See, Bacon & the Art of Living, Chapter 11.01: The Fathers of Meat Curing
These are the men who laid the scientific foundation that resulted in the change from the use of saltpeter to sodium nitrite in meat cures. Initially, the reactions of nitrite and nitric oxide () were studied separately until Haldane showed that nitrite only had value as the initiator of a reaction sequence that produce nitric oxide ().
Note that hemoglobin is used in the early studies. The reason is “mostly a matter of convenience” and “a matter of necessity since myoglobin was not isolated and purified until 1932 (Theorell, 1932).” “In spite of the differences between hemoglobin and myoglobin, Urbain and Jensen (1940) considered the properties of hemoglobin and its derivatives sufficiently like those of myoglobin to allow the use of hemoglobin in studies of meat pigments.” (Cole, Morton Sylvan, 1961: 2)
These are the pioneers of our current understanding of the chemistry of curing.
Humphrey Davy (1778 – 1829) in 1812 (cited by Hermann, 1865) and Hoppe-Seyler (1864) was the first to note the action of nitric oxid upon hemoglobin. (Hoagland, R.; 1914: 213)
Hermann (1865) studied the properties of the compound formed in the reaction between hemoglobin and nitric oxide.
He showed the spectrum of oxyhemoglobin and NO-hemoglobin. “The blood saturated with nitric oxid was found to be darker in color than either arterial blood or that saturated with carbon monoxid.” (Hoagland, R.; 1914: 213)
On 7 May 1868, Dr. Arthur Gamgee from the University of Edinburgh, brother of the famous veterinarian, Professor John Gamgee (who contributed to the attempt to find ways to preserve whole carcasses during a voyage between Australia and Britain), published a groundbreaking article entitled, “On the action of nitrites on the blood.” He observed the colour change brought about by nitrite. He wrote, “The addition of … nitrites to blood … causes the red colour to return…” Over the next 30 years, it would be discovered that it is indeed nitrites responsible for curing and not the nitrates added as saltpeter.
It fell upon a German researcher, Dr. Ed Polenske (1849-1911), working for the Imperial Health Office in Germany, to make the first discovery that would lead to a full understanding of the curing action. He prepared a brine to cure meat and used only salt and saltpeter (nitrates). When he tested it a week later, it tested positive for nitrites.
The question is where did the nitrites come from if he did not add it to the brine to begin with. He correctly speculated that this was due to nitrate being converted by microbial action into nitrite. He published in 1891.
Following Dr. Polenski’s observation, the German scientist, Nothwang confirmed the presence of nitrite in curing brines in 1892 but attributed the reduction from nitrate to nitrite to the meat tissue itself. The link between nitrite and cured meat colour was finally established in 1899 by another German scientist, K. B. Lehmann in a simple but important experiment.
Karl Bernhard Lehmann (1858 – 1940) was a German hygienist and bacteriologist born in Zurich.
In an experiment he boiled fresh meat with nitrite and a little bit of acid. A red colour resulted, similar to the red of cured meat. He repeated the experiment with nitrates and no such reddening occurred, thus establishing the link between nitrite and the formation of a stable red meat colour in meat.
K. B. Lehmann made another important observation that must be noted when he found the colour to be soluble in alcohol and ether and to give a spectrum showing an absorption band just at the right of the D line, and a second band, often poorly defined, at the left of the E line. On standing, the color of the solution changed to brown and gave the spectrum of alkaline hematin, the colouring group.
In the same year, another German hygienists, one of Lehmann’s assistants at the Institute of Hygiene in Würzburg, Karl Kißkalt (1875 – 1962), confirmed Lehmann’s observations and showed that the same red colour resulted if the meat was left in saltpeter (potassium nitrate) for several days before it was cooked.
The brilliant British physiologist and philosopher, John Scott Haldane weighed in on the topic. He was born in 1860 in Edinburgh, Scotland. He was part of a lineage of important and influential scientists.
J. S. Haldene contributed immensely to the application of science across many fields of life. This formidable scientist was for example responsible for developing decompression tables for deep sea diving used to this day.
“Haldane was an observer and an experimentalist, who always pointed out that careful observation and experiments had to be the basis of any theoretical analysis. “Why think when you can experiment” and “Exhaust experiments and then think.” (Lang, M. A. and Brubakk, A. O. 2009. The Haldane Effect)
S. J. Haldele applied the same rigor to cured meat and became the first person to demonstrate that the addition of nitrite to hemoglobin produce a nitric oxide (NO)-heme bond, called iron-nitrosyl-hemoglobin (HbFeIINO).
Haldane showed that nitrite is further reduced to nitric oxide (NO) in the presence of muscle myoglobin and forms iron-nitrosyl-myoglobin. It is nitrosylated myoglobin that gives cured meat, including bacon and hot dogs, their distinctive red color and protects the meat from oxidation and spoiling.
This is how he discovered it. Remember the observation made by K. B. Lehmann that the colour of fresh meat cooked in water with nitrites and free acid to give a spectrum showing an absorption band just at the right of the D line, and a second band, often poorly defined, at the left of the E line.
Haldane found the same colour to be present in cured meat. That it is soluble in water and giving a spectrum characteristic of NO-hemoglobin. The formation of the red color in uncooked salted meats is explained by the action of nitrites in the presence of a reducing agent and in the absence of oxygen upon hemoglobin, the normal coloring matter of fresh meats. He showed that the redox reaction occurs in meat during curing (1901).
Haldane finally showed the formation of nitrosylhemochromogen from nitrosylhemoglobin (nitrite added to hemoglobin) when thermal processing has been applied and identified this as the pigment responsible for the cooked cured meat colour. He attributed this formation to NO-hemoglobin denaturing into two parts namely hemin (the colouring group) and the denatured protein (1901).
Ralph Hoagland, Senior Biochemist, Biochemie Division, Bureau of Animal Industry, United States Department of Agriculture, published an article in 1914, Coloring matter of raw and cooked salted meats. In this article, he shows that nitrite as curing agent was a known and in theory an accepted fact by the outbreak of World War One.
Ralp Hoagland (1908) studied the action of saltpeter upon the colour of meat and found that its value as an agent in the curing of meats depends upon the nitrate’s reduction to nitrites and the nitrites to nitric oxid, with the consequent production of NO-hemoglobin. The red colour of salted meats is due to this compound and that the nitrite anion is not the reactant. He showed that the reactant is nitrous acid () or one of its metabolites such as nitric oxide ().
Hoagland conclusively shows that saltpeter, as such, has no value to preserve the fresh colour.
Concerning the direct addition of nitrite to curing brine
Additional information references:
Cole, Morton Sylvan, “Relation of sulfhydryl groups to the fading of cured meat ” (1961). Retrospective Theses and Dissertations. Paper 2402
Hoagland, R. 1914. Cloring matter of raw and cooked salted meats. Laboratory Inspector, Biochemie Division, Bureau of Animal Industry. Journal of Agricultural Research, Vol. Ill, No. 3 Dept. of Agriculture, Washington, D. C. Dec. 15, 1914.
J S Haldane: https://en.wikipedia.org
An Earthworm Express publication.