Processing of Food Commodities

Assertion (A) is true: Coffee is universally recognized and classified as a central nervous system stimulating beverage. Reason (R) is true: The psychostimulant effect is caused by caffeine (1,3,7-trimethylxanthine), which competitively antagonizes adenosine receptors ($A_1$ and $A_{2A}$) in the brain, preventing drowsiness and increasing alertness. Therefore, Reason (R) is the precise scientific explanation of Assertion (A).

Option analysis:

• Both (A) and (R) are true and (R) is the correct explanation of (A): Correct, caffeine's receptor antagonism directly explains coffee's stimulating nature.
• Both true but not correct explanation: Incorrect, (R) directly explains (A).
• is true but (R) is false: Incorrect, (R) is true.
• is false: Incorrect, (A) is true.

Cooked (cabbage-like or sulfurous) flavor that develops in heated milk (above $74^\circ\text{C}$) is caused by the thermal denaturation of whey proteins, predominantly $\beta$-lactoglobulin and $\alpha$-lactalbumin. Denaturation exposes reactive free sulfhydryl ($-SH$) groups that oxidize into volatile hydrogen sulfide ($H_2S$), dimethyl sulfide, and related volatile sulfur compounds.

Option analysis:

• Heat denaturation of casein: Caseins are heat-stable and do not denature at standard pasteurization temperatures.
• Heat denaturation of lactalbumin: Correct, whey protein denaturation exposes free sulfhydryl groups imparting cooked flavor.
• Caramelization of lactose: Imparts burnt or toffee notes only at severe autoclaving temperatures.
• Hydrolysis of lipids: Causes rancid or soapy off-flavors, not cooked flavor.