Analysis of the effect of sugars and organic acids on the ice melting behavior of pitanga and araza pulp by differential scanning calorimetry (DSC)

Most Brazilian fruits are highly perishable but in frozen state would have the potential to be developed into a variety of commercially viable products. Pitanga and araza were investigated to determine the effect of composition on the freezing behavior using differential scanning calorimetry (DSC). The effect of low molecular weight compounds on the ice melting temperature T_m was investigated for: 1. Whole fruit pulp (WP); 2. Soluble fractions (SF) isolated by centrifugation from WP; and 3. Simulated systems (SS) prepared only with sugars (glucose, fructose and sucrose) and organic acids (citric, malic, and tartaric acids) as they occur in WP. Ice melting temperatures (T_m) were determined for WP, SF and SS over the range of concentrations between 10 wt. % (T_m = -0.19 °C for both for araza and pitanga) and 40 wt. % T_m = -5.0 °C and -7.05 °C for araza and pitanga, respectively). The T_m data could be fitted using the Chen equation, (C.S. Chen, J. Food Sci. 50 (1985) 1158–1162) for both fruits for WP, SF and SS. Deviations between the predictions of the Chen equation and T_m data are observed for the highest concentration studied (40 wt. %); these deviations can be minimized by fitting the parameters of the Chen equation to the experimental data rather than calculating them based on the molecular properties and composition of the system. We observe that the sugars have the highest impact on the melting behavior, with, in the concentration ranges investigated, a limited effect of organic acids. Using the lever rule, the weight fraction of ice is calculated from ice melting curves as a function of concentration and temperature. Both then ice melting line and the ice fractions are important in developing formulations have the desired freezing behavior as well as determining the processing and storage conditions in the frozen state.