Under refrigerated conditions, Gram-negative rods that are able

to produce under such conditions ( psychrotrophic/cold-loving

bacteria ) usually predominate, especially Pseudomonas spp.

This is especially so when the milk has a high initial infection

of these bacteria and the milk is stored for 2-4 days before

pasteurization – which is often the case these days, where milk

is mostly being picked up from farms every second day only.

This deterioration also often influences the final products made

from such milk, because although bacteria will mostly be killed

by pasteurization, some produce exo-enzymes that survive

pasteurization and even the UHT (Ultra High Temperature/Long

Life) process in some cases.

An example of Pseudomonas attacking dairy products happen a lot

with cottage cheese. Pseudomonades are widely distributed and

aerobic. They tend not to need much carbohydrate, which help

them a lot in attacking cottage cheese, because most of the

lactose has been removed in the cheese making process. They live

very well on high-protein foods like cottage cheese producing

slime, pigments and odours. They also prefer high water activity

( high moisture), which makes cottage cheese pretty much the

ideal food considering everything that has been said.

Many Pseudomonas spp. are psychrotrophic ( cold-loving )

bacteria although they will grow a lot faster from 15 degrees

Celsius to temperate.

Thus a temperature shock during transport for example will give

them a big boost – to cause even more destruction.