ICAR AIEEA PG Dairy Technology 14 July 2023 Shift-1 Paper

Body and textural defects in butter and their technological causes:

• Crumbly body: Caused by a high proportion of high-melting saturated fatty acids ('hard fat', typical of winter milk fat) with insufficient liquid fat to bind grains: (A)-(II).
• Greasy texture: Caused by excessive mechanical working (over-working) or working at elevated temperatures, which completely crushes fat globules and smears excessive liquid oil: (B)-(IV).
• Leaky butter: Caused by insufficient working (under-working), leaving moisture droplets large, poorly dispersed, and visible on the surface: (C)-(I).
• Gritty defect: Caused by undissolved salt grains due to improper or incomplete salting, low moisture, or coarse salt crystals: (D)-(III).
  
  Option analysis:
• (IV), (B)-(III), (C)-(I), (D)-(II): Incorrect.
• (II), (B)-(IV), (C)-(I), (D)-(III): Correct matching.
• (I), (B)-(II), (C)-(IV), (D)-(III): Incorrect.
• (IV), (B)-(I), (C)-(III), (D)-(II): Incorrect.

Physiology of Penicillium roqueforti in blue cheeses (Roquefort, Stilton, Gorgonzola):

• Statement (I) is correct: P. roqueforti acts as the essential secondary ripening flora, growing inside the pierced air channels throughout the interior of blue-veined cheese.
• Statement (II) is correct: It exhibits vigorous lipolytic activity, hydrolyzing milk fat into free fatty acids and beta-oxidizing them into methyl ketones (notably 2-heptanone and 2-nonanone), which provide the classic sharp, peppery aroma and piquant flavor of blue cheese.
• Statement (III) is incorrect: P. roqueforti is uniquely psychrotolerant (grows efficiently at cold cave temperatures of $8\text{ to }12^\circ\text{C}$) and halotolerant (readily tolerates high salt levels up to $4\%$ to $6\%\text{ NaCl}$). Thus, stating that it cannot grow at low temperature and high salt is false.

Mechanisms of mutual proto-cooperation in yogurt starter cultures:

• Role of L. bulgaricus: Possesses cell-envelope bound proteinase (PrtB) that hydrolyzes casein into oligopeptides and free amino acids (notably glycine, histidine, valine, and leucine), which strongly stimulates the growth of the proteolytic-deficient S. thermophilus: Statement (A) is correct.
• Role of S. thermophilus: Metabolizes lactose into lactic acid, formic acid (formate), and carbon dioxide ($CO_2$). Formic acid directly stimulates the purine nucleotide synthesis and growth of L. bulgaricus, and $CO_2$ lowers dissolved oxygen to establish favorable anaerobic growth conditions: Statements (C) and (D) are correct.
• Statement (B) is incorrect: Pyruvic acid and formic acid are metabolic products of S. thermophilus that stimulate the lactobacillus, not vice versa.