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Physicochemical Properties of Wheat Fractionated by Wheat Kernel Thickness and Separated by Kernel Specific Density

¹Dept. Biosystems Engineering, Zhejiang University, Hangzhou 310029, China. ²Corresponding author. E-mail: jwang@zju.edu.cn ³Zhejiang Province Hangzhou Dongnan flour Co., Hangzhou 310014, China. ⁴Dept. Food Science, Beijing Agricultural Institute, Changping District, Beijing 102206, China. ⁵College of Engineering, Nanjing Agricultural University, Pukou district, Nanjing 210031, China.

Two wheat cultivars, soft white winter wheat Yang-mai 11 and hard white winter wheat Zheng-mai 9023, were fractionated by kernel thickness into five sections; the fractionated wheat grains in the 2.7–3.0 mm section were separated sequentially into three fractions according to kernel specific density. Physical properties of unfractionated, fractionated, and separated wheat grains and the physicochemical properties of processed wheat flour were determined. Test weight, relative density, and whiteness of flour in the middle kernel thicknesses were maximal and those properties decreased with increasing or decreasing kernel thickness; they also decreased with decreasing kernel specific density. Extensigraph properties showed the same results. Water absorption of flour and kernel hardness increased with increasing kernel thickness and decreasing kernel specific density. The farinograph properties also were related to kernel thickness and specific density. Pasting viscosity increased with increasing kernel thickness for sections from <2.5 mm to 3.0–3.2 mm, except that the >3.2 mm section was lowest; the kernels with the lightest specific density also were lowest. Thus, the quality of wheat grains with the greatest kernel thickness was not the best, and in fact may be the worst. The quality of wheat grains with small kernel thickness and light kernel specific density generally were worst. Most physicochemical properties of unfractionated and unseparated wheat grains were accurately predicted by the weighted-average of the different kernel thickness sections and different kernel specific density fractions, except relative density, falling number, dough development time, and pasting temperature.