Lipid Binding in Worked Wheat Flour Doughs

Abstract

A study has been made of factors affecting lipid binding in wheat flour doughs. Simple flour water doughs, wetted by a method which avoided the introduction of mechanical work, were used to follow changes in lipid binding during the initial stages of dough mixing. Varying the moisture content of such doughs showed that there was a “critical” moisture content below which mechanical work did not cause any appreciable increase in lipid binding. Above this moisture content there was a very rapid binding of flour lipids in the early stages of dough mixing, the total amount of lipid bound increasing as the mixing speed was raised. It was concluded that gluten development was the major factor affecting lipid binding. When fully hydrated doughs containing lipoxygenase-active soya flour were mixed in air this initial rapid increase in bound lipid was followed by a release of bound lipid. The onset of lipid release was shown to occur after the same mixing time irrespective of mixing speed. However the time taken was dependent upon the availability of oxygen in the system. To examine these effects in greater detail the binding of glyceryl tri (oleate-9,10°H), glyceryl tri (palmitate-1-'4c) and palmitic acid- 1-14C,: has been studied by the use of liquid scintillation counting. The use of these labelled compounds revealed a difference in the behaviour of the free fatty acids compared with the triglycerides. Whereas triolein and tripalmitin showed similar overall binding patterns to the total flour lipids, palmitic acid gradually became less extractable with the solvents used to determine free lipid. Moreover it was shown that in both air and nitrogen there was a very rapid interchange of triolein between the free and bound lipid. A new theory of lipid behaviour in dough has been proposed in which it was suggested that the triglycerides were in dynamic equilibrium between the free and bound states. Mixing in nitrogen was thought to shift the equilibrium towards the bound state whilst mixing in air had the opposite effect. The relevance of these observations to current concepts of the nature of lipid binding in wheat flour doughs has been discussed with particular reference to the effect of lipids on baking performance.