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Nitrite and Meat Curing

Nitrite and Meat Curing. Cured meats, i.e. ham, bacon, frankfurters etc. are highly distinctive and unique -curing process creates distinctive properties that cannot be duplicated -dramatic quality, shelf life and safety improvement thereby providing highly effective

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Nitrite and Meat Curing

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  1. Nitrite and Meat Curing • Cured meats, i.e. ham, bacon, frankfurters etc. are highly distinctive and unique -curing process creates distinctive properties that cannot be duplicated -dramatic quality, shelf life and safety improvement thereby providing highly effective preservative -duplication of these properties is not straightforward and is difficult to achieve

  2. The net effect of curing involves a very complex series of reactions between curing ingredients and the meat components -many are well understood, many are not • To further complicate matters, some chemical reactions that involve curing ingredients are potentially harmful, while some of the curing agents have more recently been suggested as positive contributors to human health

  3. The Saga of Sodium Nitrite • Nitrite and nitrate have been used for some 5000 years or more to cure and preserve meat, mostly as a salt contaminant (saltpeter=nitrate) • 1891 – first publication showing that nitrate-to-nitrite conversion by bacteria was the source of preservative effects • 1899 – first suggestion of nitrite as the source of cured meat color • 1901 – discovery that nitric oxide from nitrite was source of cured meat color • 1925 – first regulatory (USDA) limits for nitrate and nitrite were established

  4. 1920’s-1950’s – Industry and university researchers refined curing processes - role of nitrite in cured meat clarified -potent antimicrobial agent -powerful antioxidant -distinctive cured meat flavor -unique, attractive color that is stable

  5. 1956 – a problem emerges…; first report of carcinogenic nitrosamines found in fish meal cured with very high nitrite concentrations • 1960’s – intensive studies of the relationship between nitrite, nitrosamines and human cancer… …nitrosamines were found in some cured meats …the perceptions of cured meats as a contributor to human cancer became firmly entrenched

  6. Mid 1970’s – Extensive research in meat curing showed that nitrosamines were not an issue with proper control of nitrite concentrations - use of reductants and improved understanding of time/temperature relationships in meat curing reduced residual nitrite to very low concentrations and eliminated nitrosamines

  7. Late 1970’s – discovery of endogenous nitrate/nitrite in the human intestine and in saliva begins to suggest a biological role for these compounds -leads to discovery of nitric oxide as a very important biological molecule -beginning of the turnaround in scientific perceptions of nitrite

  8. 1986 – Nitric oxide found to be “the body’s messenger” resulting in explosion of research in biology and physiology

  9. Nitric oxide… -regulates blood pressure and blood flow -provides neurotransmission/brain function -kills bacteria and other immune system challengers -promotes healing (also provides critical role in the function of the drug Seldinafil)

  10. 2002 – Importance of nitric oxide for blood transfusions suggested -25% greater heart attacks/strokes observed following transfusions - collected blood loses NO within hours of collection to 30% of initial after one day; 17% after 7 days and virtually none at 42 days - work with dogs showed decreased heart attacks with NO-treated transfusions Reynolds et al., Proc. Nat. Acad. Sci. 104:17058(2007).

  11. 2005 – Protective role of nitric oxide in endothelial function, cardiovascular disease and heart attacks suggested - first reports of nitrite as major storage form of NO in blood and tissue - role for dietary nitrate and nitrite suggested for cardiovascular health

  12. Source of nitric oxide (NO) in biology is nitric oxide synthase (NOS) conversion of arginine to citrulline L-arginine + O2 → L-citrulline + NO + H2O • Nitrite serves as a low-oxygen source of NO thus nitrite may be a critical protective component for increasing blood flow when oxygen is limited • Current questions • role of blood and tissue nitrite concentrations? • role of dietary nitrite?

  13. Dietary nitrite in mice • Insufficiency of dietary nitrite (7 days) decreased steady state nitric oxide and increased injury from heart attacks • Dietary supplementation with nitrite restored NO homeostasis within 7 days, reversed injury and improved survival from heart attacks • Dietary nitrite intake can restore NO homeostasis and blood and tissue nitrite to a greater extent (emphasis mine) than change in NOS activity • Dietary supplementation reduced plaque formation in genetically modified, atherosclerotic-susceptible mice Bryan et al., Proc. Nat. Acad. Sci. 104:19144(2007)

