Which of the following property is not desirable in Infant milk... | Agrigyan

Flavor chemistry of lipid peroxidation in milk fat:

• Lipid autoxidation initiates with free radicals generating primary hydroperoxides (ROOH). However, hydroperoxides themselves are completely odorless and tasteless.
• Hydroperoxides are chemically unstable and undergo homolytic $\beta$-scission cleavage to produce short- and medium-chain volatile secondary carbonyl compounds, primarily Aldehydes (hexanal, nonanal, 2-nonenal) and Ketones (methyl ketones, vinyl ketones). These volatile carbonyls have extraordinarily low odor thresholds (parts per billion) and are directly responsible for the repulsive, metallic, cardboard, and paint-like oxidized off-flavors in ghee.

Thermal severity hierarchy in dairy product manufacturing:

• Khoa (B): Subjected to extensive open-pan boiling, continuous evaporation, and high heat desiccation ($\gt 100^\circ\text{C}$ for extended periods), producing severe Maillard browning, massive whey protein denaturation, and lactosylation (highest heat changes).
• Paneer (A): Milk is heated to $85\text{--}90^\circ\text{C}$ for 5 minutes prior to acid coagulation at $70^\circ\text{C}$, inducing significant whey protein denaturation ($\gt 75\%$) and coprecipitation with casein.
• Chakka (C): Prepared by fermenting pasteurized milk ($72^\circ\text{C}$ for 15 s) into dahi at mesophilic temperatures ($22\text{--}30^\circ\text{C}$) followed by whey drainage.
• Acid casein (D): Coagulated at mild isoelectric precipitation temperatures ($43\text{--}45^\circ\text{C}$) using dilute mineral acid from skim milk with minimal thermal exposure.

Enzymatic and non-enzymatic phases of milk renneting:

• Statement (I) is correct: The primary (enzymatic) phase of rennet coagulation involves the specific cleavage of the Phe105-Met106 peptide bond in micellar surface $\kappa$-casein by chymosin. This releases the hydrophilic caseinomacropeptide (CMP) into whey, leaving hydrophobic para-$\kappa$-casein on the micelle core.
• Statement (II) is correct: The secondary (non-enzymatic) phase is the calcium-dependent aggregation phase. Once $\gt 85\%$ of $\kappa$-casein is cleaved, colloidal steric stability is lost. Divalent calcium ions ($Ca^{2+}$) neutralize negative charges and form salt bridges between adjacent para-casein micelles, cross-linking them into a three-dimensional gel network (clot). Without sufficient free $Ca^{2+}$, coagulation does not occur even if the primary phase is complete.

Thermodynamic heat stability and denaturation kinetics of whey proteins:
When measured by irreversible loss of solubility upon heat treatment:

• Immunoglobulins (B): Most heat-sensitive bovine whey protein; rapidly denatures and aggregates irreversibly between $60\text{--}65^\circ\text{C}$ (lowest heat stability).
• Bovine Serum Albumin, BSA (C): Denatures at $64\text{--}68^\circ\text{C}$.
• $\beta$-Lactoglobulin (D): Denatures at $70\text{--}78^\circ\text{C}$, exposing its free cysteine thiol group and forming irreversible intermolecular aggregates.
• $\alpha$-Lactalbumin (A): Possesses an apparent unfolding temperature around $62\text{--}65^\circ\text{C}$, but because its four disulfide bonds and bound $Ca^{2+}$ ion allow remarkable reversible renaturation upon cooling, it resists permanent loss of solubility better than all other major whey proteins (highest heat stability).