Food Chemistry of Nitrates, Nitrites, and Cured Meat

Nitrates and nitrites have recently come under fire for their link to colorectal cancer. However, these curing agents are critical in keeping processed meats safe, as well as developing the characteristic flavors and colors we know and love. So, should you stop eating bacon?

Nitrate vs. Nitrite

Nitrates are molecules made up of nitrogen and oxygen. They are found naturally in soil and water and are important in the nitrogen cycle. Nitrites form via the breakdown of nitrates; an oxygen molecule is lost. Our bodies also produce nitrate from the protein L-arginine.

Nitrite is now known to be the chemical agent that drives the curing process, rather than nitrate. Not only does nitrite produce the characteristic flavors and pink color of processed meats, it also preserves the product. This extends shelf-life and keeps the product safe from deadly bacteria such as Clostridium botulinum.

In the diet

In addition to processed meats such as bacon, sausage, and deli-meats, nitrates and nitrites are found in the soil. Therefore, fruits, vegetables, and grains naturally contain nitrates. Vegetables actually contribute the largest amount of nitrates to our diet.

It is also possible that nitrates may enter drinking water through contamination.

cured meat
Deli counter at an open-air market in Toulouse, France

Processed Meats vs Red Meat

“Red meat refers to all mammalian muscle meat, including, beef, veal, pork, lamb, mutton, horse, and goat.”

“Processed meat refers to meat that has been transformed through salting, curing, fermentation, smoking, or other processes to enhance flavour or improve preservation.”

World Health Organization

History of cured meat

You may not realize it, but humans have been curing meat for thousands of years. Salting and smoking were developed to allow storage of excess meat for use throughout the year. Salt was rubbed on the meat and allowed to “cure.” Actually, nitrates were naturally present in the salts used in curing and played a large role in the process, unbeknownst to the butchers of yore.

Video by Institute of Food Technologists

How is meat cured?

There are three types of curing. Chemical curing with nitrates and nitrites, smoking and dehydration. Products may go through one or all three methods. For example, bacon is both chemically cured and smoked. It may also be dried. Pancetta, on the other hand, is chemically cured and dehydrated. Sausages may only be chemically cured.

There are multiple methods for application of chemical curing agents. In dry curing, the agent is applied to the surface of the meat. Alternatively, the curing agents may be dissolved in water as a brine in immersion curing. Nitrates and nitrites may also be injected into the meat through pumping or needling. Injection results in a more uniform distribution and decreases curing time.

Chemistry of curing

Nitrates, in the form of sodium nitrate or potassium nitrate, are reduced to nitrites by bacteria. Today, sodium nitrites are primarily used because we know nitrites are responsible for the important reactions in curing. This helps to better control the process.

Further reduction in curing leads to the production of nitric oxide. Nitric oxide then combines with myoglobin present in the meat to form nitrosylmyoglobin. When heated, nitrosohemochrome forms, which is the pigment responsible for the characteristic pink hue of cured meats. It also produces important flavor compounds. Nitrites act as antioxidants, which prevent oxidative rancidity of the fat in the meat. They also bind water and prevent the growth of dangerous microbes.

Plate of Bacon

Other ingredients are also used in the curing process. Sugar is important because it counteracts the harsh flavor of large amounts of salt. Ascorbate (Vitamin C), used in the form of sodium ascorbate or sodium erythorbate, are used to speed up the reduction of nitrates to nitrites. They also stabilize the pink color. Phosphates may also be used in liquid cures to increase water holding capacity and improve yield. Take a look at the label of your favorite processed meat to get an idea of which ingredients are used.

The myth of “nitrate-free” products

Sorry to burst your bubble, but nitrate-free foods really aren’t free of nitrates. As I mentioned above, nitrates are found abundantly in plants. Most nitrate-free products still contain nitrates from natural sources, such as celery. The nitrites from this natural source may also randomly change in the body to create the same carcinogenic compounds as synthetic nitrates/nitrites. Your body can’t tell the difference. Look for celery powder on the label.

Health

Red meat meats have long been associated with an increased risk of diabetes, heart disease, and stroke. Nitrites in processed meats have recently been linked to colorectal cancer, pancreatic cancer, and prostate cancer.

In 2015, the World Health Organization (WHO) reviewed more than 800 epidemiological studies and concluded that red meat is a class 2A carcinogen, meaning there is evidence it is likely to cause cancer. Processed meats are class 1, meaning there is sufficient evidence to
conclude they are carcinogenic. This group also includes products such as alcohol, tobacco, and asbestos. Understandably, many people were concerned and the media added to the flurry with sensationalized headlines.

