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Granule Size Distribution and Chemical Composition of Starches from 12 Soft Wheat Cultivars

¹U.S. Department of Agriculture, Agricultural Research Service, Soft Wheat Quality Laboratory, 1680 Madison Ave., Wooster, OH 44691. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of a product by the U.S. Department of Agriculture, and does not imply its approval to the exclusion of other products that also can be suitable. ²Corresponding author. E-mail: gaines.31@osu.edu

Granule size distribution of wheat starch is an important characteristic that can influence its chemical composition, which in turn may affect its functionality. The granule size distribution and chemical composition of soft wheat starches were characterized and compared and relationships among those properties were identified. Thirty-four starch samples from 12 soft wheat cultivars grown in the eastern half of the United States were examined. Granule size distribution was characterized using a laser light-scattering technique. Amylose and phospholipid contents were determined using colorimetric procedures. A clear trimodal distribution of granule sizes was shown by 26 out of 34 starch samples: small granules with diameters <2.8 μm, midsize granules with diameters of 2.8–9.9 μm, and large granules with diameters >9.9 μm. Volume% distribution of granules within the three size classes had ranges 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 volume% of granules within the ranges of 9.9–18.5 μm and 18.5–42.8 μm. Cultivar specific surface area means also differed. The environment affected granule size distribution, with some cultivars exhibiting more variation than others. Pioneer 2555 was the least variable, whereas Pioneer 2550 and Geneva were the most variable cultivars. Mean total amylose (TAM), apparent amylose (AAM), and lysophospholipid (LPL) values varied significantly among cultivars. TAM was positively correlated with the volume% of granules of 9.9–18.5 μm. 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. Data also suggest it is possible that lipid is preferentially associated with the biosynthesis of small starch granules.