Adsorption and Desorption Kinetics of Deseeded Tamarind (Tamarindus indica L.) Fruit and Its Modeling Approach

Abstract

Adsorption and desorption characteristics of deseeded tamarind strip are very important to facilitate mechanization of deseeding and caking processes in the dry method of tamarind processing since the stickiness of tamarind is related to its hygroscopicity. Sorption studies of deseeded tamarind were conducted at 35°C and 40°C at the water activity range of 0.1–0.83 using the gravimetric method. The data were fitted with models viz., Henderson, Halsey, Iglesias and Chirife, Brunauer–Emmett–Teller (BET), and Guggenheim–Anderson–de Boer (GAB) models. The effective diffusivity coefficient was determined for desorption and adsorption kinetics of the isotherms using Fick's law, and the respective activation energy was also determined. The desorption and adsorption data fitted well with the GAB model followed by the Halsey model. It was observed that the adsorption and desorption monolayer moisture contents of deseeded tamarind fruits were found in the range from 12.58% to 19.38% on a dry basis according to the GAB model. The adsorption and desorption curve showed sigmoid and hysteresis behavior, which confirmed the presence of multilayer. The moisture diffusivity of tamarind ranged from 9.61 × 10⁻¹² to 3.10 × 10⁻¹¹ m²/s in adsorption and from 9.61 × 10⁻¹² to 1.25 × 10⁻¹¹ m²/s in desorption at 35°C. Similarly, the adsorption and desorption diffusivity ranged from 1.10 to 2.88 × 10⁻¹¹ m²/s and 8.13 × 10⁻¹² to 1.55 × 10⁻¹¹ m²/s, respectively, at 40°C. The study revealed that moisture diffusivity was higher during desorption compared to adsorption, and the activation energy needed for desorption was lower than that for adsorption.