State diagram, sorption isotherm and color of blueberries as a function of water content

Abstract

A state diagram of blueberries was developed using freezing and glass transition curves, and maximal-freeze-concentration condition in order to predict the behavior and physical changes of fresh and lyophilized blueberries. Freezing points (Clausius–Clapeyron equation) and glass transition temperature (Gordon–Taylor equation) were measured by differential scanning calorimetry (DSC). Color samples were measured by computer vision system. Isotherms data was fitted using GAB, Peleg and Iglesias–Chirife equations.Glass transition decreased as decreasing solids content due to water plasticizing effect. Lyophilized and fresh samples varied their color; however thermal properties were similar, principally affected by their constituents although the blueberry's matrix state changed. Maximum-freeze-concentration conditions was found as X′s=0.69 kg solid (kg blueberry)−1, T′g=−54.86 °C and T′m=−45.45 °C. In conclusion, a state diagram was developed using lyophilized fruit but it can be extrapolated to whole blueberry fruit.