Sodium alginate coating pretreatment improved storage stability of heat pump dried scallop adductors: from thermal and thermodynamic points of view

Thermodynamic properties and glass transition temperature ( T g ) of heat pump dried scallop adductors with (SA-C) and without (SA) sodium alginate coating pretreatment were investigated. Single sodium alginate film (SF) was also performed for comparison. The isotherms for SA, SA-C and SF followed type II characteristics. Water adsorption capacity of SA was decreased with coating pretreatment. The net isosteric heat of adsorption ( q st ) and differential entropy ( S d ) were exponentially decreased with increasing moisture content (MC). Spreading pressure ( φ ) was increased with rising water activity ( a w ), but decreased with elevated temperature. Sodium alginate coating pretreatment decreased the q st , S d and φ of SA. The enthalpy–entropy compensation theory can be employed for the adsorption behaviors of 3 samples. It was enthalpy-driven non-spontaneous for SA, and enthalpy-driven spontaneous for SA-C and SF, respectively. Based on the a w concept and glass transition theory, adsorption isotherm and T g data were modeled and combined to establish state diagram. Compared with SA, the critical MC and a w were, respectively, increased 7.14% and 187.5% with coating pretreatment. Hydrocolloids coating is an innovative pretreatment in enhancing the storage stability of dried foods.