Monday, 13 February 2012

Nitrates, Nitrites, Meat and Meat Products

Nitrates, Nitrites, Meat and Meat Products

Nitrates and Nitrites are fundamental components of the global nitrogen cycle and are therefore found throughout the environment. Nitrates and nitrites are compounds that contain a nitrogen atom joined to oxygen atoms, with nitrate containing three oxygen atoms and nitrite containing two. In nature, nitrates are readily converted to nitrites and vice versa. Both are anions or ions with a negative charge. They tend to associate with cations, or ions with a positive charge to achieve a neutral charge balance. (Argonne National Laboratory, 2005).

Chemical Symbol
Molecular weight

Table 1: Chemical symbols of nitrate, nitrite and their molecular weights.

The role of Nitrates and Nitrites in Cured Meat Products

Potassium and sodium salts of the nitrate and nitrites are the most extensively used of all food additives (Stevanovic and Šentjurc, 2000). Nitrates and nitrites in cured meat and meat products play a multipurpose role; in addition to effectively inhibiting the growth and toxicogenic effect of Clostridium botulinum, nitrite is responsible for the development of typical cured-meat color and flavor, and also functions as an antioxidant (Rincón et al., 2008), retarding the development of rancidity, off-odors and off-flavors during storage, inhibiting the development of warmed-over flavor and preserving flavors of spices and smoke (Zdzlaslaw, 2002).
Adding nitrite to meat is only part of the curing process (Feiner, 2006). Ordinary table salt (sodium chloride) is added because of its effect on flavor. Sugar is added because of its contributions to flavor, browning during frying process and its ability to disguise high levels of salt in a meat product. Spices and other flavorings are often added to contribute to flavor, aroma and taste but not added for nutritional purposes (Feiner, 2006).
Sodium nitrite, rather than sodium nitrate, is the most commonly used for curing (although in some products, such as country ham, sodium nitrate is used because of the long aging period) (Stevanovic and Sentjuric, 2000). In a series of normal reactions, nitrite is converted to nitric oxide (Fennema, 1996). Nitric oxide combines with myoglobin, the pigment responsible for the natural red color of uncured meat forming nitric oxide myoglobin, which is a deep red color (as in uncooked dry sausage). This changes to the characteristic bright pink normally associated with cured and smoked meat (such as wieners and ham) when heated during the smoking process (Feiner, 2006).
When sodium nitrite is added with the salt, the meat develops a red, then pink color, which is associated with cured meats such as ham, bacon, hot dogs, and bologna. Nitrite reacts with the meat myoglobin to cause these color changes, first converting to the unstable nitrosomyoglobin (bright red), then on heating, to a more stable nitrosohemochrome, a pink pigment (Zdzlaslaw, 2002; Fennema, 1996).

Fig 5; Transformation of myoglobin in meat; dMMb and dMbNO, denatured forms of pigments (Zdzlaslaw, 2002)
Modification of the myoglobin molecule takes place in the meat curing process where nitric oxide (NO), which originates from the sodium nitrite or potassium nitrite curing agent, combines to form nitrosomyoglobin (Fennema, 1996).
According to Feiner (2006), this reaction takes place at pH value below 6.5 and in meat products a pH value of a round 4.7(salami) to 6.0 is present in the final product. When used, sodium nitrate (NaNO3) does not contribute directly to the formation of the red curing color but rather reduced to sodium nitrite (NaNO2) thus providing nitric oxide (NO) by the reactions above, which results into the formation of the characteristic pink cured meat color (Feiner 2006, Fidel, et al, 2009). Examples such products are; ham, corned beef, bacon, salami, and sausage.

Fig 6; Chemical structures of myoglobin and nitrosomyoglobin (http://nzic.org.nz/ChemProcesses/animal/5A.)

In the presence of thiol compounds as reducing agents in the reversible reaction, myoglobin may form a green sulfmyoglobin (Zdzlaslaw, 2002). Other reducing agents, for example ascorbate lead to formation of cholemyoglobin making the reaction irreversible (Fiener, 2006).
Animal blood and its dehydrated protein extracts, which are mainly hemoglobin, are a potential source of red and brown heme pigment which may be used as red and brown coloring to meat products. However in most countries their usage as food colorant is not permitted (Zdzlaslaw, 2002).

Meat, nitrates, nitrites and cancer
Colorectal cancer is the main cancer type that has been associated with high meat consumption. Based on a considerable number of studies a 12–17% increased risk of colorectal cancer was associated with a daily increase of 100 g of red meat and a 49% increased risk associated with a daily increase of 25 g of processed meat (ferguson, 2010). Processed meats include sausages, smoked beef and hams among others in which case nitrates and nitrites are used as additives.

Hill (1991) reported that the use of nitrites in cured meats experienced a serious drawback in the late 1960s in the usa due to the n-nitrosamines scare. The presence of some n-nitrosamines, as a consequence of the reaction of nitrites with secondary amines especially in thermally treated cured meats, caused a ban in the usa that was lifted after re-considering maximum amounts to be added. A number of n-nitrosamines are potential carcinogenic agents and are postulated to have several deleterious health effects, so their formation must be prevented. According to stevanivic and senjurc (2002) and hill (1991), the addition of ascorbic acid ensured the reaction of nitrite to nitric oxide and thus reduced the possibility for the formation of n-nitroso compounds in meat products. N-nitroso compounds are formed by the action of nitrous acid on a suitable secondary nitrogen group. If the parent nitrogen group is a secondary amine, then the product is an n-nitrosamine giving rise to n-nitrosamides, ureas to n-nitrosoureas, all of which are carcinogenic to the body. The n-nitrosamines are target organ specific and cause tumors at sites distant from that of their introduction into the body. N-nitrosamide and n-nitrosoureas are locally acting and cause tumors only at their sites of introduction. The n-nitrosamines are not directly acting mutagens but need activation by microsomal enzymes before they are mutagenic in the salmonella mutagenesis assay. They also need to be activated in the body, but this process which leads to the organotropism of these compounds, is little understood (hill 1991)

In reference to the above, it is therefore necessary to develop alternatives to nitrates and nitrites. Researchers have proposed different methods to inhibit the possibility of N-nitrosamine formation in cured meat products. These include a decrease in the level of added nitrite or the use of N-nitrosamine blocking agent such as ascorbate and α- tocopherol (Stevanivic and Senjurc, 2002). However, as far as N-nitrosamines are concerned, the most attractive and reliable method is total elimination of nitrites and nitrates from the curing process. The alternative of natural plant colorants extracted directly from plants or plant parts that totally eliminate the use of nitrite from the curing process can be a viable alternative for coloring comminuted meat as a substitute for nitrates, nitrites and synthetic colorants to give the products their characteristic pink color.

Note that all references used in all postings related to the topic of sausages, meat and meat product colorings will be posted in the last article about this topic.
About the author
Mr. Sempiri Geoffery, the author of this article
graduated from Makerere University with a Bsc In Food Science and Technology Degree in January, 2011.