Water Desorption Isotherms of Raw and Osmotically Dehydrated Garlic

Abstract

Water desorption isotherms of raw and osmotically dehydrated (at 25ºC, for 2 hours, with 10 and 26% NaCl solutions) garlic slices at different temperatures (25, 40, 55, and 70ºC) were experimentally determined over a range of water activity of 0.05–0.90 using a static gravimetric method. Desorption isotherms can be classified as Type III. The water desorption isotherms of raw garlic clearly showed the influence of temperature i.e. increasing water activity at a fixed moisture content with increasing temperature; whereas for the osmotically dehydrated garlic the effect of the temperature was less important. The increase of NaCl content in osmotically dehydrated garlic led to a decrease in water activity at the same moisture content, and this effect was more accentuated at high temperatures. Equilibrium moisture content data at each temperature were satisfactorily fitted with Henderson model and a six-parameters equation based on Henderson model was obtained in order to correlate simultaneously moisture content with water activity, temperature, and osmotic solution concentration. A prediction model based on concentration and physical state of garlic compounds was successfully used to reproduce the experimental data. Keywords: Drying, Equilibrium moisture content, Modelling, Water activity