Erythorbate

Erythorbate
Eben van Tonder
9 February 2018

Proper bacon.jpg
Proper Bacon, produced and photographed by Robert Goodrick.  An example of a good cut and excellent curing.  His technique with this batch of bacon was dry curing, 4 days before a quick rinse and hung to equalize for close to two weeks.  No vacuum bags, meat lugs and open.  Temperature is 2 C.

INTRODUCTION

In meat curing, sodium erythorbate [E316] (C6H7NaO6) functions as an antioxidant, to increase the rate of nitrite reduction to nitric oxide which reduces the amount of residual nitrite in cured meat after curing sufficiently took place.  In the modern curing plant, speeding up the formation of nitric oxide from nitrite is important because it speeds up the curing time, but far more important than this, it reduces the nitrite levels left in the meat after curing.  Nitrite itself, at the minuscule levels used in meat curing, is not dangerous to human health, but “unreacted” nitrite forms n-nitrosamines during frying and in the stomick which have been linked to the development of various cancers.  The meat industry responded to this by including either ascorbate (Vitamin C) or erythorbate in curing mixes as anti-oxidants.  Including either ascorbate or erythorbate in bacon is one of the ways that bacon is changed into a safe food. (1)   (see Regulations of Nitrate and Nitrite post-1920:  the problem of residual nitrite)

Ascorbic acid and erythorbate have been widely used in recent years to improve the color of cured meats. Watts and Lehman (1952a) found that 0.1 percent ascorbic acid added to meats caused better color development when the meat was heated at 70°C. or frozen at -17°C. These workers (1952b) observed that hemoglobin did not react with ascorbic acid in the absence of oxygen. Ascorbic acid reduced methemoglobin and promoted the reduction of nitrite to nitric oxide. In the presence of oxygen, an undesirable side reaction occurred in which the green pigment choleglobin was formed. According to Hollerbeck and Monahan (1953), the beneficial effect of ascorbic acid in curing meat is due to the reduction of nitrogen dioxide to nitric oxide. Kelley and Watts (1957) observed that cysteine, ascorbic acid, and glutathione were capable of promoting the formation of nitric oxide hemoglobin, regenerating this pigment on surfaces of faded meat and protecting surfaces of cured meat from fading when exposed to light.” (Cole, 1961) (Reaction Sequence)

Erythorbate is many times more expensive than ascorbate, making this a favourite for inclusion in curing brines and accounts for its widespread use.  Chemically, erythorbic acid’s sodium salt is sodium erythorbate.  We will use erythorbate in this article to refer to either one of the two forms.

Erythorbic acid is a stereoisomer of ascorbic acid (vitamin C), meaning that the two compounds differ only in the spatial arrangement of their atoms.  Previously it was called isoascorbic acid, D-araboascorbic acid.  (Walker, R)

I wondered where and how this compound was discovered and if it occurs naturally.

ANTI-SCORBUTICS

The isolation and identification of vitamin C or ascorbic acid at the beginning of the 1930’s was a big deal.  It solved the riddle of the anti-scurvy agent which eluded humans for centuries (see Concerning the Discovery of Ascorbate)  and after its identification, science moved to learn everything there was about it.  The most urgent question now became its synthesis which would allow it to be produced in massive quantities, in the cheapest possible way, offering untold wealth for those who would achieve this.

The priority was justified.  Scurvy was a widespread, universal problem, not just for the navy.  Notes by Tamango Ltd., On the prevention of scurvy among native workers; Oranges and  Orange Juice,  published in May 1936 deals with the prevalence of scurvy among the native population and its impact on industries like gold and diamond mining in the Free State, Gauteng and Northern Cape and the sugarcane industry in Natal.  It even deals with scurvy and it’s widespread occurrence among native school children.  It offered as a solution to vitamin C deficiency which, according to the authors, hampered the growth of the economy of the Union of South Africa, the mass production of citrus fruit and instead of exporting it all, to make this available for industry to feed its workforce.

