality perspective the addition of Diacetyl Tartaric (Acid) Ester of Monoglyceride (DATEM) had no impact on the control flour but showed a significant enhancement in the functionality of the aged flour. It is believed that the control flour was already at the limits of performance and the changes occurring during ageing are driven partially by modifications in the lipid components, principally the glycolipid fraction, due to its surface active contribution in bread making. Aging caused an increase in water absorption and a decrease in the degree of softening; this could be due to the loss of lipids that can coat starch granules and the gluten proteins. There was also a shortening effect, where the dough became stronger but less elastic i.e. tighter.

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