Bacillus cereus produces two distinct types of food poisoning syndromes: an emetic syndrome caused by a small, cyclic dodecadepsipeptide toxin called cereulide, which is extremely heat stable ($126^\circ\text{C}$ for $90\text{ minutes}$), and a diarrhoeal syndrome caused by heat-labile protein enterotoxins (such as Hbl, Nhe, and CytK).

Option analysis:

• Undulant fever: Caused by Brucella species (Brucellosis), characterized by undulating pyrexia.
• Abortion: Caused by Brucella abortus, Listeria monocytogenes, or Campylobacter fetus in livestock.
• Diarrhoeal syndrome: Caused by heat-labile enterotoxins of Bacillus cereus produced in the small intestine.
• Emetic syndrome: Correct. Pre-formed heat-stable cereulide toxin in food causes acute vomiting and nausea within $1\text{ to }6\text{ hours}$.

A distinctive 'musty potato' off-flavour in cold-stored milk is caused by the growth of psychrotrophic Gram-negative bacteria, predominantly Pseudomonas taetrolens. These bacteria synthesize alkylated alkoxypyrazines, specifically 2-methoxy-3-isopropylpyrazine, which has an extremely low sensory detection threshold.

Option analysis:

• methoxy-3-isopropylpyrazine: Correct. Compound produced by Pseudomonas taetrolens responsible for the musty potato defect in milk.
• Dimethyl sulphide: Contributes to cowy/barny or cooked milk flavours at low concentrations.
• Diethyl sulphide: Volatile sulfur compound associated with pungent sulfury defects.
• methylbutanol: Compound responsible for the malty off-flavour produced by Lactococcus lactis subsp. lactis biovar maltigenes.

Lactenins are natural antibacterial substances originally discovered in fresh raw milk active against Streptococcus pyogenes. They comprise three distinct fractions: Lactenin 1 ($L_1$, predominantly found in colostrum, identified as agglutinins/antibodies), Lactenin 2 ($L_2$, in normal milk, identified as the lactoperoxidase-thiocyanate system), and Lactenin 3 ($L_3$). Because these three fractions differ significantly in molecular identity, thermal stability, specificity, and mechanism of action, stating that they exhibit similar activity is NOT true.

Option analysis:

• True: Lactoperoxidase system requires oxygen/peroxide and shows minimal or no activity under strictly anaerobic conditions.
• True: Reducing agents (such as cysteine, glutathione, or thiols) reduce the hypothiocyanite and inhibit lactenin activity.
• NOT true (Correct answer): The three lactenins differ markedly in heat resistance, chemical identity, and antimicrobial spectrum.
• True: Lactenins were originally characterized by their potent bacteriostatic action against Streptococcus pyogenes.

In mastitic milk, the permeability of mammary epithelial tight junctions increases, allowing blood sodium and chloride ions to pour into the milk, elevating chloride concentration from normal ($0.08\text{ to }0.12\%$) to $\gt 0.14\%$. The Mohr titration method using standard silver nitrate ($\text{AgNO}_3$) and potassium chromate ($\text{K}_2\text{CrO}_4$) indicator is the classic chemical screening test for mastitic milk.

Option analysis:

• Detection of mastitic milk: Correct. Silver nitrate and potassium chromate are used in chloride estimation for diagnosing mastitis.
• Differentiating faecal and non faecal coliforms: Tested via IMViC tests and elevated temperature incubation ($44.5^\circ\text{C}$ in EC broth).
• Assessing activity of starter cultures: Tested via horner/acid development test using standard sodium hydroxide titration.
• Differentiating Gram positive and Gram negative bacteria: Accomplished using crystal violet, iodine, alcohol, and safranin.

Statement (I) is false: The Moseley keeping quality test is NOT a sterility test; it is a keeping quality and post-pasteurization contamination test for pasteurized fluid milk to predict refrigerated shelf-life.
Statement (II) is false: In the Moseley test, samples are stored at refrigeration temperatures ($7.2^\circ\text{C}$ or $45^\circ\text{F}$, not $30^\circ\text{C}$) for $5\text{ to }7\text{ days}$, after which standard plate count (SPC) is performed at $32^\circ\text{C}$ for $48\text{ hours}$ and compared with the initial day-0 SPC.