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Title: STRUCTURAL AND PHYSICOCHEMICAL CHARACTERISTICS OF WINTER SQUASH (CUCURBITA MAXIMA D.) FRUIT STARCHES AT HARVEST

Author
item Stevenson, David
item Yoo, Sang Ho
item HURST, PAUL - NEW ZEALAND INST
item JANE, JAY-LIN - IOWA STATE UNIVERSITY

Submitted to: Carbohydrate Polymers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2004
Publication Date: 1/10/2005
Citation: Stevenson, D.G., Yoo, S., Hurst, P.L., Jane, J. 2005. Structural and physicochemical characteristics of winter squash (cucurbita maxima d.) fruit starches at harvest. Carbohydrate Polymers. 59:153-163

Interpretive Summary: Starch characteristics from fruit of seven winter squash cultivars, grown in Iowa, were investigated. Squash starches had many distinctive features, including very uniform molecular size, narrow temperature range for melting of starch crystals, and high viscosity of starch pastes. The characterization of winter squash starches will enable future research to investigate the role of starch structure and functional properties in the texture of raw and cooked winter squash.

Technical Abstract: 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 micrometers, 6-8 micrometers, and 11-13 micrometers. Squash amylopectin had more long branch-chains (25.4-29.3% DP greater than or equal to 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 x 10^8 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 deg C to 63.5 deg C and enthalpy changes (delta-H) from 15.9 to 17.4 J/g. Retrogradation rate for squash starches ranged from 41% to 55% after 7 d at 4 deg C. Squash starch pastes, measured by using a Rapid Visco-Analyser, 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 deg C.