Bread Wheat Quality under Limiting Environmental Conditions: I-Molecular Properties of Storage Proteins and Starch Constituents in Mature Grains

Abstract

To support the introduction of local soft wheat varieties, the Lebanese state has implemented, during recent years, an improvement program to select plant material with good productivity in semi-arid conditions that can lead to national production that can, at the same time, meet quality needs expressed by Lebanese processors. In the present study, the main biochemical components of grains conventionally associated with bread-making properties (storage proteins, starch polysaccharides) were physiochemically characterized for a panel of local soft wheat varieties selected. During the two consecutive years of cultivation, the post-flowering thermal constraints significantly modified the kinetics of accumulation of the major constituents by mainly limiting the grain filling time. The level of polymerization/aggregation (i.e., gliadin/glutenin ratio, unextractable polymeric protein (UPP) amount, molecular weight average of glutenins) of prolamins was very high. The reduction in the amount of starch was accompanied by a significant change in the amylopectin/amylose ratio. Finally, the genotypes studied were characterized by significantly different distributions of starch granules; the percentage of the volume occupied by A-type and B-type starch granules varied between genotypes for the two cropping years. All these observations must be considered because of their determining role in the technological aptitude of the flours generated.