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

In statistical microbiological sampling plans (two-class and three-class plans) established by ICMSF and adopted by FSSAI:

• $n$: The number of sample units chosen independently and at random from a lot that must be examined.
• $m$: The threshold limit; in a three-class plan, values $\le m$ represent satisfactory quality, while values above $m$ but $\le M$ are marginally acceptable.
• $M$: The maximum limit separating marginally acceptable from unacceptable quality.
• $c$: The maximum allowable number of sample units yielding values between $m$ and $M$.
  
  Option analysis:
• The number of sample units from a lot that must be examined to satisfy a given sampling plan: Correct definition of $n$.
• The maximum number or level of relevant bacteria per gram: Incorrect, this defines $m$.
• The maximum allowable number of sample units that may exceed the criterion: Incorrect, this defines $c$.
• quantity used to separate marginally acceptable from unacceptable: Incorrect, this defines $M$.

Lactobacilli are grouped into three physiological fermentation classes:

• Obligately homofermentative (Group I): Ferment hexoses exclusively to lactic acid via EMP pathway, unable to ferment pentoses (e.g. Lactobacillus helveticus, Lactobacillus acidophilus, Lactobacillus delbrueckii).
• Facultatively heterofermentative (Group II): Ferment hexoses to lactic acid via EMP pathway, but also possess phosphoketolase to ferment pentoses into lactic acid and acetic acid (e.g. Lacticaseibacillus casei, Lacticaseibacillus paracasei, Lactiplantibacillus plantarum).
• Obligately heterofermentative (Group III): Ferment hexoses and pentoses via the phosphoketolase pathway producing lactic acid, ethanol/acetic acid, and $CO_2$ (e.g. Limosilactobacillus fermentum, Levilactobacillus brevis).
  
  Option analysis:
• Lactobacillus helveticus: Obligately homofermentative.
• Limosilactobacillus fermentum: Obligately heterofermentative.
• Levilactobacillus brevis: Obligately heterofermentative.
• Lacticaseibacillus casei: Correct. A facultatively heterofermentative lactic acid bacterium.

In dairy fermentations (butter, dahi, buttermilk):

• Statement (I) is true: Citrate-fermenting bacteria (such as Lactococcus lactis subsp. lactis biovar diacetylactis and Leuconostoc mesenteroides) metabolize citrate into pyruvate, which condenses with active acetaldehyde to form alpha-acetolactate. Alpha-acetolactate undergoes non-enzymatic, spontaneous oxidative decarboxylation in the presence of oxygen to form diacetyl, the premier butter aroma compound.
• Statement (II) is true: This oxidative decarboxylation of alpha-acetolactate to diacetyl is a purely chemical (non-enzymatic) process that is strongly catalyzed by low pH and accelerated in the presence of lactic acid accumulated by the acid-producing starter culture.
  
  Option analysis:
• Both Statement (I) and Statement (II) are true: Correct.
• Both Statement (I) and Statement (II) are false: Incorrect.
• Statement (I) is true but Statement (II) is false: Incorrect.
• Statement (I) is false but Statement (II) is true: Incorrect.

Delvotest is a standard broad-spectrum microbial inhibitor ampoule/plate test utilizing Geobacillus stearothermophilus var. calidolactis as the indicator organism:

• Statement (I) is false: Delvotest-SP is specifically sensitive to and designed for beta-lactams (penicillins) and sulfonamides. It has very poor sensitivity for aminoglycosides such as Streptomycin (detection limit is far too high to detect regulatory levels of streptomycin). Hence, claiming it is used for Streptomycin is technically false.
• Statement (II) is true: Delvotest is universally accepted as a standard reference diffusion test for detecting penicillin and beta-lactam residues in herd and silo milk.
  
  Option analysis:
• Both Statement (I) and Statement (II) are true: Incorrect.
• Both Statement (I) and Statement (II) are false: Incorrect.
• Statement (I) is true but Statement (II) is false: Incorrect.
• Statement (I) is false but Statement (II) is true: Correct answer.

Managing bacteriophage contamination in cheese production:

• Statement (I) is false: Phage rotation is an effective preventive strategy to minimize the build-up of specific virulent phages, but it cannot 'completely eliminate' phage growth, because new virulent mutant phages emerge and environmental contamination persists.
• Statement (II) is true: In commercial cheese factories, defined strain starter rotations are routinely implemented on a daily basis or from vat-to-vat during continuous operation to prevent phage amplification.
  
  Option analysis:
• Both Statement (I) and Statement (II) are true: Incorrect.
• Both Statement (I) and Statement (II) are false: Incorrect.
• Statement (I) is true but Statement (II) is false: Incorrect.
• Statement (I) is false but Statement (II) is true: Correct.