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Replace sulphur dioxide with organic acids and nisin to cut microbial levels.

The microbiological status of fresh pork sausage is influenced by the quality of the meat and its subsequent handling and processing. When stored aerobically at refrigeration temperatures, the predominant microflora consists of Gram-negative, non-spore-forming rods that spoil the product through putrefaction. In Europe, sulphur dioxide, in the form of sodium metabisulphite, is used to inhibit the microbial spoilage of fresh pork sausage.

But sulphites have been linked to the aggravation of asthmatic and other respiratory conditions, urticaria, angiodema, headache and gastrointestinal dysfunction in some individuals. In the United States, using sulphites in foods that are a source of thiamine, such as fresh red meat, is prohibited.

Scientists at University College Cork (Departments of Food Technology and Microbiology, County Cork, Ireland) examined the preservative effect of sodium lactate, sodium citrate and nisin, used individually and in combination, on fresh pork sausage. The potential of sodium citrate or sodium lactate, used by themselves or in combination with nisin, was assessed in sausage inoculated with S. aureus MMPR 3 and S. kentucky AT 1.

The results indicate that a combination of sodium lactate and nisin was particularly effective in reducing total bacterial counts in this product. It also appears that this combination provides increased protection against common pathogenic contaminants of fresh pork sausage: S. aureus and S. species.

When evaluating the effect of the selected preservatives on the survival of S. aureus in sausages stored at 4 C, researchers found that sulphur dioxide was least effective in controlling the staphylococcal population. Introducing nisin to the sausage caused a dramatic decrease in staphylococcal populations within 24 hr. Further reductions were observed over the test period which, while not as substantial as the initial decrease, were still more substantial than reductions seen with any other treatment.

The differences between the preservative treatments was not as obvious in terms of the control of S. kentucky in the sausage system. All treatments led to a net reduction in salmonellae recovered from the sausage after 10 days. The sulphur dioxide control was the least effective. Only minor differences were observed between treatments consisting of nisin, sodium lactate, sodium citrate and their various combinations. Investigators theorize that the Salmonella numbers were reduced by nisin because the cell walls were damaged by either osmotic (due to the presence of salt or lactate) or cold shock, or by a combined effect of the two. This could have allowed nisin to penetrate into the cell membrane.

Researchers believe that the results of this study indicate that the use of nisin alone or in combination with sodium lactate gives better protection against S. aureus and Salmonella and a longer shelf life. They provide a promising alternative to using sulphite in fresh pork sausage.

Further information. Elke Arendt; phone: +353-21-902064; fax: +353-21-276318; URL:
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Publication:Microbial Update International
Date:Jun 1, 2001
Previous Article:Expanding nisin's applications.
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