Comparison of molecular structure and selected physicochemical properties of spelt wheat and common wheat starches

摘要

Molecular weight (M_w) and radii of gyration (R_g) of starch polysaccharide chains, distribution of amylopectin structural units, crystallinity, thermal properties, pasting viscosity profiles, susceptibility to α-amylolysis, swelling power and solubility of spelt and wheat starches isolated from commercially available spelt and wheat flours were studied. Average molecular weight M_w of polysaccharide chains eluted under the whole complex peak from high-performance size exclusion chromatography (HPSEC) column was found to be 0.829 × 10~7 g·mol~(-1) for spelt starch and 2.307 × 10~7 g·mol~(-1) for wheat starch. Significant differences in amylopectin chain length distribution between spelt and wheat starch were found. Shortest A type chains with M_w = 3.418 × 10~3 g·mol~(-1) and R_g = 65.4 nm constituted 88.2% of total mass of debranched spelt starch, whereas mass ratio of respective chains of wheat starch with M_w = 5.277 × 10~3 g·mol~(-1) and R_g = 88.2 nm was found to be 32.7%. Wheat starch was more susceptible to α-amylolysis than spelt starch. Enzymatic hydrolysis, rate constant for the first stage of hydrolysis (k_1 = 4.5 × 10~(-3) mg·ml~(-1)min~(-1)) and final hydrolysis extent (42.5%) for wheat starch were significantly higher than the respective values for spelt starch (k_1 = 2.3 × 10~(-3) mg·ml~(-1)min~(-1); 35%).