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Size Distribution and Properties of Wheat Starch Granules in Relation to Crumb Grain Score of Pup-Loaf Bread¹

¹Cooperative investigations, U.S. Department of Agriculture, Agricultural Research Service, and the Department of Grain Science and Industry, Kansas State University. Contribution No. 04-007-J from the Kansas Agricultural Experiment Station, Manhattan, KS 66506. 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. ²Postdoctoral research associate and professors, respectively, Department of Grain Science and Industry, Kansas State University, Manhattan, KS 66506. ³Presently, research chemist, USDA-ARS Grain Marketing and Production Research Center, Manhattan, KS 66502. ⁴Research chemist and supervisory research chemist, respectively, USDA-ARS Grain Marketing and Production Research Center, Manhattan, KS 66502. ⁵Corresponding author. Phone: 785-776-2703; Fax: 785-776-2792; E-mail: okchung@gmprc.ksu.edu

Twelve hard winter wheat flours with protein contents of 11.8–13.6% (14% mb) were selected to investigate starch properties associated with the crumb grain score of experimentally baked pup-loaf bread. The 12 flours were classified in four groups depending on the crumb grain scores, which ranged from 1 (questionable-unsatisfactory) to 4 (satisfactory). Flours in groups 1, 2, 3, and 4 produced breads with pup-loaf volumes of 910–1,035, 1,000–1,005, 950–1,025, and 955–1,010 cm³, respectively. Starches were isolated by a dough handwashing method and purified by washing to give 75–79% combined yield (dry flour basis) of prime (62–71%) and tailing (7–16%) starches. The prime starch was fractionated further into large A-granules and small B-granules by repeated sedimentation in aqueous slurry. All starches were assayed for weight percentage of B-granules, swelling power (92.5°C), amylose content, and granular size distribution by quantitative digital image analysis. A positive linear correlation was found between the crumb grain scores and the A-granule sizes (r = 0.65, P < 0.05), and a polynomial relationship (R² = 0.45, P < 0.05) occurred between the score and the weight percentage of B-granule starch. The best crumb grain score was obtained when a flour had a weight percentage of B-granules of 19.8–22.5%, shown by varietal effects.