ICAR AIEEA PG Dairy Technology 09 July 2023 (Shift 1) Paper

Chemical origin of cooked flavour in heated milk:

• Free amino groups participate in Maillard browning at severe heat treatments to yield pyrazines and furans.
• Cooked flavour in milk heated beyond $74^\circ\text{C}$ originates from the thermal unfolding and denaturation of whey proteins, especially $\beta$-lactoglobulin, which exposes and activates free sulphydryl (-SH) groups, leading to the formation of volatile sulphur compounds such as hydrogen sulphide ($H_2S$).
• Hydroxy groups do not confer cooked sensory characteristics.
• Reducing moieties drive glycosidic reactions rather than characteristic thiol aromas.

Chemical agents for membrane sanitization and cleaning:

• Formaldehyde ($0.1\text{--}0.5\%$) is an established chemical sterilant and storage preserving agent for inactive membrane filtration plants.
• Nitric acid ($HNO_3$, typically $0.5\%$) is an inorganic acid cleaner used in Clean-In-Place (CIP) systems to solubilize mineral scales and calcium phosphate foulants; it is a cleaning descaler, not a membrane sterilant.
• Hypochlorite solution (carefully buffered chlorine) is used as a chemical sanitizing agent for chlorine-resistant membranes.
• Sodium metabisulphite ($0.1\text{--}0.5\%$) is widely used as a storage sterilant and biocide to prevent microbial growth during membrane downtime.

Mechanics of paneer pressing and block formation:

• Assertion (A) is true because after whey drainage, paneer curd must be hooped and pressed under pressure (around $2\text{--}3\text{ kg/cm}^2$) while still hot ($\gt 70^\circ\text{C}$).
• Reason (R) is true because at elevated temperatures, milk fat remains in a completely molten state and the casein network possesses maximum deformability and plasticity, permitting individual curd grains to meld and fuse cohesively into a smooth, sliceable, uniform block without shattering.
• If allowed to cool before pressing, fat crystallizes, casein loses plasticity, and the resulting paneer crumbles and fails to form a solid block; hence Reason (R) is the exact scientific explanation of Assertion (A).
• Thus, Both (A) and (R) are true and (R) is the correct explanation of (A).

Matching dairy thermal processes with temperature/time regimes:

• Pasteurization corresponds to (III) $72^\circ\text{C}$ for $15\text{ sec}$ (standard HTST pasteurization regimen).
• Sterilisation corresponds to (IV) $118^\circ\text{C}$ for $15\text{ min}$ (standard batch retort in-bottle sterilization).
• Homogenisation corresponds to (I) $60^\circ\text{C}$ / no hold (preheating to liquefy fat for effective droplet breakup).
• Bactofugation corresponds to (II) $55\text{--}60^\circ\text{C}$ / no hold (centrifugal spore separation temperature).