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Measurement of Wheat Starch Granule Size Distribution Using Image Analysis and Laser Diffraction Technology

¹USDA-ARS, Grain Marketing and Production Research Center, Manhattan, KS 66502. Names are necessary to report factually on available data however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable. ²Corresponding author. Phone: 785-776-2763. Fax: 785-537-5534. E-mail: jeff.wilson@gmprc.ksu.edu ³Kansas State University, Department of Plant Pathology, Manhattan, KS 66506. ⁴Kansas State University, Department of Grain Science, Manhattan, KS 66506.

Starch was isolated from flour of four wheats representing hard red winter (Karl), hard red spring (Gunner), durum (Belfield 3), and spelt (WK 86035-8) wheat classes. Digital image analysis (IA) coupled with light microscopy was used to determine starch size distributions where the volume of granules was calculated as spherical particles or oblate spheroids. Starch granules were classified into three size ranges: A-type granules (> 15 μm), B-type granules (5–15 μm), and C-type granules (<5 μm). An error was noted in using digital image analysis because the perimeter of some granules touch the edge (PTE) of the field being analyzed. To correct for this error, the PTE granules were manually replaced into the field by measuring their diameters and entering them into the database. The results showed differences in the starch size distributions between the classes of wheat evaluated, as well as the method of analysis. Four laser diffraction sizing (LDS) instruments were used to measure granule distributions of the four classes of wheat. LDS compared with IA resulted in a ≈40% underestimation of the A-type granule diameter and a ≈50% underestimation of the B-type granule diameter. A correction factor (adjustment) was developed from IA data to correct LDS analysis. LDS data correlations before adjustments to IA data were R² = 0.02^ns to 0.55***. After adjustment, these correlations improved to R² = 0.81*** to 0.93*** depending on the class of wheat starch evaluated.