Milk Powder Chemistry: Glass Transition, Lactose Crystallization, Free Fat & Caking

• Mass Transport through Food Packaging Polymers:
• Pressure dependence: Gas permeability ($P = D \times S$) through polymeric barriers increases as pressure differential increases due to higher gas solubility and matrix plasticization.
• Temperature dependence: Gas diffusion coefficient increases exponentially with temperature according to Arrhenius kinetics ($D = D_0 e^{-E_d/RT}$).
• Polymer polarity: Non-polar hydrocarbon polymers (Polyethylene - LDPE/HDPE, Polypropylene) lack hydrophilic groups, exhibiting excellent water vapor barrier properties (low WVTR).
• Statement C is false: Polar polymers (EVOH, cellophane, polyamide) absorb moisture and possess poor water barrier properties.
• Conclusion: A, B, D only (Option 2).

Correct option: (2) A.B,D only

• Physical State of Lactose in Spray-Dried Milk Powder:
• Amorphous Glass State:
• In spray drying, moisture evaporates within seconds, causing rapid viscosity rise that freezes lactose molecules into an amorphous, non-crystalline glass state.
• Amorphous lactose glass is thermodynamically metastable and hygroscopic; moisture absorption above critical water activity ($a_w \gt 0.43$) triggers crystallization into $\alpha$-lactose monohydrate, causing powder caking.
• Conclusion: Glass (Option 3).

Correct option: (3) Glass

• Whey Protein Nitrogen Index (WPNI) Classification:
• ADPI Standards for Nonfat Dry Milk:
• Measures undenatured whey protein nitrogen per gram of powder ($\text{mg WPN/g}$):
• Low-Heat Milk Powder: $\ge 6.0\text{ mg WPN/g}$ (very low level of protein denaturation).
• Medium-Heat Milk Powder: $1.5 - 5.9\text{ mg WPN/g}$.
• High-Heat Milk Powder: $\le 1.5\text{ mg WPN/g}$ (severe denaturation).
• Conclusion: ≥ 6.0 (Option 2).

Correct option: (2) 26.0