  14. “Most provocatively, these studies suggest that the cardioprotective effects of leafy green vegetables could derive from nitrite, in addition to the often cited antioxidant effects of these food groups.” Gladwin et al. Nat. Chem. Biol. 1:308-314(2005) “The solution to these problems should…lead to the potential consideration of nitrite as an “essential nutrient”…” Gladwin et al. Nat. Chem. Biol. 1:308- 314(2005)

  15. “Could it be that the stringent regulations on nitrite/nitrate in drinking water and in foods contribute to the contemporary diseases of today due to inadequate nitrite or nitrate in the diet and NOS activity unable to supplyenough nitrite to maintain cellular homeostasis?” Bryan, Free Rad. Biol. and Med. 41:691-701(2006) “Therefore, nitrite and nitrate may serve as essential nutrients for optimal cardiovascular health and may provide a treatment modality for cardiovascular disease.” Bryan et al., Proc. Nat. Acad. Sci. Early Ed. (2007). www.pnas.org/cgi/doi/10.1073/pnas.0706579104

  16. Nitrite: • Has profound effects on human physiology • Dietary intake may be protective and maintain/restore endothelial function • Dietary supplementation may inhibit onset and progression of atherosclerosis • Dietary levels of nitrite and nitrate should be reconsidered for optimal health • Increasing steady state NOx concentrations is a natural physiological response in humans and highlights the physiological justification and safety of such intervention fromBryan, MIRC (2007)

  17. Nitrite… • …derives it’s many advantages in cured meats from the unique chemistry of nitric oxide. • …participates in many different chemical reactions during meat curing involving a variety of meat components, but most, if not all, of those reactions produce nitric oxide • …is still not completely understood in some aspects of meat curing and several issues and questions concerning cured meats remain

  18. To understand the issues… …it is necessary to understand and appreciate the complexity of conventionally cured meats

  19. “Cured” meat • Characterized by addition of nitrate and/or nitrite (and salt) • unequivocally defines cured meat (IMHO) • “uncured” otherwise -USDA-FSIS has ruled that any product that has not had nitrate or nitrite added is uncured, however, the USDA recognizes salted (only) products as cured also

  20. Nitrate (NO3-) • Insignificant by itself • Contributes cured meat properties only after reduction to nitrite • Reduction is not easily done by chemical means in meat systems; typically requiring a bacterial culture with nitrate reductase activity • May be important in dried products (hard salami, hams, etc.)

  21. For cured products… “…heated within hours after adding the curing agent, nitrate is useless and superfluous.” Karl Honikel, Federal Research Center for Nutrition and Food, Kulmbach, Germany. (Encyclopedia of Meat Sciences, 2004, p. 196.)

  22. Nitrite (NO2-) • Highly reactive compound • Combines with many different substrates in meat products to provide several highly useful functions = Magic! • Proportional distribution among reactions is likely dependent on product conditions • Understanding nitrite complexity = understanding the issues associated with conventional curing, “natural” curing and the negative consumer image of nitrite and cured meat

  23. Nitrite reactions in meats • Hydrogen ions • Reductants • Meat pigments • Salt • Proteins • Radicals/pro-oxidants • Bacterial cells/cell walls/cell components • Flavor precursors • Lipids

  24. Most obvious effect of nitrite • Color development/change (most often desireable, sometimes not) - addition of nitrite directly affects myoglobin • necessary prerequisite for desirable cured color is nitric oxide (NO) • several reactive intermediates play critical roles for desirable color development by producing nitric oxide

  25. Hydrogen ions 1. Acidic conditions (hydrogen ions) NO2- + H+ → HNO2(nitrous acid) 2HNO2 → N2O3 + H2O (highly reactive intermediate) N2O3 → NO2 + NO (nitrogen dioxide + nitric oxide) (2 NO2 + H2O → HNO3 + HNO2) (Note: nitrate + nitrous acid)

  26. Effects of salt, nitrite and 0.2% GDL on residual nitrite, pH and cured color Treatments Residual nitrite % cured pigment pH Nitrite 75 ppm 20.6b60.3b5.89b 156 ppm 46.7a62.3a5.93a Salt ( with 75 ppm nitrite) 0%35.4a 59.8b5.79e 0.5% 34.9 60.6b5.87d 1.0%35.4a60.8b5.91c 2.0%32.5b61.1b5.96b 4.0%26.0c64.2a6.02a GDL (156 ppm nitrite) 0%40.0a58.7b6.03a 0.2%26.7b63.9a5.79b

