Q.71
Which of the following statements are true?
(A). Pseudomonas produces heat-labile protease and lipase in milk
(B). Many strains of Pseudomonas are psychrotrophic
(C). Pseudomonas in pasteurized milk may come as a post-processing contaminant
(D). Alcaligenes viscolactis causes "ropiness" in milk
Choose the correct answer from the options given below:
- Microbiology of Pseudomonas in Dairy:
- Heat-Stability of Enzymes: Psychrotrophic Pseudomonas species (e.g., P. fluorescens, P. fragi) produce heat-stable (not heat-labile) extracellular lipases and neutral metalloproteases that survive high-temperature short-time (HTST) pasteurization and ultra-high-temperature (UHT) processing, causing bitterness, gelation, and rancidity [Statement A is FALSE].
- Psychrotrophic Nature: They replicate efficiently at refrigeration temperatures ($4\text{--}7^\circ\text{C}$), dominating raw cold-stored milk flora [Statement B is TRUE].
- Post-Pasteurization Contamination: Because vegetative cells of Pseudomonas are readily destroyed by heat, their presence in pasteurized packaged milk is a classic indicator of post-pasteurization contamination from pipelines, filling valves, or rinse water [Statement C is TRUE].
- Ropiness in Milk: Alcaligenes viscolactis secretes viscous capsular exopolysaccharides under refrigeration, causing stringy/ropy defect in milk [Statement D is TRUE].
Correct option: (4) (B), (C) and (D) only.
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