When we talk about nitrate in terms of food, it’s the salt potassium nitrate (saltpetre or saltpeter) we are referring to; potassium nitrate is commonly used to cure ham, bacon, sausages and salami. This stops the highly toxic Clostridium botulinum (the bacterium that can cause the rare but deadly botulism) and other nasties from developing.
In fact, certain salt-tolerant microorganisms transform a small portion of nitrate into nitrite: it’s the nitrite that not only acts as a preservative but this bacterial action also allows the distinctive flavour to develop in cured hams.
Nitrites react in the meat to form nitric oxide (NO), which binds to the iron atom in the red pigment myoglobin so in turn preventing the iron from causing the fat to oxidise. (That binding also produces the rosy pink-red color of cured meats.)
Nitric oxide helps regulate blood pressure by signalling arteries to expand; it also signals immune cells to kill bacteria, and helps brain cells communicate with one another. A lack of nitric oxide production in our bodies can lead to hypertension, atherosclerosis, and thrombosis, all of which can result in heart attack and stroke.
Once it was discovered that nitrites and not nitrates were responsible for stopping the food going off, food manufacturers were able to use nitrites straight away rather than potassium nitrate in anything other than hams that were meant to be aged.
Nitrates are already in our diet
The level of nitrates/nitrites in cured meats is not only lower than it used to be, but – and here’s the kicker – you get far higher levels in your saliva, and you swallow that happily! It turns out some bacteria in our mouths turn salivary nitrates into nitrites… and these account for at least 90% of the nitrites we take in. These nitrites seem to help protect us against foodborne pathogens and stomach problems.
Vegetables also contain nitrates! The highest amounts are found in beetroot (red beets), spinach, radishes, celery, lettuce, cabbage, fennel, broccoli, cucumbers, and leeks.
In fact, if you look at packets of cured meats that say ‘no nitrates or nitrites added’ (note, not ‘nitrate-free’), they will probably be cured with nitrate-rich celery powder or celery juice; the nitrates are converted to nitrite by a bacterial culture.
Do nitrates cause cancer?
In large enough amounts nitrates are indeed toxic (so is water!), with the main effect being the development of the rare methemoglobinaemia*, and this condition is reversible.
What of cancer? Do nitrates in meats cause it? The potential of nitrate/nitrite to form carcinogenic N-nitrosamines in cured meats was first identified in 1971. However, their formation can take place only where:
- secondary amines are present
- nitrite is available to react
- pH is near neutral found
- product temperatures reach greater than 130C (such as during the frying of bacon)
Nonetheless, following these discoveries, new regulations and practices came into being. Among those practices was the addition of ascorbic acid (vitamin C, sodium ascorbate, erythorbic acid or sodium erythorbate); ascorbic acid inhibits the chemical reaction that can lead to the formation of nitrosamines**.
In bacon, nitrate is not now permitted, so concentrations of nitrite can be more precisely controlled. Bacon must also have either 550 parts per million added sodium erythorbate or sodium ascorbate, regardless of curing method; this inhibits the potential for nitrosamine formation during frying.
* Methemoglobinaemia (or methemoglobinemia) is a blood disorder in which an abnormal amount of methemoglobin – a form of haemoglobin – is produced. With this condition, the hemoglobin can carry oxygen but is unable to release it effectively to the body tissues which need it. This condition can be inherited or congenital, or caused by exposure to certain drugs, chemicals or foods.
** Amines are organic compounds that contain nitrogen. Nitrosamines are amines substituted by a nitroso (NO) group; can be formed by direct combinationof an amine and nitrous acid (and can even be formed from nitrites in the acidic gastric juice). Some nitrosamines are mutagenic and/or carcinogenic.