Modeling the Effect of Glucose Syrup on the Moisture Sorption Isotherm of Figs

Moisture sorption isotherms of figs with and without glucose syrup (at 20% and 40%, w/w) were determined at 5 °C, 25 °C, and 40 °C. A static gravimetric method was used under 0.11-0.84 water activity ranges for the determination of sorption isotherms that were found to be typical type III for control sample. The inclusion of glucose syrup had significant effects on the sorption isotherms, and the moisture content of samples at each awdecreased with increasing temperature. The experimental data were fitted well with two-parameter Brunauer-Emmet-Teller, three-parameter Guggenheim-Anderson-de Boer, and four-parameter Peleg models that all had R2of greater than 0.99. The net isosteric heats of sorption were estimated using the Clausius-Clapeyron equation from the equilibrium data at different temperatures. It was found that the addition of glucose syrup significantly increased the amount of monolayer water and the isosteric heat of sorption. Both water activity and isosteric heat of sorption increased with glucose syrup level and the shape and status of sorption isotherms tend to change toward the typical sigmoid shape of most food systems.