Changes of chemical composition and dough rheology in two fractions of sieve-classified Polish spring wheat flour

The study of chemical composition and dough rheology changes in sieve-classified two fractions (up to 60 and 60-240 microm particles) of wheat flour was the subject of this study. The straight grade flours were obtained by the milling of three Polish varieties of spring wheat, differing in particle size index (PSI) values. The flours were separated with the use of an SZ-1 laboratory sifter. The yield of fine fraction was in the range 50.0-55.7%. The obtained fractions were assayed for the content and composition of free lipids, gluten proteins, damaged starch, ash, water absorption and amylograph viscosity. Dough rheology (extrusion in OTMS cell, alveograph and farinograph tests) and baking trials were also performed. The content of free lipids, including the non-polar and phospholipids was lower and the content of glycolipids was higher in fine flours. Those fractions were more rich in linoleic acid but the lower content of oleic and linolenic acids resulted in a higher oxidizability index of free lipids. Fine flours contained less ash and significantly more damaged starch. At the same time, they were characterized by a higher content of wet gluten, water absorption, amylograph viscosity and better dough parameters. This was reflected in the bread volume, which was higher by 6.3-10.7%. The influence of the changes in composition and the content of free lipids upon the rheology of the dough after the 90 days flour storage has not been defined unambiguously and requires further research.