Subtopic: Water activity, sorption and desorption isotherms
Question Statement:
Which of the following statements are TRUE regarding moisture sorption isotherms of agricultural and food products?
Options:
(A) At the same water activity ($a_w$), the equilibrium moisture content is higher along the desorption isotherm than the adsorption isotherm (hysteresis)
(B) Type II sigmoidal isotherms are characteristic of foods high in starch and protein
(C) At a given moisture content, water activity decreases with an increase in temperature
(D) The BET monolayer moisture content corresponds to the moisture level for optimal storage stability
Answer Key:
A, B, D
Step-by-Step Solution & Explanation
Sorption isotherm principles:
• Hysteresis loop: Desorption moisture > Adsorption moisture at identical $a_w$ due to ink-bottle capillaries and structural shrinkage (A is TRUE).
• Starchy/proteinaceous foods exhibit classical S-shaped Type II isotherms (B is TRUE).
• At a fixed moisture content, Clausius-Clapeyron equation dictates that water activity INCREASES with increasing temperature (C is FALSE).
• BET monolayer represents maximum coverage of polar sorption sites, below which lipid oxidation increases and above which browning/enzymatic rates accelerate (D is TRUE).