Analysis of the Differences in the Composition and Properties of Crude and Refined Wheat Starches from the Front, Middle and Back Flour Mill Streams

Crude starches (C-S-1, C-S-2, C-S-3 and C-S-4) were prepared the dough method from wheat flours with different processing degrees from the wheat processing line, the front (S-1), middle (S-2 and S-3) and back (S-4) flour mill streams, and refined starches (R-S-1, R-S-2, R-S-3 and R-S-4) were obtained after the removal of yellow waste slurry. The effects of the retention or removal of yellow waste slurry on physicochemical indexes, pasting properties, gelatinization properties, granular morphology and crystal structure of wheat starch were investigated. It was shown that the particle size of the crude starches was larger than that of their refined counterparts (D₁₀ 7.51–8.26 μm versus 6.46–7.70 μm). High contents of impurities, specifically ash, crude protein and pentosan, were found in the crude starches than their refined counterparts. X-ray diffraction analysis showed that both crude and refined starches had an A-type crystalline structure, and the relative crystallinity of the latter was higher than that of the former. Their paste properties were significantly different. The refined starches had higher transparency, peak viscosity, final viscosity and trough viscosity but lower solubility and swelling strength than the crude starches. There was no significant difference in textural properties between the crude and refined starch gels, except that the hardness and gel strength of the back-stream starch were higher than those of the front- and middle-stream starches.