Effects of thermal and mechanical treatments on the physicochemical properties of wheat flour

Planetary ball milling is a possible way to improve the technological properties of wheat flour by thermal and mechanical modifications. In the present study, roller milled common wheat flours (Triticum aestivum L.) were additionally modified in a ball mill by varying mill parameters such as rotation speed and grinding time. As a result of ball milling, the flours experienced temperatures of up to 100 A degrees C, the range of particle sizes strongly increased as well as the content of damaged starch. The treated flours were also analyzed for the protein distribution by SDS-polyacrylamide-gel electrophoresis and proteins were quantitated by an extraction/high-performance liquid chromatography (Osborne fractionation) and an extraction/gel permeation chromatography procedure (SDSL/GMP fractionation). Intense mechanical/thermal treatment led to a decrease of the content of extractable protein and shifted ethanol-soluble gliadins to the glutenin fraction. Cysteine-containing alpha- and gamma-gliadins initially soluble in 60% ethanol were bound to ethanol-insoluble glutenins by thiol-disulfide interchange reactions. Linked to that, a high level of modification also significantly decreased the gliadin/glutenin ratio and increased the glutenin macropolymer content. Cysteine-free omega5- and omega1,2-gliadin types were only weakly affected by milling. Heating induced by mechanical treatment is supposed to be mainly responsible for these effects. Thiol-disulfide interchange can also explain the increase of the particle size after intense ball milling, because flour particles could stick together via disulfide bonds between proteins located on the surface of different particles.