Changes in protein characteristics during the processing of wheat into flakes

Abstract

Wheat is subjected to various unit operations like soaking, steaming and tempering before flaking. During these processing operations, considerable changes in protein characteristics were observed as indicated by: (1) a lack of gluten formation in dough, and (2) a decrease in total protein extractability from 9.0 to 4.5% in SDS solution. However, the protein extractability of flakes was increased and their subunit pattern was found to be similar to that of whole wheat flour when the flake flour was treated with β-mercaptoethanol, indicating the formation of disulfide bonds on flaking. The SDS extracts on gel filtration chromatography showed a significant decrease in glutenin fraction and an increase in the 70 kDa molecular weight fraction and disappearance of the 45 kDa molecular weight fraction on flaking. In addition, an increase in the content of low molecular weight protein fractions (<25 kDa) was also observed. The SDS extract of flakes had more free sulfhydryl groups (18.5 µM) compared to that of wholewheat flour (6.2 µM). Variations in soaking, steaming and tempering periods produced only negligible changes in the protein extractability. However, increasing the soaking period from 6 to 18 h increased the sulfhydryl content from 13.3 to 18.5 µM, and increasing the steaming period from 10 to 20 min increased the yield of 15 kDa molecular weight protein fraction from 21 to 28%.