Effect of maltodextrins on water adsorption and glass transition of spray dried soy sauce powders

Soy sauce powders were made by spray drying liquid soy sauce using maltodextrin as the drying aid. Maltodextrins of DE 5, DE 10 and DE 15 with concentrations of 20% and 40% (w/v) were incorporated into the soy sauce, respectively, as a carrier. The moisture adsorption isotherms of the powders with and without maltodextrins were studied. Tg of the powders were determined using a differential scanning calorimeter (DSC) after being equilibrated under various water activities. Brunauer-Emmett-Teller (BET) equation and Gordon-Taylor equation were used to model the experimental data of moisture adsorption and Tg, respectively. It was found that the spray dried soy sauce powder was very hygroscopic in nature. Incorporating maltodextrins could significantly reduce the hygroscopicity of the soy sauce powders, with higher maltodextrin concentration resulting in lower equilibrium moisture content. The BET equation was found to be able to model the moisture adsorption results of all soy sauce powders up to aw of 0.84. The plasticizing effect of water on the glass transition temperature of soy sauce powders was observed. Increasing equilibrium moisture content could significantly reduce the value of Tg. The experimental data of Tg fitted the Gordon-Taylor model well. The predicted Tg value of soy sauce dry matter was at 45.4C which was much lower than that of the soy sauce powders added with 40% maltodextrins.