Studies on milling and baking quality and in-vitro protein digestibility of historical and modern wheats

There is considerable controversy among the public and the scientific community about whether modern wheats are harmful for human health and responsible for the increase of Celiac disease compared with historical varieties. Therefore, the milling and baking quality, protein digestibility, and protein composition of historical and modern wheats adapted to the Great Plains of the US were evaluated in this thesis. One objective of this thesis was to determine how end-use quality of wheat changed with wheat cultivar release year. Kernel physical characteristics, milling yield, whole-wheat flour quality, flour protein content, mixing quality and baking quality of 23 hard winter wheat cultivars released in the Great Plains region of the US between 1870 and 2013 were evaluated. Several quality characteristics improved across release year, which is evidence of the impact of plant breeding efforts over the years. Specifically, wheat kernels have become harder, moister, more uniform in hardness but more variable in shape over a century of breeding. Bran quality decreased, which may have implications for whole grain quality and milling productivity. The baking quality remained constant despite a strong decrease in protein concentration. Another objective was to determine the change in in vitro protein digestibility during breeding and its relationship with wheat end-use quality. Digestibility of bread increased with release year and was significantly positively correlated with kernel diameter standard deviation, milling yield, Mixograph mixing peak time, and loaf firmness while negatively correlated with white flour protein content, Mixograph mixing peak value, and loaf volume. Flour protein digestibility had no relationship with release year and no correlation with end-use quality characteristics. High molecular weight protein increased while low molecular weight protein decreased as a function of release year. Several gluten proteins were associated with high digestibility which may need further study. In conclusion, the end-use quality improved during breeding somehow and some of them have positive correlation with protein digestibility which can be used for future wheat breeding selection. Advisor: Devin J. Ros