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Differences in Starch Granule Composition and Structure Influence In Vitro Enzymatic Hydrolysis of Grain Meal and Extracted Starch in Two Classes of Canadian Wheat (Triticum aestivum L.)

¹Department of Plant Sciences, College of Agriculture and Bioresources, 51 Campus Drive, University of Saskatchewan, Saskatoon, SK, S7N 5A8, Canada. ²Crop Development Centre, College of Agriculture and Bioresources, 51 Campus Drive, University of Saskatchewan, Saskatoon, SK, S7N 5A8, Canada. ³Corresponding author. Phone: (306) 966-4969. Fax: (306) 966-5015. E-mail: ravi.chibbar@usask.ca

Starch granule composition and amylopectin structure affect starch digestibility, an important factor influencing wheat grain utilization for human food consumption. Six bread wheat cultivars with four belonging to the Canada Western Red Spring (CWRS) and two Canada Prairie Spring Red (CPSR) market classes were analyzed for the relationship between their grain constituents and in vitro enzymatic hydrolysis of starch. CPSR cultivars had higher starch and amylose concentrations compared with CWRS cultivars, which had a higher protein concentration. Starch granule size distribution did not differ among the genotypes, except AC Foremost, which had significantly (P < 0.05) higher volume percent of B-type starch granules (≈15%) and lower volume percent of A-type starch granules (≈9%) compared with other cultivars. Fluorophore-assisted capillary electrophoresis revealed a lower content of R-IV (DP 15–18, ≈6%) and a higher content of R-VII (DP 37–45, ≈7%) chains in the CPSR cultivars compared with the CWRS cultivars. Starch in vitro enzymatic hydrolysis showed that compared with CWRS cultivars, the two CPSR cultivars had reduced amounts of readily digestible starch and higher amounts of slowly digestible starch and resistant starch. Consequently, the two CPSR cultivars also showed lower hydrolysis indexes in grain meal as well as extracted starch. CPSR cultivars, with higher starch and amylose concentrations, as well as a higher content of long chains of amylopectin, showed a reduced starch in vitro enzymatic hydrolysis rate.