Subtopic: Water activity, sorption and desorption isotherms
Question Statement:
The net isosteric heat of sorption ($q_{st} = Q_{st} - \lambda$, where $\lambda$ is the latent heat of vaporization of pure water) calculated from the Clausius-Clapeyron equation $\left[ \frac{d(\ln a_w)}{d(1/T)} = -\frac{q_{st}}{R} \right]$ physically signifies:
Options:
(A) The extra binding energy with which water molecules are bound to sorption sites in the food matrix compared to bulk liquid water
(B) The sensible heat required to melt food fat globules
(C) The heat of combustion of food protein
(D) The kinetic energy dissipated during mechanical spray drying
Answer Key:
A
Step-by-Step Solution & Explanation
The net isosteric heat of sorption ($q_{st}$) represents the excess enthalpy of binding between water and the solid food matrix over that between water molecules in pure liquid state; it increases sharply as moisture content drops toward monolayer coverage.