Abstract
The plant mangabeira (term referred for trees of mangaba fruit) is a tropical plant, native of Brazil, which has a great potential for economic exploration. In the state of Sergipe situated in the northeast region of Brazil, mangaba is one of the major fruit and very much sought in open markets, attaining even a price higher than that of grape and other noble fruits. The freezing, in general, offer several advantages over other methods of food preservation, among them, the maintenance of color, flavor and nutritional qualities, when the freezing is done properly and the process storage follows strict criterious to keep product quality. Generally, the experimental determination of thermal properties of foods is the major difficulty of the large dependence of these properties and their large deviations of low temperature characteristics of the freezing process. Due to various complications encountered in the experimental evaluation of thermal properties during freezing, efforts are concentrated on building mathematical models based on the thermodynamic properties of an ideal solution. The mathematical correlations of the thermal properties of food as a function of its basic chemical composition and water content have been an alternative to experimental procedures. Models for estimation of thermo physical properties for systems with and without phase changes are easily found in the literature. The values of specific heat, density and thermal conductivity were estimated using Choi and Okos model from the composition of mangaba experimentally determined. The lack of tabulated values of thermal properties of mangaba has restricted the use of equations in mathematical models for the calculation of thermal properties. The heat transfer at steady state is normally used as a hypothesis. In this work we used the hypothesis of heat transfer dynamics to estimate the coefficient of heat transfer using the Biot number relating to food thermal conductivity and the heat transfer coefficient. Afterwards, it was estimated the coefficient of heat transfer. This study aimed to evaluate the kinetics of freezing mangaba in half-ripe maturation stage. The diameters were 27.96 ± 0,7 mm for small ones and 52.63 ± .,36 mm for the big ones. The freezing time for small mangabas was 40 min while for the larger fruit was 69 min. The Plank model predicted freezing time of 39 min and 65 min respectively. The model proposed by Pham was not more suitable for the prediction of freezing time with average deviations between 14.5 % - 27.5 % compared to the experimental data.
