Role of Wheat Protein Fractions in the Expansion of Yakifu (Baked Gluten Product)

Abstract

The relationship between wheat flour protein and the expansion of yakifu, one of the traditional foods in Japan, was studied. Wheat flour proteins were fractionated by their solubility in various solvents. The protein fraction (PF) and wheat starch were blended into reconstructed flours (RFs). In RF 1, the protein content was equal to that of hard wheat flour, while in RF 2 part (10%, 20%, or 30%) of the protein originally included in soft or hard wheat flour was replaced with a PF extracted from each flour. Among RF 1, those blended with water-soluble and NaCl-soluble fractions did not produce substantial gluten doughs and therefore failed to form well expanded structures when baked. A smooth and well homogenized gluten dough was prepared with 70% ethyl alcohol-soluble and HCl-soluble fractions although the acetic acid-soluble, acetic acid-insoluble, and HCl-insoluble fractions produced a tough and coarse gluten dough. The specific volume of yakifu was greater when smooth and well homogenized gluten doughs were baked than when tough and coarse ones were. In RF 2, the specific volume gradually increased with the increase of the HCl-soluble fraction ratio, while it remained almost constant with the increase of the HCl-insoluble fraction ratio. These results demonstrated the primary role of the 70% ethyl alcohol-soluble fraction and HCl-soluble fraction, that is, the gliadin-rich fraction, in the expansion of yakifu.