Nitrogen topdressing timing influences the spatial distribution patterns of protein components and quality traits of flours from different pearling fractions of wheat (Triticum aestivum L.) grains

The major components determining wheat flour quality such as protein and protein fractions are unevenly distributed in different fractions of grains, which result in the spatial variations in processing quality of the corresponding flours. In this study, wheat grains were pearled into nine fractions from the outermost to the innermost layers. The effect of nitrogen topdressing timing basing on leaf age on the spatial distribution of bread-baking quality and contents of proteins within flour from different layers of grains in two wheat cultivars were analyzed. The contents of gliadin, glutenin and gluten presented a unimodel curve and peaked at the 2nd (P2) or the 3rd (P3) layer from the outmost of grains. Baking quality was the best with the breads made of flour from the P3 and P4 fractions. Delaying application of topdressed nitrogen increased contents of gluten proteins in each fraction, especially for layers of the aleurone and the outer endosperm. In addition, topdressing at the emergence of the topmost leaf of the main stem (the flag leaf, TL1) resulted in the highest bread-baking quality traits of volume, sensory score and texture profile analysis indexes with flour from each pearling fraction. The results indicated that better bread-baking quality could be achieved by selecting flour from the optimal pearling fractions of grains, and by delaying application of topdressed nitrogen.