Technology of Milk & Milk Products

• Alkaline Phosphatase Reactivation in UHT Milk:
• Alkaline Phosphatase (ALP) is completely inactivated by standard pasteurization and UHT processing ($135-150^\circ\text{C}$ for a few seconds).
• However, upon storage at ambient temperature ($\gt 20^\circ\text{C}$), ALP can undergo reactivation (renaturation), yielding a false-positive phosphatase test.
• In direct UHT heating (steam injection or steam infusion followed by vacuum flash cooling), dissolved oxygen is thoroughly stripped from the milk.
• The lesser oxygen concentration (low dissolved $O_2$ / anaerobic reducing condition) preserves exposed free sulfhydryl ($-SH$) groups in the reduced state, preventing their irreversible oxidative loss and facilitating conformational refolding of the denatured ALP enzyme back to its catalytically active form.
• Correct Option: Option 1 (Presence of lesser oxygen concentration).

• Deteriorative Mechanisms in Skim Milk Powder (SMP):
• Maillard Browning Reaction:
• SMP contains approximately $50\%$ lactose (reducing carbohydrate) and $36\%$ protein (rich in free $\epsilon$-amino groups of lysine), with negligible fat ($\lt 1.5\%$).
• During storage—especially under elevated ambient temperature or moisture ($a_w \gt 0.2$)—non-enzymatic Maillard browning proceeds rapidly between reducing sugars and amino acid residues.
• Results in brown melanoidin pigments, stale/cereal off-flavors, insolubility, and loss of essential lysine bioavailability.
• Conclusion: Maillard browning (Option 4).

Correct option: (4) Maillard browning

• Thermodynamic Triple Point of Pure Water:
• Equilibrium State:
• The unique thermodynamic state where solid ice, liquid water, and water vapor coexist in simultaneous thermodynamic equilibrium.
• Exact Physical Constants:
• Temperature: $0.01^\circ\text{C}$ ($273.16\text{ K}$ or $32.018^\circ\text{F}$).
• Pressure: $611.657\text{ Pascals}$ ($6.11657\text{ mbar}$ or $4.587\text{ mmHg}$).
• Fundamental baseline reference for lyophilization (freeze drying) cycles in food engineering.
• Conclusion: Temperature: 0.01°C; Pressure: 611.657 pascals (Option 1).

Correct option: (1) Temperature: 0.01°C; Pressure: 611.657 pascals