State diagram, water sorption isotherms and color stability of pumpkin (Cucurbita pepo L.)

Abstract

The state diagram and water sorption properties can be useful in assessing the stability of food products. In this study, we determined the initial freezing temperatures (Tf) and glass transition temperatures (Tg) of pumpkin using differential scanning calorimetry at various water contents. The vapor sorption analyzer was used to determine water sorption properties while the spectrophotometer used to measure color changes in pumpkin after 13 months of storage. We constructed a state diagram using Tf and Tg; and determined critical water activity from Tg, water content and water activity diagram. The Tf decreased from −1.3 to −21.0 °C as the solids content increased from 0.08 to 0.63 g solid/g pumpkin. The Tg decreased from 71.0 to −55.2 °C as the water content increased from 0.08 to 0.30 g.H2O/g pumpkin. The water sorption showed type III isotherm, while the monolayer ranged from 0.10 to 0.12 g.H2O/g dry-pumpkin. Pumpkin powder storage study indicated that color change increased with increasing water activity, while pumpkin color change was minimal in the glassy state. The state diagram and water sorption isotherm data may be utilized for the optimization of storage, processing, and packaging conditions of dehydrated or frozen pumpkin.