Fluid Milk Processing & Preservation

Statement (I) is incorrect: Homogenization DECREASES the heat stability (coagulation time) of whole milk because newly created fat surface area adsorbs casein micelles, forming fat-protein complexes that are more susceptible to thermal bridging and heat coagulation. Statement (II) is correct: In skim milk (fat $\lt 0.1\%$), there are virtually no fat globule surfaces for micelle adsorption, so homogenization shear forces have negligible impact on its heat coagulation time.

Mechanisms and effects of milk homogenisation:

• Statement (I) is true because mechanical shearing, cavitation, and turbulence break down fat globules from $1\text{--}10\,\mu\text{m}$ to $\lt 2\,\mu\text{m}$.
• Statement (II) is false because homogenisation pressures ($10\text{--}25\text{ MPa}$) do not disintegrate intact casein micelles (which are tiny colloidal particles of $50\text{--}300\text{ nm}$); instead, casein micelles and subunits adsorb onto the expanded fat globule surface.
• Statement (III) is true because increased interfacial surface area and casein adsorption increase hydrodynamic volume and milk viscosity.
• Statement (IV) is true because thousands of tiny fat globules scatter light more effectively, giving homogenised milk a whiter, richer, and more opaque appearance.

Walker Formal method protein determination calculations:

• Volume of $0.1\text{ N NaOH}$ consumed in the second titration (formol titre, $V$):
  $$V = 3.4 - 2.5 = 0.9\text{ mL}$$
• Applying standard Walker empirical factors for $10\text{ mL}$ milk sample:
  $$\%\text{ Total Protein} = V \times 1.70 = 0.9 \times 1.70 = 1.53\%$$
  $$\%\text{ Casein} = V \times 1.34 = 0.9 \times 1.34 = 1.206\%$$
• Both values correspond exactly to % total protein: $1.53$ and % casein: $1.206$.
• Thus, option 1 is the mathematically correct choice.