Propriedades termofísicas e secagem da polpa de noni e umbu.

Abstract

The knowledge of the thermophysical properties of agricultural products is of fundamental importance for engineering projects, since it provides information for the development and optimization of processes and equipment for their processing and storage. The aim of the present work was to determine the chemical, physicochemical and thermophysical characteristics (specific mass, specific heat, diffusivity and thermal conductivity) of the noni and umbu whole pulps and the combined pulps in different proportions, the drying kinetics of the mixed pulps at different temperatures (40, 50, 60 and 70 ºC) and the water adsorption isotherms of the powders of the combined noni pulp with umbu. The chemical and physico-chemical analyzes were determined according to the norms of the Adolfo Lutz Institute; the specific mass by the pycnometer method; the specific heat in the calorimeter of mixture; for the thermal diffusivity the Dickerson's cylinder was used and the thermal conductivity was indirectly determined with the results of specific mass, specific heat and thermal diffusivity. Drying was done in trays dryer, for the water adsorption isotherms the Aqualab was used and, from the isotherms, the isosteric sorption heat was calculated. The pulps of noni and integral umbu presented low lipid and protein content and predominance of yellow intensity; the whole noni pulp presented high ascorbic acid content. The specific masses of the whole umbu and noni pulps and the combined pulps showed reductions with increasing temperature. The specific heat showed a tendency of increase with temperature increase in all the whole and combined pulps. The umbu pulp showed higher thermal diffusivity than the noni pulp. The thermal conductivity of the pulps showed a tendency to increase with increasing temperature. The Page model was the best fit for experimental data on drying kinetics at temperatures of 40, 50, 60 and 70°C. The models adjusted to the water adsorption isotherms satisfactorily predicted the curves, with the GAB model, in general, obtaining the best adjustments and the isotherms were classified as Type II. There was a trend of reduction of the integral isosteric sorption heat with the increase of the equilibrium water content. The lower the equilibrium water content the greater the energy required to remove the water contained in the product.