Question

Conversion of lactose glass to crystalline lactose causes defects in which type of milk product?

• A. Ice cream
• B. Sweetened condensed milk
• C. Milk powder
• D. Cheese

Hint:

Glass Transition in Dairy Powders: Amorphous Lactose Glass Crystallization $\rightarrow$ Causes CAKING AND LUMPING DEFECT in MILK POWDERS (due to moisture release and particle bridge fusion).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Amorphous glass state transitions in dairy powders: in spray-dried milk powder, lactose exists in a metastable amorphous glass state; exposure to moisture exceeding the glass transition temperature ($T_g$) induces spontaneous crystallization into $lpha$-lactose monohydrate, releasing free water that causes severe caking, lumping, and insoluble crusting.
Key Formula or Approach:
\[ \text{Spray-Dried Powder: Amorphous Lactose Glass} \xrightarrow{\text{Moisture Uptake / } T > T_g} \alpha\mathbf{\text{-Lactose Monohydrate Crystal}} \implies \mathbf{Caking, Lumping \& Loss of Solubility} \]

Step 2: Detailed Explanation:
In the physical chemistry and storage stability of dairy powders:
- In freshly spray-dried Milk Powder (Whole Milk Powder, Skim Milk Powder, Whey Powder):
- Ultra-rapid moisture evaporation in the spray dryer prevents lactose crystallization, locking lactose into a metastable, highly hygroscopic Amorphous Lactose Glass State.
- When milk powder is stored under unsealed or high-humidity conditions ($\text{RH} > 50\%$), moisture uptake depresses the glass transition temperature ($T_g$) below storage temperature.
- The amorphous lactose molecules mobilize and undergo spontaneous conversion from lactose glass to crystalline $\alpha$-lactose monohydrate.
- During crystallization, bound moisture is expelled to the surface, creating liquid bridges that bind adjacent powder particles into rock-hard aggregates, causing severe Caking, Lumping, Insoluble Crust Formation, and Loss of Dispersibility in Milk Powder (C).

Step 3: Final Answer:
Hence, conversion of lactose glass to crystalline lactose causes defects in Milk powder, matching option (C).