Enviromental influence on the expression of wheat protein fractions under South African drylands conditions

[摘要] English: Ten South African hard red wheat cultivars (BettaDN, Caledon, Elands, Gariep, Komati, Limpopo, Matlabas, PAN3118, PAN3349 and PAN3377) were planted at five localities over two seasons in the winter dryland wheat production area of South Africa. Localities were divided into North Western Free State (NW-FS) and Eastern Free State (E-FS). Size-exclusion high-performance liquid-chromatography was applied to determine the molecular weight distribution of SDS-extractable protein and SDS-unextractable protein fractions. Relative and absolute amounts were measured for glutenin, gliadin, albumin and globulin.Protein fractions did not increase parallel to increased flour protein content. The gliadin fraction showed the highest correlation in NW-FS, while polymeric proteins showed the highest correlation in E-FS with flour protein content. Albumin and globulin showed the lowest correlation with flour protein content in both regions. Environment made the largest contribution to variation in flour protein content in both regions.Bread making properties were correlated with flour protein content and protein fractions. Significant positive correlations were observed between flour protein content and wet gluten content, farinograph water absorption, alveograph extensibility, alveograph strength and loaf volume. Significant negative correlations occurred between flour protein content and SDS-sedimentation and alveograph tenacity. Mixograph peak time was mainly influenced by genotype and did not correlate significantly with flour protein content, while unextractable polymeric proteins showed a significant positive correlation with mixograph peak time. Partial correlations were conducted to remove the quantitative effect of flour protein content. Polymeric and monomeric protein fractions affected bread making quality differently in NW-FS than E-FS, indicating the effect of environment on protein composition.Pearson's correlation showed that flour protein content correlated between significantly and not significantly with alveograph tenacity, alveograph extensibility and mixogrpah peak time MPT for individual cultivars. The stepwise multiple linear regression indicated that flour protein content could only explain variation in alveograph extensibility and loaf volume for two cultivars in E-FS. Protein fractions contributed in different degrees to variation for alveograph tenacity, alveograph extensibility, mixograph peak time and loaf volume for individual cultivars and between the two regions. The model explained a larger percentage of variation in alveograph extensibility for BettaDN, Caledon, Elands, Gariep, Komati and Limpopo in E-FS than in NW-FS, while the model explained a larger proportion of variation in mixograph peak time for Matlabas and the Pannar cultivars in NW-FS than in E-FS. Albumin and globulin fractions contributed more to variation for alveograph tenacity, alveograph extensibility and mixograph peak time in NW-FS than in E-FS. The effect of albumin and globulin on baking quality justifies further research.Environment had a large influence on flour protein content and percentages of protein fractions. Protein fractions affected baking quality differently between environments and genotypes.

[发布机构] University of the Free State