Experimental data and predictive equation of the specific heat capacity of fruit juice model systems measured with differential scanning calorimetry

Abstract

Specific heat capacity ( $C_P$ ) is regarded as a fundamental parameter for the design, operation, and optimization of the heat transfer equipment widely used in the food industry. Using the calorimetric ASTM E1269-11 standard procedure, the $C_P$ -temperature ( $C_P\left(T\right)$ ) curves of fruit juice model systems prepared at different mass fractions of fructose/glucose/sucrose/citric acid/pectin and water were measured. Thus, experimental data of $C_P$ for solid samples in crystalline and amorphous states from -80 °C up to the melting temperature range and for aqueous samples from -80 to 110 °C were generated. In the tested temperature interval, the $C_P$ of crystalline, amorphous, and aqueous samples were found to be in the ranges of 0.037 ± 0.020 to 5.61 ± 0.04; 0.061 ± 0.004 to 3.12 ± 0.19, and 0.363 ± 0.05 to 3.24 ± 0.14 kJ/kg °C, respectively. Also, a generalized empirical equation based on the type and concentration of components was developed to predict the $C_P\left(T\right)$ curves of the studied samples. The proposed equation exhibited a low error sum of squares (SSE < 57.3) and a high coefficient of determination (R² > 0.927). An analysis of variance (ANOVA) was performed with a confidence level of 95% (p < 0.05). The $C_P\left(T\right)$ curves were influenced by temperature, thermal transitions, water, solid types, and compound interactions. Glucose was one of the solids that most significantly influenced the $C_P$ values of samples. PRACTICAL APPLICATION: The experimental specific heat capacity data and empirical equation proposed in this study are relevant to the design, evaluation, and optimization of heat transfer equipment involved in many foods and biochemical industrial processes such as cryopreservation, frozen storage, freezing, chilling, drying, and the cooking of hard candies.