Nitrites in meat products. Can we lower the ingoing amounts?

Sodium nitrite is an additive that is used, among other things, to enable the food-safe storage of meat products. Research into organic meat products has revealed that nitrites can actually be added in smaller quantities than the legally permitted maximum and still remain effective. Based on the lower levels achieved by the Danish meat industry over the past decade, and also taking findings from research by TNO as well as organisations in 12 other Member States into account, the European Commission is preparing a new directive for the use of nitrites in the manufacture of meat products.

Nitrite is an important additive in processed meat products. It ensures the stable pink colour which consumers expect, the characteristic ‘meaty’ flavour and above all it creates microbiological stability. The use of nitrites in the manufacture of meat products has been a topic of discussion since the 1970s, mainly because of the role of nitrites in the formation of possibly carcinogenic N-nitroso compounds, which can be formed in meat products but also, under certain circumstances, in the human body.

Legislation

Legislation regulates the permitted level of nitrites (Commission Regulation (EC) No. 1333/2008 and Commission Regulation (EU) No. 601/2014) and this has steered the discussion into calmer waters. Recently, however, the nitrite discussion was reignited by a publication by the World Health Organization (WHO) on the health risks associated with the consumption of processed meat. This article explores the function of nitrites in the manufacture of meat products.

Highly reactive and even toxic

Pure nitrite is highly reactive and even toxic in sufficiently high quantities. The nitrite used by the food industry is always mixed with salt in a concentration of between 0.6 and 0.9% to form sodium nitrite. For humans, the lethal oral dose is between 33 and 220mg/kg of body weight. After ingestion and when it comes into contact with blood, the nitrite oxidises the haemoglobin in the blood to the methemoglobin form. This considerably restricts the transport of oxygen from the lungs to other tissue cells. Nitrite also inhibits the functioning of certain enzymes, including those necessary for tissue respiration. The FAO/WHO set the Acceptable Daily Intake (ADI) for nitrite at 0.06mg/kg of body weight. The average daily intake of nitrite is estimated at 2.3mg (NL) which is equivalent to 0.038mg/kg of body weight. The average nitrite content of the meat products on the Dutch market is 12.1mg/kg of product.

Functions

The preservative effect of nitrite in meat products has been studied extensively but still not completely clarified. Because the vegetative microorganisms are deactivated by conventional heat treatments for meat products, the most important factor is the inhibition of heat-resistant bacterial spores such as Clostridium botulinum. Many experiments have been carried out using cultivation media* and meat-containing model systems also stored at ambient temperature to study the effect of nitrite on the inhibition of C. botulinum. Research has demonstrated that the presence of nitrite reduces the chance of toxin formation by a factor of 10 to 100 (1 to 2 log units) (Hauschild et al., 1982; Lücke and Roberts 1993). Own TNO research has verified these findings. Experiments conducted under cooled storage conditions have also demonstrated that no toxins are formed.

In summary: the anti C. botulinum properties of nitrite are multifactorial, primarily concerning interaction between nitrite and other factors such as salt content, aw, pH, additives, intensity with which heat is applied and the presence of quantities of spores. Depending on the product composition, processing and storage conditions, the quantity of nitrite used in the manufacture of meat products can be reduced compared with the legally permitted level.

Colouration

It is thanks to nitrite (nitrogen oxide) reacting with the protein myoglobin that meat products are a pink colour. In the presence of nitrite, myoglobin is first oxi¬dised into metmyoglobin which eliminates the red colour. The nitrite is then reduced to nitrogen oxide (NO) and nitro¬somet¬myoglobin is formed. Effective conversion of myoglobin into nitrosomyoglobin requires a nitrite content of at least 50mg/kg. Own research has demonstrated that at a lower concentration the colouration is still suffici¬ent but the colour stability is not. When heated, the nitrosometmyoglobin is converted into the pink-red nitrosomyochromogen. Although this is a relatively stable form it is converted into metmyochromogen under the influence of oxygen combined with light. Metmyochromogen is brown in colour. In the manufacture of dried sausages or dry-salted meat products, nitrosometmyoglobin (brown) is formed first but subsequent oxidation and fermentation result in a more stable red colour of the meat nitrosomyoglobin.

Replacement?

One way of avoiding having to declare nitrites on the food label is to add a vegetable extract (or vegetable extract concentrate) as a nitrite replacement. This adds a large quantity of nitrate to the product. Reduction and fermentation convert that nitrate into the nitrite form. However, in practice it has been found that in some cases this results in a higher concentration of nitrite in the end product than the legally permitted quantity of added nitrite. In my opinion, therefore, this cannot be called a ‘nitrite replacement’.  

Alternatives

Since the 1980s extensive research has been conducted into opportunities for replacing nitrite in meat products, and in recent decades the effect of a reduction in the addition of nitrite has also been investigated. From these studies, it can be concluded that there are (so far) no alternatives that achieve the same microbiological stability as the current use of nitrite. However, there are extremely promising research findings for the additional use of polyphenols in conjunction with a very low nitrite level in meat products. As colour-forming or stabilising additives, these antioxidants can be combined with herbs and spices that introduce colour. However, high doses are required which can alter the flavour.

Conclusion

Research has demonstrated that the current maximum level of nitrite can be reduced in the manufacture of various meat products. This will further lower consumer exposure to nitrite and hence the possible formation of N-nitroso compounds via meat products.

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* Petri dishes with a certain media, selectively for the cultivation of particular microorganisms/cultures.