GRANULE SIZE DISTRIBUTION AND CHEMICAL-COMPOSITION OF STARCHES FROM 12 SOFT WHEAT CULTIVARS

Granule size distribution of wheat starch is an important characterist ic that can influence its chemical composition, which in turn may affe ct its functionality. The granule size distribution and chemical compo sition of soft wheat starches were characterized and compared and rela tionships among those properties were identified. Thirty-four starch s amples from 12 soft wheat cultivars grown in the eastern half of the U nited States were examined. Granule size distribution was characterize d using a laser light-scattering technique. Amylose and phospholipid c ontents were determined using colorimetric procedures. A clear trimoda l distribution of granule sizes was shown by 26 out of 34 starch sampl es: small granules with diameters <2.8 mu m, midsize granules with dia meters of 2.8-9.9 mu m, and large granules with diameters >9.9 mu m. V olume% distribution of granules within the three size classes had rang es of 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 volum e% of granules within the ranges of 9.9-18.5 mu m and 18.5-42.8 mu m. Cultivar specific surface area means also differed. The environment af fected granule size distribution, with some cultivars exhibiting more variation than others. Pioneer 2555 was the least variable, whereas Pi oneer 2550 and Geneva were the most variable cultivars. Mean total amy lose (TAM), apparent amylose (AAM), and lysophospholipid (LPL) values varied significantly among cultivars. TAM was positively correlated wi th the volume% of granules of 9.9-18.5 mu m. LPL was negatively correl ated 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 differ ences exist in granule size distribution of softwheat starches and aff ect starch chemical composition. Data also suggest it is possible that lipid is preferentially associated with the biosynthesis of small sta rch granules.