Subtopic: Water activity, sorption and desorption isotherms
Question Statement:
Which of the following factors increase the rate of non-enzymatic browning (Maillard reaction) in concentrated dairy products like sweetened condensed milk and khoa during thermal storage?
Options:
(A) Water activity maintained in the intermediate moisture range ($0.65 < a_w < 0.80$)
(B) Presence of reactive reducing sugars (lactose) and free amino groups (lysine residues of casein)
(C) Alkaline or higher pH levels ($pH > 7.0$)
(D) Storage at sub-zero temperatures ($-25^\circ\text{C}$) under complete darkness
Answer Key:
A, B, C
Step-by-Step Solution & Explanation
Maillard reaction rates peak at intermediate $a_w$ ($0.65-0.80$, A), require reducing sugars and amino groups (B), and accelerate under unprotonated alkaline amino states (C). Frozen storage at $-25^\circ\text{C}$ (D) completely arrests the reaction.