Structural and physicochemical characteristics of winter squash (Cucurbita maxima D.) fruit starches at harvest

Structures and physicochemical properties of starch isolated from fruit (pepo) of seven winter squash cultivars (Cucurbita maxima D.) were studied. Squash starches exhibited the B-type X-ray diffraction pattern and had most granules with diameters of 1.5-2.5, 6-8, and 11-13 μm. Squash amylopectin had more long branch chains (25.4-29.3% DP≥37), and squash starch had relatively small absolute amylose contents (12.9-18.2%). Squash starch amylopectins had weight-average molecular weights ranging from 2.03 to 3.22×108 g/mol, gyration radii of 294-337 nm, and unusually low polydispersity (1.21-1.81). Isoamylase-debranched amylopectins showed average chain-length varied from DP 26.5 to 28.1. Squash starches had onset gelatinization temperature ranging from 60.6 to 63.5 °C and enthalpy changes (ΔH) from 15.9 to 17.4 J/g. Retrogradation rate for squash starches ranged from 41 to 55% after 7 days at 4 °C. Squash starch pastes, measured by using a Rapid Visco-Analyzer, had peak viscosity of 174-233 RVU, final viscosity of 193-244 RVU, and setback of 79-100 RVU, with pasting temperature of 65.6-68.8 °C.