Subtopic: Glass transition temperature Tg and caking
Question Statement:
Spray-dried fruit juice powders cake and become sticky during ambient storage when:
Options:
(A) Storage temperature exceeds the glass transition temperature ($T > T_g$)
(B) Water activity is lower than 0.1
(C) Storage temperature is below $-40^\circ\text{C}$
(D) Relative humidity is 0%
Answer Key:
A
Step-by-Step Solution & Explanation
When temperature or moisture plasticization causes storage temperature to exceed the glass transition temperature ($T > T_g$), amorphous sugars transition from a glassy solid to a rubbery state, causing particle stickiness, caking, and collapse.