CHEMICAL AND PHYSICO-CHEMICAL CHANGES INDUCED IN WHEAT AND WHEAT PRODUCTS BY ELEVATED TEMPERATURES—I

Abstract

Heat treatments of wheat and wheat products were conducted in an apparatus which made it possible to study independently the influence of time, temperature and moisture content. Straight-grade flour, milled from Western Canadian hard red spring wheat (allowed a limited amount of aging) heat treated for varying times at different temperatures and normal moisture content (13.90%) was used in most of the studies. Baking tests conducted on this flour revealed progressive improvement in baking quality, as determined without bromate, with temperature or time of heating being extended within a certain range. No well defined "region" of improvement was observed. Improvement in baking quality was reflected in a better handling quality of the dough and, in the baked loaf, by a decrease in underfermented characteristics, and by a marked improvement in crumb texture. No significant alteration in loaf volume was observed. Improvement in baking quality induced by heat was not comparable in magnitude to that obtained by the addition of 0.001%, potassium bromate to the baking formula, but induced the same general characteristics in the finished loaf. Baking tests with bromate on heated flour revealed damage to baking quality for all heat treatments. Extension of time or temperature of heating, above the range where improvement was observed, caused pronounced damage to baking quality as determined with or without bromate. The damage caused was reflected in decreased loaf volume, over-fermentation characteristics, and coarse texture. Within the range of damage, the baking quality was found to be approximately a linear function of the temperature for constant time of heating. Heat treatment resulted in a marked decrease in fermentation tolerance. This decrease could not be ascribed to lower diastatic activity, since baking tests after the addition of diastatic malt to the baking formula gave similar results. Increasing the moisture content at which heat treatments were conducted markedly reduced the temperature to which flour could be heated without damage to the baking quality. The safe temperature limit for various moisture contents has been fairly well defined. The limiting moisture content at which damage occurred for a fixed temperature and time of heating was very sharp. Heat treatment of wheats showed somewhat less damage to baking quality of the flour milled therefrom than heat treatment of flour under similar conditions.