Sodium nitrate (NaNO3) is a food preservative used for meat. Nitrates are used in curing, which is a broad category of techniques for preserving foods, mainly meat and fish, that involves the use of salt, sugar, or some form of dehydration. In each case, the goal is to make the food unattractive to the bacteria that cause food spoilage. This works because bacteria are tiny organisms that require, among other things, moisture, oxygen and food. Take away one of these things and they die. One special property of sodium nitrite is that it prevents the growth of Clostridium botulinum.
One of the most toxic substances known, Clostridium botulinum produces botulism, a paralytic illness that can lead to respiratory failure.
The botulism bacteria is peculiar bug because unlike most microbes, it actually requires an oxygen-free environment to live. Once it hits the air, it dies. So it tends to appear in canned foods, vacuum-packed foods, garlic stored in oil and improperly cured meats. It just so happens that sodium nitrate is especially effective at preventing the growth of Clostridium botulinum. Sodium nitrate also conserves the organoleptic qualities of the meat and helps to keep the tipical red brilliant colour of fresh meat.
Sodium nitrate is used in Dutch cheese as well as many meats, such as, cured meats, bacon, ham, tongue, sausages, wurstel, smoked frankfurters, pressed or tinned meats, but also in fish e poultry.
However sodium nitrate can be dangerous for human health because it causes methaemoglobinaemia and because it is linked with cancerogenic effects.
Sodium nitrate (NaNO3) has no negative effects on our organism but when we eat sodium nitrate a part of it, approximately 5%, is transformed in sodium nitrite (NaNO2) by the bacterial flora in the oral cavity. Sodium nitrite is the real dangerous molecule that causes methaemoglobinaemia and has carcinogenic effects.
Methaemoglobinaemia
Methaemoglobinemia is a disorder characterized by the presence of a higher than normal level of methemoglobin in the blood. Methemoglobin is an oxidized form of hemoglobin that has a decreased affinity for oxygen, resulting in an increased affinity of oxygen to other heme sites and overall reduced ability to release oxygen to tissues. The hemoglobin has Fe2+ ion while the methemoglobin has Fe3+ ion. The oxygen–hemoglobin dissociation curve is therefore shifted to the left. Spontaneous formation of methemoglobin is normally reduced (via electron donation) by protective enzyme systems, like NADH methemoglobin reductase (cytochrome-b5 reductase), NADPH methemoglobin reductase and to a lesser extent the ascorbic acid and glutathione enzyme systems. When methemoglobin concentration is elevated in red blood cells, tissue hypoxia can occur. Normally methemoglobin levels are less than 1% but if this rate raises, the symptoms can include shortness of breath, cyanosis, mental status changes, headache, fatigue, exercise intolerance, dizziness and loss of consciousness.
The iassumption of a large quantity of sodium nitrate leads to methaemoglobinaemia. Many cases of this kind of desease are reported as a consequence of ingestion of meat with an high sodium nitrate and nitrite content.
Sodium nitrite gives the typical red colour to meat, cold cuts and sausages because of the oxidation of myoglobin in them. In the same way sodium nitrite causes oxidation of hemoglobin in blood cells causing methaemoglobinaemia.
Links
Faulty sausage production causing
methaemoglobinaemia. 1997
Nitrite-induced methaemoglobinaemia. 1987
Methemoglobinemia from eating meat with high nitrite content. 1957
Carcinogenic effects
Sodium nitrite has cancerogenic effects because it causes the formation of nitrosamines that are cancerogenic molecules. Such carcinogenic nitrosamines can be formed from the reaction of nitrite with secondary amines under acidic conditions (such as occurs in the human stomach) as well as during thecuring process used to preserve meats.
Sodium nitrite (NaNO2) in human stomach becomes nitrous acid (HNO2) because pH in the stomach is very low. This reaction happens especially in children, because stomach pH is lower than adults. This is because sodium nitrite is very dangerous for children.
Nitrous acid then can react with amines forming nitrosamines. The cancerogenic effect of nitrosamines has been proven by many studies. The biochimical reaction that causes cancer is the alkilation of DNA bases. Alkylation is the transfer of an alkyl group from one molecule to another. The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion or a carbine. Alkylating agents are widely used in cell reactions in order to repair DNA but an excess lead to an uncontrolled and unintended reaction that damages DNA. Alkylation with only one carbon is termed methylation.
Clinical studies confirmed the relationship between dietary intake of nitrates and stomach cancer risk, but it is also connected with all gastrointestinal tract.
Links
Dietary intake of polyphenols, nitrate and nitrite and gastric cancer risk in Mexico City. 2009
Processed meat consumption, dietary nitrosamines and stomach cancer risk in a cohort of Swedish women. 2006
Nitrosamines, alcohol, and gastrointestinal tract cancer: recent epidemiology and experimentation. 1996
Conclusion
Nitrates and nitrites certainly not healty. To limit the intake of these molecules we can reduce the assumption of cold cuts and sausages, we can read the ingredient list of the products we buy and we can pay attention to the colour of the meat we buy, a red brillant colour can be a sign of the presence of sodium nitrate or other preservatives.