Risk vs. Likelihood

As pointed out in a report from the Harvard T. Chan School of Public Health, the WHO findings do not assess the degree of risk. You’d want to know, right, if something increased your risk of cancer by say, 1% versus 60%? Educated risk is what life is all about.

It was found that the more processed meat consumed, the higher the degree of risk. Roughly 34,000 deaths are attributed to diets high in processed meats each year. However, to put it in perspective, the overall risk of smoking is 2000% higher than that of consuming processed meats and results in 1 million deaths each year. So, even though they are in the same category, the risk factor is not the same.

In the body

It is believed nitrates are not of concern to human health and the majority are excreted in the urine. However, bacteria in saliva convert dietary nitrates to nitrites. Nitrites may go on to form small amounts of toxins in the body including methemoglobin, which reduces oxygen transport, or nitrosamines, which are known carcinogens. The proteins and heme in meat may facilitate these changes.

However, nitrites may also form nitric oxide, which is important for human health. According to Nathan Bryan, an expert on nitric oxide and health, this chemical is important for regulating blood pressure, keeps blood vessels healthy, and plays a role in destroying cancer cells. Vitamin C and polyphenols present in vegetables are thought to induce the formation of nitric oxide versus nitrosamines, as compared to processed meats. Interestingly, Bryan says, traditional vegetables are higher in nitrates than organic vegetables.

What role does cooking play?

Cooking meat at high temperatures and in direct contact with heat facilitates the formation of carcinogenic compounds, such as polycyclic aromatic hydrocarbons and heterocyclic aromatic amines. However, there is not enough evidence to conclude that cooking method is associated with cancer risk.

Regulations

Nitrates and nitrites can be dangerous when consumed in large amounts. Therefore, the USDA mandates that nitrites be present at < 200 ppm in finished meat products. The European Food Safety Authority completed research in 2017 and affirmed the current recommendations are safe for human health.

“The current acceptable daily intake (ADI) for nitrates is 3.7 milligrams per kilogram of body weight per day (mg/kg bw/day). The safe level for nitrites was re-established at 0.07 mg/kg bw/day, close to the slightly more conservative existing ADI of 0.06 mg/kg bw/day.”

European Food Safety Authority

Regulations involving “nitrate-free” products made with celery salt are less clear.

What does it all mean?

Meat is an important source of complete protein in the diet. It also provides other important nutrients, such as Vitamin B12 and iron. However, red meat and processed meats are also high in saturated fats and salt. There is evidence that consuming red or processed meat increases your risk of cancer. Although, the degree of risk is very small as compared to other carcinogens.

Limiting your intake of red meat and processed meat means you can still enjoy your favorite foods responsibly. Be sure to eat only one portion size at meals and consume only on occasion. For reference, a portion of meat is roughly equal to the size of a deck of cards. Or, try substituting with poultry or vegetable proteins such as chickpeas or beans.

It’s important to remember that advances in technology keep food safe and allow us to store resources so we don’t have to spend the majority of our time cultivating food. Nitrates and nitrites keep you safe from harmful bacteria in cured meat and produce delicious flavors. Understanding ingredient functionality, along with the associated health risks, can help us make more informed decisions.


References

Code of Federal Regulations. 2018. Title 21, Volume 3 21CFR172.175

European Food Safety Authority. 2017. EFSA Confirms Safe Levels for Nitrates and Nitrites added to Foods. https://www.efsa.europa.eu/en/press/news/170615-0

Harvard T. Chan School of Public Health. 2015. WHO report says eating processed meat is carcinogenic: Understanding the findings. https://www.hsph.harvard.edu/nutritionsource/2015/11/03/report-says-eating-processed-meat-is-carcinogenic-understanding-the-findings/

Lopez-Alt, JK. 2015. The Food Lab. WW Norton & Co, Inc. New York, NY. pp494-495.

Ray, FK. Meat Curing. Oklahoma State University. Oklahoma Cooperative Extension Service.http://factsheets.okstate.edu/

Tarver, T. 2019. Are nitrates and nitrites misunderstood? Food Technology. 73:1. pp43-45.

World Health Organization. 2015. Q&A on the carcinogenicity of the consumption of red meat and processed meat. https://www.who.int/features/qa/cancer-red-meat/en/

Disclaimer: This post is for informational purposes and is not meant to provide health advice

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