Researchers, including ones from Nofima, have tested numerous measures in order to discover the most effective remedies for removing the unwanted bacteria, and mild heat treatment (at roughly 43 °C) proved to be a method that both makes sausages safer and maintains their high quality.
“Heat treatment is a robust method and provides an effective reduction,” says Research Scientist Even Heir at Nofima. “But of course, the effect hinges on the combination of duration and temperature. The higher the temperature and the longer the duration, the better the effect. However, this might also affect the taste and other sensory properties. Furthermore, any heat treatment must be implementable in industrial processes.”
Several ways to make cured sausages safer
In addition to heat treatment, the researchers examined how high pressure, storage, freezing/thawing, and changes in the recipe and productions process affect the E. coli bacteria in cured sausages.
The results show that several of the measures do have an effect. Neither the use of salt and nitrite in the recipe nor freezing/thawing the end products have much of an effect by themselves, though they can be effective in combination with for example a storage phase. Storage temperature is significant, and E. coli is more effectively reduced at room temperature than at refrigerator temperature.
For its part, high pressure processing of cured sausage is an effective method against unwanted bacteria, but the greatest barrier to this method is probably high investment costs and implementing the technology in production.
Knut Framstad, the Director of Food Safety at Nortura, says that for Nortura it has been important to study hygienic measures as well. They concluded that although good slaughter hygiene and cleaner animals are an advantage, they are insufficient in themselves.
The taste should remain the same
At the same time that the cured sausages must be safe, neither the taste nor other sensory properties should change. An important part of the project has therefore been to track the development of the sensory properties. It turns out that both heat treatment and increased salt content can result in unwanted changes in the sensory properties. Conversely, other measures such as high pressure and storage have little effect on sensory aspects.
The relationship between the sensory properties and temperature depends largely on the extent of the temperature increase and the duration of the heat treatment.
“Our tests show that 43-degree heat treatment for 24 hours has a good effect, with minimal sensory alterations,” says Even Heir. “But it should be up to the individual producer to test out the documented methods on their own products, with regard to the extent to which sensory properties are altered, depending on duration and temperature. Increasing the salt and nitrite content seems out of the question, nor would it have much of an effect. However, different combinations can have effects that in tandem make sausages safer without having a detrimental effect on sensory quality.”
Pathogenic E. coli bacteria require special measures
The reason for the comprehensive research on E. coli bacteria in particular is that certain types of E. coli bacteria can cause severe damage in far lower quantities than what is normal for other bacteria. Even though most types of E. coli bacteria are harmless, as few as 10-100 EHEC (enterohemorrhagic E. coli) bacteria can cause serious infections that may result in kidney failure and death.
The intestines of ruminants are an important reservoir for EHEC, and considering that occurrences of these bacteria seem to be increasing, more knowledge is important.
“In this project we have worked on optimizing the production of cured sausage so that unwanted bacteria can be avoided in the finished sausages,” Even Heir concludes.
The project is financed by the Research Council of Norway, the Foundation for Research Levy on Agricultural Products, the Agricultural Agreement Research Fund, and the meat industry. The project commenced January 2007 and concluded 31 December 2010.