Separation of bread wheat flours into starch and gluten fractions: effect of water temperature alone or in combination with water to flour ratio

Abstract

Two different commercial bread wheat¯ours (BF-I, 65% extraction and BF-V, 86% extraction) were separated into gluten and starch milk by making a dough, allowing some time for maturation, dispersing the dough in water and wet sieving/washing. The effect of using of warm water (20±45°C) for dough making and washing on separation was studied for BF-I¯our at 640 g kg À1 water tō our ratio of and 300 s maturation time, and the separation was found to improve with increase in temperature. The combined effects of water temperature (20±50°C) and water to¯our ratio (640± 780 g kg À1 for BF-I and 620±870 g kg À1 for BF-V) were studied at 600 s maturation time. The quantities and dry matter contents of the gluten fraction and starch milk were measured; a sample of starch milk was centrifuged to obtain decantate, tailing and prime starch fractions, and the dry matter contents of each were determined. All the dried samples were also analysed for protein content, and the fractional recoveries of dry matter and protein in the gluten fraction, prime starch, tailings and decantate were calculated. The results indicated the optimum point for BF-I¯our to be the combination of optimum farinograph water absorption and 40°C. BF-V showed very poor separation behaviour within the ranges studied. At the optimum farinograph water absorption the use of warm water for dough making and 20°C water for washing steps was also tried, but no signi®cant improvement over the 20°C results was obtained. INTRODUCTIONThe manufacture of wheat starch and gluten is generally carried out by the wet separation of wheat our into fractions. The temperature of the process water, however, is not even mentioned in some literature reports about this process, indicating the use of water at the temperature it is available. Anderson et al. 1 reports the use of 48±57°C water for initial mixing in the batter process`to facilitate hydration of gluten and to reduce the mixing time necessary for producing a batter of proper consistency', but the use of`cold' water for the washing process. He found protein concentrations of 1.9±2.4% (dry basis, db) in starch milk for various whole wheat ours and 2.8 and 4.4% (db) protein in starch milk of ®rst and second clear¯ours. Knight 2 mentions an unpublished study on the effects of wash water temperature in the range 5±25°C, which indicated the use of water at higher temperatures.Our earlier work 3,4 on the combined effects of water to¯our ratio in dough making and maturation time showed that the wet separation behaviour was more strongly affected by the water to¯our ratio. Use of the optimum water to¯our ratio obtained by farinograph