Risks and Benefits of Sodium Nitrite in Processed Meats07 June 2013
Curing with nitrite has been used, essentially, for thousands of years to produce safe and nutritious products and to effectively preserve meat, according to research by Jeffrey J. Sindelar and Andrew L. Milkowski from the University of Wisconsin.
Since the controversies about the safety of nitrite that started in the mid-20th century, much has been learned about nitrite and heme chemistry and the overall metabolism of nitrogen oxides in humans.
Research conducted since the mid-1980s has suggested that nitrite is a significant molecule important for human health.
New scientific discoveries are now providing a better understanding of the profound and important roles nitrite plays in normal body functions, the study, Sodium Nitrite in Processed Meat and Poultry Meats: A Review of Curing and Examining the Risk/Benefit of Its Use published by the American Meat Science Association.
Dietary nitrates from vegetable consumption, for example, have been shown to serve as significant sources for the endogenous production of nitrite and nitric oxide in the human body.
Nitrite is considered an essential curing ingredient responsible for ‘fixing’ the characteristic colour associated with cured meats, creating a unique flavour profile that is distinguishable from products not containing nitrite, providing control of the oxidation of lipids, and serving as an effective antimicrobial by itself or synergistically with other ingredients (Sebranek and Fox, 1985; Townsend and Olson, 1987; Pegg, 2004).
Nitrate, also considered a curing ingredient, is only effective in the same manner as nitrite if first reduced to nitrite.
This reduction can be accomplished by either naturally present bacteria on the meat or by the addition of bacteria possessing nitrate reductase activity (Gray et al., 1981; Sebranek and Bacus, 2007).
Although used very little today, nitrate is still included in products, such as dry sausages and dry-cured hams, where an extended maturing process necessitates a long term reservoir of nitrite, the study says.
More recently, nitrate reduction is a common mode of action for indirect curing of “Natural” and “Organic” processed meats made specifically to simulate the typical curing process.
The fixation of a desirable red colour, shaded pink, is the most obvious effect from nitrite addition and is often considered an extremely important attribute for consumer acceptance (Cornforth and Jayasingh, 2004).
Very little nitrite is needed to induce a cured colour. It has been reported that as little as two to 14 parts per million (ppm), depending on species, is necessary to induce a cured colour.
However, significantly higher levels are required to prevent rapid fading and non-uniform curing while also maintaining cured colour throughout an extended shelf life (Sebranek and Bacus, 2007).
When nitrite is added to meat systems, it reacts with or binds to a number of chemical components such as protein (Cassens, 1997b).
Much of the nitrite added during the product manufacturing is either depleted through a series of reactions or physically lost during certain manufacturing steps.
Typically, between 10 and 20 per cent of the originally added nitrite normally remains after the manufacturing process and those levels continue to decline during storage (Pérez-Rodríguez et al., 1996; Cassens, 1997b).
These levels of nitrite, referred to as residual nitrite, slowly decline over the storage life of cured meat products until they are often nondetectable (Skjelkvåle and Tjaberg, 1974; Eakes and Blumer, 1975; Honikel, 2004).
To maintain a cured meat colour throughout extended shelf-life, it is generally accepted that a small amount (10–15 ppm) of residual nitrite is needed to serve as a reservoir for the re-generation of cured meat pigment lost from oxidation and light induced fading (Houser et al., 2005).
The role nitrite has on meat flavour is a complex stimulus involving properties such as aroma/odour, texture, taste, and temperature (Gray et al., 1981).
Nitrite chemistry and the associated reactions likely play a role in imparting the unique flavour resulting from the addition of nitrite; however, the specific compounds involved have eluded scientists and are still not yet known.
Cured meat flavour continues to be one of the least understood aspects of nitrite curing and can be described as ‘at best obscure’ (MacDonald et al., 1980b).
Although clear differences exist between the cured and uncured versions of the same product (e.g., cured ham vs. fresh ham), little is known about what, specifically, is responsible for these differences.
A proposed reason for cured flavour differences between products containing nitrite and those without is due to the nitrite-related suppression of oxidation products; thus controlling rancid flavour compound development (Shahidi, 1998).