  27. 2. Reductants • Natural reductants (NAD, cysteine, cytochromes) • Ascorbate/erythorbate N2O3 + 2 H-Asc ↔ 2 dehydro-Asc + H2O + 2 NO

  28. 3. Myoglobin Mb-Fe+2 + NO2- → MMb-Fe+3 + NO + OH- (purple)(brown) reductant MMb-Fe+3 + NO →MMb-Fe+3–NO →Mb-Fe+2–NO (brown)(brown)(red)

  29. Nitrite concentration effects on raw meat color 0 ppm 0.5 ppm 1.0 ppm 2.5 ppm 5.0 ppm 10.0 ppm 15.0 ppm 20.0 ppm 25.0 ppm 50.0 ppm Sebranek and Turner, 2002. Meat Process. 41(9):52-55.

  30. Salt (NaCl) HNO2 + H+ + Cl- ↔ NOCl + H2O (highly reactive) NOCl + Mb-Fe+2 → Mb-Fe+2– NO + Cl- (purple)(red)

  31. NaCl and ascorbate effects on measurable nitrite in cooked meat Salt (mM) Ascorbate Nitrite (% of initial) Fox et al.,1981.J. Assoc. Off. Analyt. Chem. 64:1397-1402.

  32. Proteins/sulfhydryl groups R-SH + 2 HNO2 → R-S-S-R + 2 H2O + 2 NO sulfhydryl disulfide -besides generating nitric oxide, this reaction has been suggested as a contributor to increased firmness on cured meat by crosslinking proteins with the disulfide bond

  33. In addition to cured color development from the various sources of nitric oxide • Nitrite is strongly inhibitory of anaerobic bacteria, particularly Clostridium botulinum • dependent on pH, salt, reductants, iron content • Interestingly, these are many of the same factors that favor nitrous acid and nitric oxide production

  34. Is ingoing or residual nitrite most important to bacterial control? • USDA requires minimum of 120 ppm ingoing for cured products that are refrigerated • Research suggests that residual nitrite is critical to antibotulinal effects • Most commercial cured meats at retail have less than 15 ppm residual nitrite Probably…a certain minimum ingoing amount is necessary to achieve initial inhibition, given competitive chemical reactions, and a certain residual amount is necessary for sustained inhibition but the the amounts of each are unclear and probably dependent on several other inherent conditions in the product

  35. Nitrite provides potent antioxidant effectiveness • Stabilizes heme iron • Chelates metal ions and radicals • Reacts with unsaturated lipids

  36. Fish, chicken, pork and beef -measured 48 hours post-cook Morrissey and Tichivangana, 1985. Meat Sci. 14: 175-190.

  37. Role in cured flavor? • Over 100 volatiles identified in cured ham • Not well understood -part of antioxidant effect? -more reaction products of nitrite/nitric oxide?

  38. Nitrite safety issues • Toxicity -highly toxic (~70 mg/kg body weight, i.e. 4-5 gram dose) -inconsequential in normal cured meat applications because of extremely low concentration • Nitrosamines issue -secondary amines (-NH) may react with nitrite (or nitrous acid (nitrosating intermediates) to form -N-NO (nitrosamine) -most are definite carcinogens, some are quite potent - epidemiological studies based on nitrosamine hypothesis • “Natural” curing -significantly reduced nitrite concentration, indistinguishable appearance

  39. There are a number of processed meat products, mostly natural and organic cured meats, being introduced in the market that are labeled “Uncured” and “No nitrites or nitrates added”.

  40. Ingredients: Organic grass-fed beef, water, sea salt, organic spices, organic garlic powder, organic paprika, celery powder, organic onion, lactic acid starter culture

  41. Even though labeled “uncured”, almost all of these products display all the typical cured meat properties that are derived from addition of sodium nitrite, and that can be achieved ONLY with sodium nitrite… Further, chemical analyses of the products confirm the presence of nitrite and nitrate. Thus…the oxymoron in labeling; uncured = cured

  42. Why the oxymoron…? …why is “Uncured” and “No nitrites or nitrates added” used on the label of products that are unequivocally cured in terms of both product properties and the presence of curing agents?

  43. USDA has required that uncured versions of “typical” cured meats be “… labeled with such standard name when immediately preceded with the term “Uncured” in the same size and style of lettering as the rest of such standard name…” Code of Federal regulations 9 CFR 319.2 (2006)

  44. “Natural” (processed meats) definition: • “…does not contain any artificial flavor or flavoring, coloring ingredient, or chemical preservative…”(USDA Food Standards and Labeling Policy Book, 2005)

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