Listeria in Estonia was most often found in cold-smoked and lightly salted fish — ERR News
In Estonia, the bacterium Listeria monocytogenes was most often detected in ready-to-eat fish products, primarily in lightly salted and cold-smoked fish. These conclusions were reached by Julia Koskari in her doctoral dissertation defended at the Estonian University of Life Sciences, ERR News reports.
The researcher analyzed more than 30,000 samples of ready-to-eat products from 2012 to 2016. Meat, fish, dairy, prepared foods and bakery products, fruit and vegetable products, mixed salads, and other categories were studied. Listeria was detected in 3.6% of all samples tested using the bacterial detection method.
The highest share of positive samples was in fish
Among fish products, 11.6% of samples tested positive for L. monocytogenes. The share was particularly high among lightly salted and cold-smoked fish. The bacterium was recorded much less frequently in hot-smoked and heat-treated fish products, while it was not detected in canned fish.
In salads, ready meals, and fruit and vegetable products, the share of positive samples ranged from 2.1% to 3.9%. In bakery and dairy products, the figure stood at 0.2–0.5%. Listeria was not found in sauces, baby food, or products for special medical purposes.
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The presence of the bacterium does not always mean a hazardous concentration: in 99.3% of samples in which the number of microorganisms was determined, there were fewer than 10 bacteria per gram or the level was below the limit of quantification. At the same time, in a small number of fish, meat, and fruit and vegetable products, the figure exceeded the EU criterion used in the study as a reference point: 100 bacteria per gram or milliliter at the end of the shelf life. In 17 samples, the level exceeded 1,000 bacteria.
Plant additives did not replace safety measures
Another part of the study concerned the use of plant powders as additives in meat products. The tested ingredients included rhubarb, tomatoes, apples, onions, garlic, blackcurrants, chokeberries, and rowan berries. Powder made from rhubarb stalks was the most effective at slowing the growth of aerobic microorganisms, yeasts, and molds.
However, tests on cooked ground-meat products showed that all the products studied allowed listeria to multiply. Rhubarb powder and a combination of rhubarb and tomato only slowed this process but did not stop it. Plant additives can help extend shelf life and curb spoilage, but they are not a universal substitute for heat treatment, contamination prevention, production hygiene, a proper cold chain, and correctly established shelf life.
Listeria monocytogenes can multiply slowly even at refrigerator temperatures. For people in high-risk groups, including older people, pregnant women, and people with weakened immune systems, the study recommends observing storage temperatures and shelf lives and treating cold-smoked and lightly salted fish consumed without heating with caution. The refrigerator temperature is recommended to be maintained at 2–4 degrees Celsius, no higher.
