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Composition, Molecular Structure, Properties, and In Vitro Digestibility of Starches from Newly Released Canadian Pulse Cultivars

¹Guelph Food Research Centre, Agriculture and Agri-Food Canada, 93 Stone Road West, Guelph, ON, N1G 5C9, Canada. ²Corresponding author. Phone: 519-780-8030. Fax: 519-829-2600. E-mail address: liuq@agr.gc.ca ³Department of Biochemistry, Memorial University of Newfoundland, St. John's, NL, A1B 3X9, Canada. ⁴Crop Development Centre, University of Saskatchewan, Saskatoon, SK, S7N 5A8, Canada.

Pulse starches were isolated from different cultivars of pea, lentil, and chickpea grown in Canada under identical environmental conditions. The in vitro digestibility and physicochemical properties were investigated and the correlations between the physicochemical properties and starch digestibility were determined. Pulse starch granules were irregularly shaped, ranging from oval to round. The amylose content was 34.9–39.0%. The amount of short A chains (DP 6-12) of chickpea starch was much higher than the other pulse starches, but the proportions of B1 and B2 chains (DP 13-24 and DP 25-36, respectively) were lower. The X-ray pattern of all starches was of the C type. The relative crystallinity of lentil (26.2–28.3%) was higher than that of pea (24.4–25.5%) and chickpea starches (23.0–24.8%). The swelling factor (SF) in the temperature range 60–90°C followed the order of lentil ≈ chickpea > pea. The extent of amylose leaching (AML) at 60°C followed the order of pea ≈ chickpea > lentil. However, in the temperature range 70–90°C, AML followed the order of lentil > pea > chickpea. The gelatinization temperatures followed the order of lentil > pea > chickpea. The peak viscosity, setback, and final viscosity of pea starch were lower than those of the other starches. Lentil starch exhibited lower rapidly digestible starch (RDS) content, hydrolysis rate, and expected glycemic index (eGI). The resistant starch (RS) content of both lentil cultivars was nearly similar. However, pea and chickpea cultivars exhibited wide variations in their RS content. Digestibility of the pulse starches were significantly correlated (P < 0.05) with swelling factor (60°C), amylose leaching (60°C), gelatinization temperature, gelatinization enthalpy, relative crystallinity, and chain length distribution of amylopectin (A, B1, and B2 chains).