WATER ADSORPTION ISOTHERMS AND ISOSTERIC HEAT OF SORPTION OF SPRAY DRIED AND FREEZE DRIED PASSION FRUIT PULP DEHYDRATED WITH CARRIERS AND SKIM MILK

Moisture equilibrium data of passion fruit pulp powders with maltodextrin and gum arabic obtained by two different drying methods (spray drying and freeze drying) were determined at 20, 30, 40 and 50 o C. Skim milk was used substituting part of these carriers in the samples. It were prepared one formulation using passion fruit pulp/maltodextrin/skim milk (PMS) and other using passion fruit pulp/gum arabic/skim milk (PGS). The behavior of curves was of type III, according to Brunauer’s classification and GAB model were fitted to experimental equilibrium data. The parameters obtained from GAB model was affected by the presence of carriers and showed distinct trends with variation temperatures. There are just little differences between two drying methods used in relation to equilibrium moisture content. The samples using maltodextrin or gum arabic had much little differences in equilibrium moisture content. Parameters values of the GAB equation also show the similarity between this study using skim milk and the other authors who used only the carriers commonly found in the literature (maltodextrin and gum arabic), showing that skim milk can be a good and cheaper substitute for these additives. It is observed a progressive increase in the heat of sorption in relation to decreasing moisture content and the values of different samples are all similar, comparing the relative equilibrium moisture content.