Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/22/1998
Publication Date: N/A
Interpretive Summary: Wheat starch exists as small granules composed of two main types of molecules. The size of the granules and the ratio of those two types of molecules affect their chemical composition and functionality. The granule size distribution, the type of molecule, and fat content of starches separated from soft wheats were studied. Significant differences were found in the granule size distribution and chemical composition of soft wheat starches. Wheat cultivar appears to be a determining factor of starch granule size distribution as well as the ratio of the two types of molecular components. However, variation within a cultivar indicates that environmental factors have significant effects on those properties. Some cultivars are more responsive to the environment than others and may require multiple environment testing to predict starch functionality. Correlations between granule size and the two types of molecular components show that very small granules are relatively rich in native fat and middle sized granules are rich in one of the two types of molecular components. Understanding the inherited variability in soft wheat starch physical properties will provide a means by which soft wheat breeders can produce wheat and desired starch properties. Correlations between starch physical properties and chemical composition provide a guideline for the genetic engineering of the mechanisms that could produce starches with tailored properties.
Technical Abstract: The granule size distribution and chemical composition of soft wheat starches from twelve soft wheat cultivars were characterized and compared. A clear trimodal distribution of granule sizes was shown by 26 out of 34 starch samples: small granules with diameters less than 2.8 #m, mid-size granules with diameters between 2.8 and 9.9 #m, and large granules with diameters greater than 9.9 #m. Volume% distribution of granules within the three size classes ranged between 9.7 - 15.2% (small), 13.4 - 27.9% (medium), and 57.9 - 76.9% (large). Highly significant differences were seen among the cultivars for volume% of granules within the regions of 9.9 - 18.5 #m and 18.5 - 42.8 #m. Cultivar specific surface area means also differed. The environment effected granule size distribution with some cultivars consistently varying more than others. Pioneer 2555 was the least variable, whereas Pioneer 2550 and Geneva were the most variable cultivars. Mean total amylose (TAM), apparent amylose, and lysophospholipid (LPL) values varied significantly among cultivars. TAM was positively correlated with the volume% of granules between 9.9 - 18.5 #m. LPL was negatively correlated with mean starch granule diameter and positively correlated with specific surface area of granules, indicating smaller granules tended to have higher lipid contents. Results suggest that significant differences exist in granule size distribution of soft wheat starches and affect starch chemical composition.