However, other commonly used antioxidants do not show this same effect.
One of the most important properties of nitrite is its ability to effectively delay the development of oxidative rancidity.
This prevention occurs even in the presence of salt, which is a strong oxidant.
Lipid oxidation is considered to be a major reason for the deterioration of quality in meat and poultry products, which often results in the development of rancidity and subsequent warmed over flavours (Yun et al., 1987; Vasavada and Cornforth, 2005).
The rate and degree of lipid oxidation is related to the levels of unsaturated fats present as well as temperature, time, oxygen exposure, the removal of oxygen, and the addition of antioxidants and/or reducing agents (Shahidi, 1998).
The antioxidant effect of nitrite is likely due to the same mechanisms responsible for cured colour development involving reactions with heme proteins and metal ions, chelating of free radicals by nitric oxide, and the formation of nitriso- and nitrosyl compounds having antioxidant properties (Sebranek, 2009).
Another important function of nitrite is the role it plays as a bacteriostatic and bacteriocidal agent.
Nitrite has been shown to have varying degrees of effectiveness on either preventing or controlling the growth of certain bacteria.
Studies have shown that nitrite has the ability to control coliform levels in poultry products improving shelf life.
Less nitrite is needed to provide for colour development than to control bacteria (Roberts, 1975). The main portion of nitrite added to cured meats is for C. botulinum control whereas only a small portion (roughly 25 ppm or less) is needed for color development (Sofos et al., 1979a).
However, as nitrite levels increase, control of C. botulinum growth and toxin production also increases (Sofos et al., 1979a).
The complete understanding of the chemistry of nitrite related to cured meat colour and flavour, retarding of fat oxidation, and antimicrobial action still remains elusive.
After decades of research, only a partial understanding of the mechanisms related to the unique nitrite-related properties exist. It is clear that this highly reactive compound, having the capacity to act as an oxidizing, reducing, or nitrosating agent and with the ability of being converted to a number of active compounds including nitric oxide, nitrous acid and nitrate, is an important and yet irreplaceable ingredient.
Concerns Associated with Nitrate and Nitrite
Nitrate and nitrite has been a topic of debate for several decades now.
A critical report in the long-lasting nitrite debate was a 1970 paper by Lijinsky and Epstein (1970) titled “Nitrosamines as Environmental Carcinogens” published in Nature, which showed that nitrosamines were potent and specific carcinogenic compounds.
However, the report says that many epidemiologists, who report associations regarding cured, processed meat and poultry consumption and health risks do not recognise or consider the new findings, knowledge, and understanding surrounding nitrite as a natural metabolite in physiology and its benefits to food safety.
The growing number of studies incorporating epidemiological studies have allowed for more interpretation, and at times extrapolation, by media and consumer groups allowing for growing confusion and inaccurate interpretation of the science.
The relationship between diet and cancer continues to be studied by researchers and headlined in the media.
Several reports have asserted that red meat and/or processed meat consumption have been associated with higher rates of certain types of cancer.
A 2007 report from the World Cancer Research Fund (WCRF), a confederation of cancer research and treatment advocacy groups including the American Institute for Cancer Research (AICR), represented a major global initiative to link diet to cancer (WCRF, 2007).
This WCRF report — Food, Nutrition, Physical Activity and the Prevention of Cancer: a Global Perspective — was released in November 2007.
The report included 10 broad recommendations for cancer prevention regarding diet, lifestyle, and exercise.
Specifically, the report made a recommendation to limit red meat consumption to no more than 18 oz (cooked) per week and eliminate processed meat consumption entirely.
However, curing practices in the meat and poultry industries have been adjusted using the knowledge obtained about nitrosamine risks.
The on-going research focused on the metabolism of nitric oxide, nitrite, and nitrate appears to reaffirm the safety and benefits of current curing practices.
The challenge to meat scientists is two-fold. First, is to continually broaden their understanding of curing in the context of human physiology and metabolism of nitrite and to keep current on the medical literature in this area.
The second is to effectively educate a broad community of public health scientists, nutritionists, and the general public about the fundamental role of nitrite in biology in order to address their unfounded fears and concerns about adverse health effects from consuming cured meat and poultry products.