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Pseudomonas in Cottage Cheese and Dairy

Under refrigerated conditions, Gram-negative rods that are ableto produce under such conditions ( psychrotrophic/cold-lovingbacteria ) usually predominate, especially Pseudomonas spp.

This is especially so when the milk has a high initial infectionof these bacteria and the milk is stored for 2-4 days beforepasteurization - which is often the case these days, where milkis mostly being picked up from farms every second day only.

This deterioration also often influences the final products madefrom such milk, because although bacteria will mostly be killedby pasteurization, some produce exo-enzymes that survivepasteurization and even the UHT (Ultra High Temperature/LongLife) process in some cases.

An example of Pseudomonas attacking dairy products happen a lotwith cottage cheese. Pseudomonades are widely distributed andaerobic. They tend not to need much carbohydrate, which helpthem a lot in attacking cottage cheese, because most of thelactose has been removed in the cheese making process. They livevery well on high-protein foods like cottage cheese producingslime, pigments and odours. They also prefer high water activity( high moisture), which makes cottage cheese pretty much theideal food considering everything that has been said.

Many Pseudomonas spp. are psychrotrophic ( cold-loving )bacteria although they will grow a lot faster from 15 degreesCelsius to temperate.

Thus a temperature shock during transport for example will givethem a big boost - to cause even more destruction.

About the author:
Leon the Milkman is the owner of and from where he gives a dairy dictionary and cheese tasting terms guide to new members.