Secagem de Uva Italia em leito fixo

AUTOR(ES)
DATA DE PUBLICAÇÃO

1998

RESUMO

The drying kinetics of the grape variety Italia was studied in this work, analysing the influence of air temperature and chemical pretreatments, using alkaline solution and ethyl oleate. The parameters not found in the literature for dryers project was obtained for grape, like bulk density as function of the moisture of product, volumetric shrinkage coefficient as function of the temperature and chemical pretreatments and equilibrium curves for skin and pulp of the grape separately. A study of grape skin permeability to water vapour was performed, considering the effects of the chemical pretreatments, glucose concentration, air temperature and skin thickness. A fixed bed dryer was used for the drying tests. In order to represent the drying kinetics curves, the Page s Equation was used and goód fits was obtained with determination coefficients near 1. Skin permeability to water vapour increased considerably with increasing concentration of pretreatment. The influence of glucose concentration became evident when a gradual increase of its levei caused a decrease in the skin permeability. Since minimum glucose concentration studied (10%) until the maximum (70%) the permeability decreased for less than half of it inicial value. The values of activation energy obtained for grapes with and without chemical pretreatment, were 6,94 KcallmolK and 7,46 KcallmolK respectively.Skin thickness showed a significant effect only in the absence of pretreatment, confirming the fact that the cuticular wax involving the fruits is an effective barrier to water vapour. Desorption isotherms were obtained at different temperatures (35, 40, 50, 60, 70 and 75°C), and both were well correlated with GuggenheimAnderson-de Soer Equation. The isosteric heat of sorption for skin and pulp of the grape was calculated using the equilibrium curves as a function of the humidity of the sample

ASSUNTO(S)

secagem permeabilidade uva

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