Curing nitrite

In meat curing, nitrite is traditionally used for developing the pink, heat-stable pigment. Its other important role is the inhibition of the outgrowth of Clostridium botulinum spores in pasteurized products and, in some countries, in several types of smoked fish. Nitrite also serves as an antioxidant and contributes positively to the development of the flavor of cured-meat. The undesirable side-effect, however, is the reaction of nitrite with amino groups of food constituents, leading to the formation of NNCs. 

N Nitrosopyrrolidine (formed when bacon that has been cured with sodium nitrite IS fned)... 

Sodium Nitrate and Sodium Nitrite. Nitrates and nitrites ate used in meat-curing processes to prevent the growth of bacteria that cause botulism. Nitrates have been shown to form low, but possibly toxic, levels of nitrosamines in certain cured meats. For this reason, the safety of these products has been questioned, and use is limited (80). 

Nitrates are found in fairly high concentrations in beets, spinach, kale, coUards, eggplant, celery, and lettuce. AdditionaHy, nitrates and nitrites are commonly used in the curing solutions of bacon, ham, and other cured meats. In cured meats, nitrates and nitrites control the growth of microorganisms, particularly Clostridium botulinum, and also serve as color preservatives. 

Nitrite is part of the preserving process for cured meats. Cigarette smoke contains high levels of nitrite. 

Sodium nitrite can react with proteins in the stomach or during cooking, especially in high heat (such as frying bacon), to form carcinogenic N-nitrosamines. To prevent this, ascorbic acid or erythor-bic acid is commonly added to cured meats. 

During the curing process, some of the nitrites are converted to nitric oxide. This combines with the myoglobin proteins in the muscle of the meat to form the deep red nitric oxide myoglobin, which causes cured meats such as ham to turn pink during the smoking process. 

Sodium nitrate has been used for centuries to cure meat. Bacterial action during curing converts the sodium nitrate into sodium nitrite, which kills the bacteria that cause botulism, and combines with the myoglobin in the meat to form the pink color associated with ham. 

These days, sodium nitrite replaces most of the sodium nitrate used in cured meats, except for that used in slow-cured country ham. 

Most nitrites are soluble in water and mildly toxic. Despite their toxicity, nitrites are used in the processing of meat products because they retard bacterial growth and form a pink complex with hemoglobin that inhibits the oxidation of blood (a reaction that would otherwise turn the meat brown). Nitrites are responsible for the pink color of ham, sausages, and other cured meat. 

PEGG R B, FISH K M and SHAHIDI F (2000) The replacement of conventional meat curing with nitrite-free curing system, Fleischwirtschaft, 80 (5) 86-9. 

THiEMiG F, BUHR H, OELKER p (2000) Curing with nitrite - are there alternatives , Fleischwirtschaft, 80 (1) 106-10. 

N-Nitrosamines, formed principally from the reaction of naturally occurring secondary amines with nitrites that may be added to foods or produced by bacterial reduction of nitrates, have been identified in many food systems including cured meat products, nonfat dried milk, dried malt and beer. In addition, the presence of less volatile and non-volatile N-nitroso compounds or their precursors in foods have been suggested from a number of model system studies. 

N-Nitrosamines in Cured Meats Other Than Bacon. The presence of N-nitrosamines in cured meats other than bacon has been the subject of several recent surveys (19,58,59). In general, the majority of the positive samples contained extremely low levels of N-nitrosamine, usually less than I yg/kg (19,58). This low level could, in part, be attributed to the discontinuation of the use of nitrite-spice premixes in the mid-l970 s (l 9). In the Holland study (59), the predominant N-nitrosamines detected were NDMA and N-nitrosomorpholine (NMOR) and, generally, values of 4 yg/kg were obtained for each N-nitrosamine. More correctly, these are presumptive N-nitrsoamine levels since mass spectral confirmation of their identities was not achieved. 

In other working areas the reduction of airborne nitrosamines is possible, too. In a special curing process using a nitrite-nitrate salt bath for tube... 

In the last fifteen years there has been considerable interest in the analysis of volatile N-nitrosamines in foods. The primary focus has been on meat cured with nitrite (3 ) although nitrosamines have been shown to occur occasionally in other foods such as fish and cheese (, 3) Recently, attention has been directed to volatile nitrosamines in beer and other alcoholic beverages. The purpose of this paper is to review current information on the presence of nitrosamines in beer, and to discuss work done in our laboratory and elsewhere on the mode of formation of nitrosamines in beer. 

The functions of nitrite added to meat for the purpose of curing are now well known by many people because of the extensive publicity given to the process via the popular press. Nitrite added to meat results in a typical color and a characteristic flavor, provides microbiological protection especially against outgrowth of C. botulinum spores and may play a role in textural characteristics. 

There has been a long standing discussion whether nitrite produces a cured flavor or retards development of an off-flavor. 

A review by Bailey and Swain ( ) cited several references which indicated nitrite was responsible for cured meat flavor. These same authors presented chromatograms of volatiles from cured and uncured hams and while the chromatograms were similar, some quantitative differences led to the conclusion that the major difference due to nitrite was its reactivity to retard lipid oxidation. Greene and Price ( ) suggested, however, that sodium chloride was the major factor responsible for cured meat flavor rather than sodium nitrite or an absence of lipid oxidation. It has been concluded from other recent work (2) that nitrite was necessary to produce a typical ham aroma and flavor as well as to retard the development of off-odors and flavors during storage of cooked cured meat. 

Nitrite is an extremely reactive chemical and is soluble in the aqueous phase of meat. It is usually used for curing in the form of the sodium salt. The nitrite ion is the conjugate base of nitrous acid (a weak acid) and has a PK of 3.36. The usually mild acid conditions found in meat give formation of only a small quantity of nitrous acid when nitrite is added to the meat ( ) ... 

Cytochrome c is a heme containing protein which occurs in muscle at lower concentrations than does myoglobin. It was demonstrated some time ago (18) that oxidized cytochrome c reacts with gaseous nitrite oxide to produce a nltrosyl compound. Recent work (19, 20, 21) has examined the reactions of cytochrome c with nitrite and the contribution of the product formed to cured meat color in considerably more detail. The general conclusion is that even at the pH normally encountered in meat, the reaction can take place in the presence of ascorbic acid but probably does not affect meat color because of the unstable nature of the reaction product and the low concentration. 

In fact, as will be indicated later in this manuscript, the proteins of meat are the major constituent with which nitrite reacts and explain the largest proportion of the nitrite lost from analytical detection during curing. While considerable discussion has occurred about this so called protein bound nitrite, little has been substantiated about identification and quantitation of the reaction products. Protein bound nitrite has been of concern in analysis for free nitrite because depending on conditions of analysis, some portion of it may be released and measured. 

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