Thermodynamic sorption properties and glass transition temperature of tamarind seed mucilage (Tamarindus indica L.)

Adsorption isotherms for spray-dried tamarind seed mucilage were determined at 20, 30 and 40 °C and fitted to GAB and Caurie sorption models. The sorption properties were estimated using Kelvin and Helsey equations and the values found for the bound water were of 15.98, 11.33 and 9.87% and specific surface areas of 142.29, 133.97 and 133.14 m2/g at 20, 30 and 40 °C. The pore radius varied from 0.92 to 7.24 nm over the temperature range studied. The minimum integral entropy was observed at water activities of 0.11-0.21 and moisture contents between 2.17 and 2.29 kg H2O/100 kg d.s. Isokinetic theory suggested that the adsorption process was enthalpy driven. The glass transition temperature of the mucilage was found between 46.4 and 79.7 °C. SEM micrographs showed that the mucilage at water activities less than 0.75 was in a glassy state and able to retain its morphology. Therefore, it was suggested that by relating minimum integral entropy, moisture sorption and glass transition temperature in conjunction, it is feasible to extend the shelf-life of tamarind mucilage.