Subtopic: Glass transition temperature Tg and caking
Question Statement:
In dehydrated powdered food products (such as spray-dried milk powder and fruit juices), stickiness, caking, and collapse occur when storage temperature rises above:
Options:
(A) Glass transition temperature ($T_g$)
(B) Boiling point of water
(C) Sublimation point of dry ice
(D) Critical point of carbon dioxide
Answer Key:
A
Step-by-Step Solution & Explanation
Amorphous food powders exist in a rigid, stable 'glassy' state below their glass transition temperature ($T_g$). When ambient temperature rises above $T_g$ (or when moisture absorption plasticizes and lowers $T_g$ below room temperature), the powder transforms into a mobile 'rubbery' state, leading to stickiness, inter-particle bridging, and caking.