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

Abstract

Thermodynamic properties and glass transition temperature (Tg) 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 (qst) and differential entropy (Sd) were exponentially decreased with increasing moisture content (MC). Spreading pressure (φ) was increased with rising water activity (aw), but decreased with elevated temperature. Sodium alginate coating pretreatment decreased the qst, Sd 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 aw concept and glass transition theory, adsorption isotherm and Tg data were modeled and combined to establish state diagram. Compared with SA, the critical MC and aw 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.