|Tilley, Michael - Mike|
Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/1999
Publication Date: N/A
Citation: N/A Interpretive Summary: Soft wheats grown in the eastern U.S. differ in the average size of their starch granules and in the chemical composition of the granule itself. However, those differences have not been studied to determine how they may affect important milling and baking qualities expected among quality soft wheats. We studied those differences in twelve classically popular soft wheats from which starch was isolated from the kernels. Starch slurries were heated and cooled while their viscosity was measured. After cooling the starches formed a thickened gel that was evaluated for firmness. Even though the particle size of softer wheats tends to be smaller than harder wheats, the particle size of the starch granules of softer wheats tends to be larger than those from harder wheats. In part, this may explain why wheats vary in texture. The viscosity of heated starch slurries was affected by the carbohydrate composition of the molecules. Thinner viscosities and stronger gels were produced by wheats that had more amylose and less amylopectin. The milling softness of the wheats and the amount of flour produced from them were also associated with granule composition. These findings demonstrate that the soft wheat breeder, miller and baker could exploit to their benefit natural differences in starch qualities found among soft wheat cultivars. The whole wheat industry will benefit by knowing why some wheats are softer that others.
Technical Abstract: Starches were isolated from twelve soft wheat cultivars and characterized for waxy (Wx) allelic expression and thermal pasting characteristics. Gels were produced and evaluated using deformation rheological measurements. Those data were compared to cultivar kernel texture, milling characteristics, starch chemical analyses and flour pasting characteristics. Flour yield was found to be negatively associated with amylose content and smaller granule size. Higher starch pasting viscosities associated with lower amylose content. Lower starch pasting times and temperatures associated with lower levels of lipid- omplexed amylose, lower phospholipid content, lower flour protein content, smaller starch granule surface area, softer kernel texture and higher levels of total starch. Increased gel hardness positively correlated with amylose content and negatively correlated with kernel texture. The cultivar Fillmore, which had partial waxy mutation at the B allele, produced the highest peak pasting viscosity and the weakest gel strength. Flour pasting breakdown was correlated with higher starch amylose content. Flour pasting values were better correlated than starch pasting values with amylose and lipid contents and with starch gel hardness. Softer kernels negatively correlated with lipid-complexed amylose content and phospholipid content and positively correlated with total starch. Milling of softer textured wheats produced smaller flour particle size but larger starch granules. In part, this may explain why soft wheats vary in texture.