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Small Amount of Common Preservative Increases Toxins from Harmful
Bacteria in Food, Study Finds

ScienceDaily (June 25, 2010) � In response to consumer demand for more
natural food, the food industry has reduced the amount of preservatives
in food over recent years. A common preservative is acetic acid, which
is used to stop bacterial growth in dressings, sauces, cheese and

However, new research shows that a small amount of acetic acid does not
have the intended effect, but rather the opposite -- it increases the
amount of toxin from the harmful bacteria in the food.

"In my studies I saw that a small amount of acetic acid caused the
bacteria to become stressed, which meant they reacted by producing more
toxin. However, if a large amount of acetic acid is added, as was done
in the past, the acidity is greatly increased and the bacteria do not
survive," explains Nina Wallin Carlquist, Doctor of Philosophy in
Engineering at the Division of Applied Microbiology, Lund University.

She recently defended a thesis on the subject, in which she studied two
of the most common food poisoning bacteria, Staphylococcus aureus and
Campylobacter jejuni.

The Staphylococcus were used in the acetic acid study. A common vehicle
for staphylococcal food poisoning is pork meat. Therefore Nina Wallin
Carlquist also chose to study how these bacteria behave in different
types of pork meat at room temperature: boiled and smoked ham, Serrano
ham and salami. The bacteria could get into the food in the first place
from an infected cut on the finger of the person who has handled the
meat, for example.

Her results show that it only took a few hours for the bacteria to
multiply in the boiled and smoked ham. In the Serrano ham, it took a
week before the number of bacteria increased and on the salami they did
not survive at all.

"A possible explanation is that the bacteria could not survive the
salami's combination of acidity, salt, fat and dryness. However, there
are other bacteria that thrive on salami. The Serrano ham is
manufactured and stored at room temperature over long periods, which
means it is important that the staff have good hygiene so that the
Staphylococcus cannot get a foothold," comments Nina Wallin Carlquist.

A starting point was to study how the bacteria behave in food. This type
of research is otherwise usually carried out in a controlled environment
in laboratories where a pure culture of a certain type of bacteria is

According to Nina Wallin Carlquist this provides far from the whole
picture because the bacteria are affected by other micro-organisms in
the food and also by how much fat, acid and salt the food contains.

"If we know more about what it is in the food that enables the bacteria
to thrive, we can then adapt the composition of the food product and
thereby improve food safety. This is a new way to approach food safety,"
explains Nina Wallin Carlquist.

The other bacterium, Campylobacter jejuni, is becoming the next big
problem after salmonella. Like salmonella, the bacteria occur naturally
in chicken, without harming the host animal.

However, if the contents of the intestines come into contact with the
meat during slaughter, the meat can become infected. If the chicken is
then not properly cooked the consumer may suffer food poisoning.

"It would be best if the chickens did not get infected with these
bacteria to begin with. In my studies I have therefore found out how the
bacteria become established in the intestines. In the long term, these
results could help in the drawing up of guidelines for hygiene
procedures on poultry farms or in developing a vaccine for the animals,"
says Nina Wallin Carlquist.
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The above story is reprinted (with editorial adaptations by ScienceDaily
staff) from materials provided by Lund University.


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