Dairy Chemistry- ICAR JRF/SRF 2024

• Effect of Strong Electrolytes on Aqueous Surface Tension:
• Gibbs Adsorption Isotherm:
• Strong inorganic salts ($\text{NaCl}, \text{KCl}$) are negatively adsorbed at the air-water interface because water dipole molecules strongly hydrate ions in the bulk phase.
• According to the Gibbs adsorption equation ($\Gamma \lt 0$), surface tension $\gamma$ increases slightly with electrolyte concentration.
• Conclusion: Increase (Option 1).

Correct option: (1) Increase

• Salting-Out of Casein with Sodium Chloride:
• Precipitation Behavior:
• Saturation of raw milk with sodium chloride ($\text{NaCl}$) at $37^\circ\text{C}$ quantitatively precipitates casein micelles by dehydrating hydrophobic patches and screening stabilizing surface charges, leaving whey proteins in the supernatant.
• Conclusion: Casein (Option 1).

Correct option: (1) Casein

• Number of Chiral Centers in Cholesterol:
• Stereochemistry of Cholesterol ($\text{C}_{27}\text{H}_{46}\text{O}$):
• Contains 8 asymmetric (chiral) carbon atoms:

• 3 (bearing the hydroxyl group)
• 8 (ring B/C junction)
• 9 (ring B/C junction)
• 10 (angular methyl group)
• 13 (angular methyl group)
  6. C-14 (ring C/D junction)
  7. C-17 (attached to side chain)
  8. C-20 (branched aliphatic tail)
  • Gives rise to $2^8 = 256$ theoretical stereoisomers.

• Conclusion: 8 (Option 3).