Psychrotrophic bacteria seem to be becoming the newest thorn in
the side of the dairy industry. Scary bit is that we are helping
them along.
"How?" do you ask?
Because of economic factors the pre-processing time of raw milk
has been extended to an average of 4 days. This allows ample
time for psychrotrophic, proteolytic bacteria to grow, and form
heat stable enzymes. Although the psychrotrophic bacteria are
easily killed off by normal pasteurization temperatures, the
formed enzymes can survive UHT processes.
This causes multiple problems and we here at Elsenburg Dairy Lab
have especially seen those problems on products like cottage
cheese and UHT milk, more so over the past few years. This is a
group of bacteria that actually loves the cold chain, as it
helps them outwit, outlast and outperform their competition.
Nowadays psychotropic bacteria predominate in raw milk in the
cold chain, especially Pseudomonas spp.
So much so that when the same milk is plated out and incubated
at 7° C and at 30° C(as in Total Plate Count), the psychotropic
growth will overtake the mesophilic growth, causing
psychrotrophic counts to be higher than total plate counts.
I don't think the methods of analysis are of much importance in
this article, because there are many, ranging from
microbial(determining the bacteria) and biochemical(determining
the formed enzyme). Qualitative tests are of no use as we want
to be able to enumerate the psychrotrophic bacteria.
The main concern I have is to raise awareness of a fast growing
problem, that will only become more so in the future.
Possible solutions are the following:
1) Ask your lab to do a monthly psychrotrophic count on all
farmers. This will identify your high risk milk supply.
2) Thermising the milk to 68° C before cooling on the farm. This
would have to be done with a plate heat exchanger, but would be
economical at this stage, because the milk is already at body
temperature(37° C) and the treated milk can run against the
incoming milk to heat it and to be cooled down itself. An ice
bank would also be needed to finish the cooling process. The
thermising process would obviously increase the overall quality
of the milk as well, without influencing heat stability to a
large degree.
3) Very rapid cooling on the farm to 2° C, instead of the usual
4° C and keeping it there until processing.
4) Using a pre-cooler at the factory to cool the milk down
quickly from the 5-7 °C that it arrives at, to 2 °C.
About the author:
Leon the Milkman is the owner of www.LeontheMilkman.com and www.dairy-info.org from where he gives a dairy dictionary and cheese tasting terms guide to new members.
