Desenvolvimento e validação de metodologia para determinação de propriedades termofísicas em alimentos

Abstract

Thermal processes are among the most important techniques of food preservation. In the processing, properties such as density, thermal conductivity, specific heat and thermal diffusivity present substantial changes depending on the composition, temperature and physical structure of the food. Due to the scarcity of these data or differences between methods of determination, it is necessary to evaluate the efficiency of the procedures in the laboratory routine. Such evaluation involves a process known as validation, which considers the relationship between experimental results and the questions that the method must answer. Validation is used for the development of an analytical method, adaptation or implementation of a known method. The method is considered validated only if its characteristics agree with the established prerequisites, thus there is a difference between the execution of experiments and the validation. The present work had the objective of developing and validating a methodology for the determination of specific heat and thermal diffusivity in foods through the parameters linearity, precision and accuracy and to use the experimental data of density, specific heat and thermal diffusivity for determination of thermal conductivity in food. The samples used were commercial pulp of mandarin in different contents of total soluble solids. The actual density was obtained using pycnometer and analytical balance. Specific heat was obtained by the blends method. The thermal diffusivity was obtained using an aluminum tube, sensors and thermostatic bath. The thermal conductivity was also obtained indirectly through the combination of experimentally determined parameters. The average specific heat value found for the mandarin pulp containing seven different dilutions was 2,276 ± 0,209 J / kg ºC, the average value of the thermal diffusivity was 1.75x10- 7 ± 8.975x10-9 m² /s and value obtained for the thermal conductivity was 0.415 ± 0.0305 W / m. Regarding the validation parameters of the specific heat experiment, although some presented acceptable values, when compared with the literature, the validation of this method was not considered, since most of the values of precision were above the recommended and high values of experimental error. For the determination of the thermal diffusivity, the calculated validation parameters presented coherent answers with the literature, so it may be possible to consider the validation of the experiment.