Scientists have found a way to put Listeria’s growth in a traditional Norwegian product and have improved detection methods.
Rakfisk is made by fermented trout or char in brine. In recent years it has been linked to various outbreaks of Listeria Monocytogenes, as well as botulism cases.
In 2020, two cases of botulism were registered with the suspected source of infection as homemade Rakfisk. Three recent outbreaks of Listeria were reported, including one at the end of 2018 to the beginning of 2019 that caused 13 diseases.
Nofima led a three -year research project, called Safe Rakfisk, aimed at making the product safer.
“We have tested different solutions to brake Listeria during the process and have found two that work well. The first is a so -called protective culture, and the second is a braking salt from the buffered vinegar type, “said Lars Axelsson, senior scientist at Nofima, who led the work.
Support for protective culture
Protective cultures are lactic acid bacteria with activity against unwanted bacteria and are often insulated from food. Buffered vinegar is a liquid or dried product that mainly contains acetic acid and the salts are neutralized.
“We used the protective culture Lyoflora and the inhibiting salt. Interestingly, the effect of Lyoflora was improved by using a small amount of sugar when the fish was placed in the brine. This even resulted in some murder of Listeria, “said Axelsson.
Nofima has conducted surveys and interviews with people who eat Rakfisk.
Most of them did not know that Listeria could be a problem. However, the majority was aware that Rakfisk is associated with risks and that some groups, such as pregnant women, should avoid the product. As long as the taste is as expected, people can accept that the production method is changed if it makes the Rakfisk safer.
The sensory assessors of Nofima tested untreated Rakfisk, Rakfisk treated with inhibiting culture and Rakfisk treated with braking salt. They evaluated different properties with regard to taste, smell and texture. The Rakfisk treated with the bacterial breeding Lyoflora is very similar to the untreated product, while the inhibiting salt drown gave a sharper and sharp taste.
During the Rakfisk festival in Valdres, Nofima scientists performed a sensory test. A total of 220 people tasted the same variants as the professional sensory assessors. Differences were small, but the participants preferred Rakfisk treated with Lyoflora above both untreated and with diladed Rakfisk.
Producers who tested the various treatments were also more satisfied with the use of Lyoflora than Verdad, because the Rakfisk had unchanged quality compared to regular production.
Improved detection
Rakfisk is stored in plastic tubs and producers regularly sampling and analyzing them to prevent polluted products from reaching the market. When a producer Listeria found in a fairly large production batch, scientists could study how Listeria was divided into the tubs and which methods were best for sampling.
The Norwegian veterinary institute worked on this part of the project. The agency discovered that Listeria is not spreading evenly.
“Samples taken from the bottom always contain Listeria when the bacterium was present in the bath, while the upper layers could be completely free from Listeria,” said Taran Skjerdal, senior scientist.
This led to a recommendation to take samples from below. The methodology of the Norwegian veterinary institute suggests the use of extra long pipettes to take the samples or to lower a mesh strip that absorbs brine of all levels.
“We have great confidence that bacterial protective cultures can contribute to even a safer production and now start greater test production to ensure that it offers the same good taste for the fish,” said Nils Noraker at Noraker Gård Og Rakfisk.
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