Abstract
Influences of protein content on the quantity and molecular size distribution of polymeric proteins were investigated by size-exclusion high-performance liquid chromatography using four wheat cultivars with different dough properties. As protein content increased, extractable monomeric proteins, consisting of mainly gliadins, increased most. With increasing protein content, extractable polymeric proteins that were small polymers increased more than unextractable polymeric proteins that were large glutenin polymers. Significant cultivar differences were found in the ratios of unextractable polymeric protein to total protein (UPP(%)) and to total polymeric protein (UPP/TPP (%)) which are the criteria of dough strength and in the regression slope of SDS-sedimentation volume against protein content. These results indicated that the degree of increase in dough strength with increasing protein content varied with the cultivars. These cultivar differences can be caused by the difference in the degree of increase in extractable or unextractable polymeric proteins due to the increase in protein content. The cultivars ‘Fukusayaka’ and ‘Nishinokaori’ had a significantly lower percentage of total polymeric protein in total protein, UPP (%) and UPP/TPP (%) and showed a larger increase in extractable polymeric protein and relatively smaller increase in unextractable polymeric protein with increasing protein content compared with the cultivars ‘Minaminokaori’ and ‘Norin 61’. Since these cultivars had null allele at the Glu-A1 locus, the difference in the molecular size distribution of polymeric proteins that contributed to the increase in protein might be explained by the presence or absence of glutenin subunits at the Glu-A1 locus.
