Amylose and Amylopectin Interact in Retrogradation of Dispersed High‐Amylose Starches

Abstract

ABSTRACTRetrogradation of three high‐amylose starches (HAS: ae du, ae V, and ae VII) and common corn starch (CCS) was examined by dynamic oscillatory rheometry (7.5% [w/w] starch in 20% [v/v] dimethyl sulfoxide [DMSO]), differential scanning calorimetry (DSC; 30% [w/w] starch in water), and turbidity (0.5% [w/w] starch in 20% [v/v] DMSO). Nongranular lipid‐free starch and starch fractions (amylose [AM], amylopectin [AP], and intermediate material [IM]) were studied. Gels were prepared by dispersing starches or fractions in 90% DMSO and diluting with water, followed by storage for seven days at 4°C. For AM from each starch, the elastic modulus (G′) was similar when heated from 6 to 70°C. The G′ of HAS AP gels at 6°C was higher than for CCS AP gels. For nongranular CCS and ae du gels, G′ dropped dramatically (≈100×) when heated from 6 to 70°C, less (≈10×) for ae V gels, and least (≈5×) for ae VII gels. By DSC, each AM endotherm had a peak temperature of ≈140°C, whereas all AP endotherms were complete before 120°C. Endotherms >120°C were not observed for any nongranular starch despite the high AM content of some starches. After cooling starch suspensions from room temperature to 5°C and subsequent rewarming to room temperature, each AM and the ae VII nongranular starch remained highly turbid. Each AP and the remaining nongranular starches lost turbidity during rewarming. Our work suggests that branched molecules of CCS and HAS influence gel properties of nongranular starches by inhibiting or altering AM‐AM interactions.