New analysis allows prediction of shelf life for pasteurized bottled milk.
At I&A Lab we think that the most important part of a plant is production,
and the laboratory should provide help to production to solve and prevent
the development of quality problems. Production faces different types
of problems like:
1 - Quality of the
raw milk received
2 - Equipment
3 - CIP
4 - Packing material
5 - Personnel
All of these can affect
the quality of the final product and as a consequence the shelf life.
Our analysis is designed for use with pasteurized milk. To establish the
shelf life of bottled milk it is necessary to be able to predict how the
product is going to behave in the stores, at the correct temperature,
and to know what is going to happen if the product is abused. The ideal
is to have this prediction in a reasonable amount of time, the sooner
after the milk is bottled being better.
There are different
groups of microorganisms capable of growing and spoiling the milk, for
our study we consider that the mesophilic (growing between 68° and
113°F), and psychrophilic (growing between 20° and 68°F) are
the most important groups, so we focus our effort on the mesophilic's
which can spoil the milk when it is abused, and the psychrophilic's which
can spoil the milk even at temperatures below 45°F. Most psychrophilic
microorganisms are a result of post - pasteurization contamination, due
to the fact that they usually die with pasteurization. It is known that
milk is an excellent media for the growth of many microorganisms, it is
also known that if the milk is kept under 45°F many microorganisms
stop or decrease their growth.
The legal analysis
for pasteurized bottled milk uses one milliliter of milk in a solid media
for total aerobic counts and coliform counts. It is not a requirement
to analyze psychrophilics, but the most widely used analysis takes 7 to
10 days to complete. The solid media employed is very different from liquid
milk, so much so that it takes 48 hrs to see colonies growing in the solid
media plates, incubated at 113°F, while it takes only a few hours
for the milk to spoil. This means that for most of the microorganisms
it is easier to grow in a liquid than in a solid. The reason for the use
of solid media is to be able to count the amount of colonies per milliliter
of milk.
We have developed
a new method using liquid milk in a volume 10 times higher than normal
in special equipment using new software. This allows us to detect microorganisms
in very low concentrations. We also employ two different medias for psychrophilic
bacteria, along with media for pseudomonas, and mesophilic bacteria. This
allows us to have a wide spectrum of detectable milk inhabiting microorganisms.
We created a database
with our results and compared them against the results of the plated fresh
samples, and the same samples preincubated at 68°F for 16 hrs. Finally,
the milk was flavored over a period of time until it was determined to
be no longer acceptable for consumption.
After more than 8000 samples being analyzed we are able to detect in 20
hrs samples which will have 10 days or less of shelf life. If the milk
is contaminated for any reason we will be able to give the production
plant this information. We are able to report in 24 hrs if the milk has
any problem which may compromise its shelf life.
We will issue a second
report in 48hrs stating the amount of psychrophilic, pseudomonas, coliform,
and mesophilic bacteria in the milk sample, with a prediction, in number
of days, with which the milk will be in good condition if stored at 45°F.
Also, the number of days of shelf life if the milk is kept between 50°
and 55°F will be supplied.
During our study we
found a type of bacteria capable of growing at 68°F. We identified
this as Bacillus megaterium (mesophilic). As its presence occurred frequently
we studied it and determined that even though it is capable of growing
at room temperatures it is not capable of growing below 45°F, however
it grows rapidly if the milk is abused.
As the milk is a biological
product, and there are millions of different microorganisms capable of
growing and making changes in the milk, we will continue our study. In
the future we will be able to provide more information to help production
managers make better decisions regarding the shelf life of their products.
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