Biochemical Basis of Flour Properties in Bread Wheats. I. Effects of Variation in the Quantity and Size Distribution of Polymeric Protein

Abstract

Abstract Relationships between the amount and size distribution of polymeric protein, as measured by size-exclusion HPLC (SE-HPLC), and flour properties were evaluated in four diverse sets of bread wheats representing recombinant inbred lines and cultivars. The recombinant inbred lines and a cultivar set were each grown at two different locations giving widely different flour proteins levels. The percentage of total polymeric protein (SE-HPLC peak 1) in protein or flour showed variable (insignificant to significant) relationships with flour properties, particularly dough strength as measured by the Brabender Extensograph (maximum resistance) and the National Mixograph (peak dough development time). On the other hand, the portion of the total polymeric protein unextractable in 0·5% SDS solution (i.e per cent unextractable polymeric protein in total polymeric protein) was very strongly positively correlated with dough strength properties in each of these sets, and accounted for the variation in these parameters to a much greater degree than did the per cent total polymeric protein in protein or in flour. SE-HPLC showed that the unextractable polymeric protein contained a significantly greater proportion of larger polymers (≥ 158k) than its extractable counterpart. Scanning of SDS-PAGE patterns of reduced-extractable and -unextractable polymeric protein fractions (peak 1 protein), indicated that the unextractable fraction had a significantly higher ratio of high Mr to low Mr glutenin subunits than the extractable fraction, suggesting that the molecular size distribution is shifted to higher molecular sizes as this ratio increases. Since the measurements of the relative size distributions of polymeric protein (per cent unextractable polymeric protein in total polymeric protein) or of total protein (relative amount of unextractable polymeric protein in total protein) also showed a wide genetic variance, and were independent of growth environment, they provide a reliable biochemical criterion for predicting dough strength of wheat on the basis of genetic differences in breeding programs. SE-HPLC provides a simple and an objective test for measuring the relative size distributions of the polymeric or total protein in wheat.