New conservation methods increase risk of food poisoning

Development of new, minimally processed food products challenges traditional concepts of food safety

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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 pickles. New research shows, however, 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, PhD in Engineering at the Division of Applied Microbiology of Sweden's Lund University. Dr Carlquist 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 Staphylococci were used in the acetic acid study. A common vehicle for staphylococcal food poisoning is pork meat. 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. Dr Carlquist therefore 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. 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," she comments. Microbial behaviour 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 studied. According to Dr 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," she explains. In her study Dr Carlquist further says: "A greater understanding of how bacterial growth and virulence expression are related and regulated by environmental factors and food preservatives will provide safer food products and give rise to new approaches to disease prevention and control in the future through the improvement of quantitative risk assessments. The virulence of foodborne pathogens can be an important complement to the viable counts traditionally used in food safety assessments." The other bacterium, Campylobacter jejuni, is becoming just as big a problem as Salmonella. Like Salmonella, the bacteria occur naturally in chicken, without harming the host animal. If the contents of the intestines come into contact with the meat during slaughter, however, the meat can become infected. If the chicken is then not properly cooked following infection, then 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 founAir Huarache Classic