QUANTITATIVE-DETERMINATION OF GLIADIN SUBGROUPS FROM DIFFERENT WHEAT CULTIVARS

Sixteen wheat cultivars originating from different countries and genotypes and characterised by different technological properties were analysed for the amount and proportion of omega- and alpha-type and gamma-type gliadin subgroups. The optimal extraction of gliadin from flour was achieved with 60% (v/v) aqueous ethanol after pre-extraction with a salt solution. The separation and quantitative determination was performed by reversed-phase high-performance liquid chromatography on C-18 silica gel. The amount of both total gliadin and subgroups revealed distinct inter-cultivar differences. Within the subgroups, the alpha-type gliadins were generally present in greatest amount, followed by the gamma-type gliadins, whereas the omega-gliadins were present at lower levels. A strong statistical relationship was found between the protein content of the flours and the amounts of total gliadin, alpha-type and gamma-type gliadins. Other flour properties (baking volume, SDS-sedimentation volume, dough resistance and extensibility) were correlated only weakly with gliadin contents, with only omega 1,2-gliadins and gamma(A)- gliadins showing moderate negative and positive effects, respectively. The proportions of omega- and alpha-type and gamma-type gliadins found within the total gliadin fraction covered broad ranges (alpha: 43.9-59.9%, gamma: 30.5-45.6%, omega: 6.2-20.0%). The proportions of the gliadin subgroups were to some extent related to the genotype of the cultivar. Thus, high proportions of omega-gliadins (17-20%) were typical for wheat/rye hybrids. In view of the inter-cultivar variation observed, the value of immunochemical assays developed for the analysis of total gliadin in food is restricted if the reactivity of the antibodies used is not directed to all types of gliadin components but to the minor subgroups of omega-gliadins.