To dissect the most important determinant of wheat bread-making quality, gluten protein-types from 128 flours of organically grown German wheat varieties Bussard and Orestis were investigated by quantitative HPLC and SDS-PAGE procedures using protein standards. Both varieties exhibit great differences in gluten strength (> 34 %) at two locations and between two years determined by SDS-sedimentation volume (SDS-SV), a measure of bread-making quality. Unexpectedly, the results showed that neither concentrations of gliadin, gluten, HMW-glutenin or glutenin could explain the observed variation in SDS-SV even if protein concentrations were equal. In the case of glutenin this was found to be due to a low glutenin recovery resulting from a partial insolubility of glutenin in propanol (protein recoveries from 78 % to 95 %). Further investigations under the conditions of a complete glutenin extraction led to the identification and characterization of glutenin macropolymer (GMP) which affected the bread-making quality of wheat significantly. This effect was associated with higher molecular weights of GMP which may cause growing gluten networks compared to simple glutenin. Moreover, it was finally shown that quantitatively the concentrations of GMP (mg/100mg flour) were independent of protein concentrations. Our results demonstrate that, for the flour samples used, the flour GMP concentration is a key determinant, and together with the SDS-SV a reliable tool for bread-making quality prediction
