Date of Award
Doctor of Philosophy
Food Science and Human Nutrition
Starch structural and functional properties of 13 winter squash ( Cucurbita maxima D.) cultivars were investigated at harvest and after 5 or 10 weeks storage at 12°C. Texture profile analysis was carried out on winter squash fruit steamed at 6 different cooking times from 0 to 20 minutes, and for all three storage times. Buttercup squash cultivars had very high proportion of dry matter as starch (50--60%), whereas Halloween squash often accumulate no starch. Squash starches were B-type, with long amylopectin branch chain-lengths, low amylopectin polydispersity, gelatinization temperature of 60--65°C, and narrow range of gelatinization temperatures. Starch pastes had high peak and final viscosity, and high setback. Hardness of fruit was similar after 10 weeks storage, fracturability increased during storage and springiness of squash fruit decreased during storage. Correlations among squash starch structural and functional properties, and fruit textural attributes were observed. Starch content was positively correlated to fruit hardness and fracturability when raw and negatively correlated at long-duration cooking times. Springiness of raw and cooked fruit was negatively correlated to starch content. Apparent amylose content correlated negatively to hardness and fracturability of squash fruit, but absolute amylose content correlated positively to hardness and fracturability. Hardness and fracturability of squash fruit was consistently correlated to short (DP ≤ 12) and long (DP ≥ 37) amylopectin branch chain-lengths and negatively correlated to intermediate amylopectin branch chain-lengths (DP 13--36), regardless of storage time. Starch structural and functional properties, and textural attributes all varied among seasons. Ultrasound was transmitted through raw and cooked squash fruit as novel method of measuring texture. Ultrasonic velocity (UV) was slower than air for raw fruit, and despite softening during cooking, UV increased as squash were steamed. Light microscopy analysis showed fruit with fastest UV had cells engorged with gelatinized starch, whereas fruit with slower UV had no starch or other material in their cells. Zapallo fruit had dramatic variation in starch accumulation and could be used as model system for starch biosynthesis. Apple starches were also studied and were C-type with long amylopectin branch chains and low paste breakdown.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu
David Graham Stevenson
Stevenson, David Graham, "Role of starch structure in texture of winter squash (Cucurbita maxima D) fruit and starch functional properties " (2003). Retrospective Theses and Dissertations. 1465.