Influence of the microstructure and composition on the thermal–physical properties of hard candy and cooling process

Abstract

In this paper, glass transition temperature (Tg) and microstructure of hard candy honey flavored have been investigated using differential scanning calorimetry (DSC) data and scanning electron microscopy images (SEM) respectively. Precisely, the glass transition temperature can be used as reference temperature to determine the operating mode of processing stages. In fact, the temperature at which hard candies may leave the cooling stage has to be equal or lower than 34°C in order to ensure the glassy state and therefore improve product shelf life; due to the fact that the experimental results indicated a temperature range of glass transition of 35.36 ± 1.48 - 36.37 ± 1.63 °C. As regards to the microstructure, SEM images reveal overlapping of layers at samples edges which could be attributed to the water absorption from the environment leading to storage problems, like crystallization. In addition, micrographics also reveal the presence of air bubbles which may negatively affect the temperature profile inside the candy and consequently may change the operating mode of the cooling equipment. The influence of the air bubbles on the thermal conductivity of the candy is also investigated.