The European Commission set new limits for the use of nitrites and nitrates as food additives in 2008. These chemicals are intended to protect against the growth of pathogenic bacteria such as Listeria, Salmonella, and Clostridium botulinum, while the EU limits are aimed at reducing exposure to nitrosamines. We have long used nitrate and nitrite as preservatives in curing meat. Nitrate and nitrite are permitted for use in foods in many countries such as Mainland China, the United States, the European Union, Canada, Australia and New Zealand. The concern is that nitrate can be converted into nitrite in the gut and then form N-nitroso compounds such as nitrosamines, which may cause cancer in humans, though evidence as to whether nitrate or nitrite per se in food can cause cancer in humans is inadequate or limited. We need to be very careful before branding food additives as causing human disease - we can find naturally occurring nitrates and nitrates in water and vegetables, especially in leafy and root vegetables such as lettuce, beets, celery, carrots, and more.
There is a group of people who regard preservatives as being unhealthy and added by unscrupulous manufacturers. They want their food to be “all-natural, with minimal processing and no chemicals”. Apart from the fact that this description is meaningless, it got me thinking about additives and specifically preservatives.
As a first step in preparing this post, I followed standard research principles and surveyed the packaged foods in our kitchen cupboard and read all the ingredient labels - a challenge in itself for anyone with less than 20:20 vision. It came as something of a surprise to find that few of the foods contained anything that I would regard as unnecessary in the food type. Sure, there were acidity regulators and anti-caking agents, salt and the occasional antioxidant, natural colours and flavours, while some of the wines declared sulphur dioxide, but very few specific mentions of the dreaded preservatives. A list of permitted additives can be found on the New Zealand Government food safety website. [1]
From the microbiologist’s point of view, preservatives are added to prevent the growth of pathogens or spoilage organisms during the shelf life, reducing loss and increasing food safety. Acidulants, organic acids and parabens have all been used, but ‘natural alternatives’ are being increasingly used. Many leafy and root vegetables contain nitrate and nitrite and it is estimated that around 80% of the nitrates and nitrites we consume are naturally occurring from the plants we eat. Nitrite may be formed by reduction of nitrate by bacteria in the food.
While I was at Hong Kong University, I co-supervised a PhD student who was studying the use of extracts of traditional Chinese herbs as food preservatives. Several of the papers that came out of that work have been my most heavily cited, and it is clear that there is great interest in these natural chemicals in the preservation of meats and dairy products. However, the potential for reliance on extracts may be limited because of source availability, and synthetic nature-identical versions of the active components may be necessary if natural preservatives are to be used extensively.
Of course, manufacturers will often use chemical additives in conjunction with other preservation processes, such as refrigeration, freeze-drying or UV irradiation. Boiling and addition of sugar, followed by sealing in airtight jars and packages, kills bacteria and prevents their regrowth and recontamination. Canned foods are processed for long-term shelf stability and if the food is “low acid” i.e. with a pH greater than 4.5 and thus able to support the germination and growth of Clostridium botulinum spores, the heat process is designed to reduce the spore count by a factor of 1012, resulting in a sterile product that will keep for years, provided that the can remains sealed.
[1] Identifying Food Additives. ISBN No.: 978-1-99-004303-1 Online). https://www.mpi.govt.nz/dmsdocument/3433/direct
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