Apart from being highly informative on another subject of great interest to me namely the traditional diets of native populations across the world and the negative impact of colonization on these societies, it highlights the priority that vitamin C had in our world in the late 1800’s and early 1900’s in the context of finding the best and cheapest available source, especially after its isolation and identification in the early 1930’s. (2)

ARABO-ASCORBIC ACID OR ERYTHORBIC ACID

In 1933 and 1934, researchers showed that synthesised d and l-ascorbic acid and prepared synthetic analogues.  One of these they called arabo-ascorbic acid (from arabinosone).    The product was synthetically derived from an osone (an osone is a compound that contains two alpha carbonyl groups and is obtained by hydrolyzing an osone).  (Ault, 1933 and Baird, 1934)  The reason for their work has been a well-established method by this time in the development of new pharmaceutical medicines.  According to this method, an initial compound is identified (referred to as the lead compound).  This compound possesses the activity of interest.  Such an activity of interest may exist in the particular compound along with some undesirable characteristics such as toxicity, unsuitable half-life or poor availability (in vivo).  A process is then embarked on to develop and analyze analogs of such a lead compound and to evaluate their different characteristics.  (Gutte, B.. (Ed); 1995: 396)

It seems that it was the German chemists, Kurt Maurer and Bruno Schiedt who, in August 1933,  were the first researchers to have synthesized erythorbic acid.  (Maurer and Schiedt, 1933)  It is estimated to be only one-twentieth as effective as ascorbic acid (Daniel and Munsell; 1937:  6) and is not capable of preventing scurvy but it nevertheless possesses great oxygen reducing characteristics which makes it ideal for industrial application due to its ease of production.

The researchers Takahashi, T.,  et al. became the first to report on the production of  D-araboascorbic acid from penicillin.  This was important since it showed that erythorbate was indeed a naturally occurring product.  They refer to Isherwood, et al. who also found it in cress seedling in D-altrono-r-lactone solution and in the urine of rats injected with D-mannono-r-lactone.

A strain of Penicillium which they isolated from soil produced D-araboascorbic acid (erythorbic acid) from D-glucose, D-gluconic acid and sucrose.  (Takahashi, T.,  et al.  1960)

Today it is synthesized by a reaction between methyl 2-keto-D-gluconate and sodium methoxide. The method of synthesizing it from sucrose or by strains of Penicillium are still in use.

The exact meaning of the prefix “erythor” eludes me and there is no connection with the similar sounding prefix, “eryhro” meaning red which would be a tidy connection with meat curing, but several sources refute this.

Dr R. Walker, Professor of Food Science, Department of Biochemistry, University of Surrey, England, offers the following information:  “Erythorbic acid (syn: isoascorbic acid, D-araboascorbic acid) is a stereoisomer of ascorbic acid and has similar technological applications as a water-soluble antioxidant. This compound was previously evaluated under the name isoascorbic acid; at the last evaluation an ADI of 0-5 mg/kg b.w. was allocated, based on a long-term study in rats, and a toxicological monograph was prepared. The name was changed to erythorbic acid in accordance with the “Guidelines for designating titles for specifications monographs.” (Dr. R. Walker)

CONCLUSION

This is only a brief introduction.  In my experience, there is little difference in curing time between the use of erythorbate or ascorbate and the price difference is material.  I have noticed that some producers include a mixture of both compounds in their brine preparations.  I would love to know the exact reason why this is done and to have a look at the data.  Another aspect of great interest is its characteristic as a potent enhancer of nonheme-iron absorption.  This is, however, again, outside the realm of meat curing and will have to happen in a different format.

Notes:

  1.  The other ways in which this has been accomplished over the years are to restrict the amount of nitrite allowed in curing and to prevent the simultaneous use of nitrite and nitrate in meat such as bacon with are produced using relatively short curing times.  (see Regulations of Nitrate and Nitrite post-1920:  the problem of residual nitrite)
  2. The document from Wits mentions Pryde (1931) who quotes Herbert Spencer’s “ Study of Sociology (1880) ” concerning the early use of Citrus juices for the cure of scurvy:— “ It was in 1593 that sour juices were first recommended by Albertus, and in the same year Sir R. Hawkins cured his crew of scurvy by lemon-juice. In 1600, Commodore Lancaster, who took out the first squadron of the East India Company’s ships, kept the crew of his own ship in perfect health by lemon-juice, while the crews of the accompanying ships were so disabled that he had to send his own men on board to set sails. In 1636, this remedy was again recommended in medical works on scurvy. Admiral Wagner, commanding our fleet in the Baltic in 1726, once more showed it to be a specific.  John Woodall, in 1628, used lemon-juice for the treatment of scurvy, and gave a full description in his ‘ Viaticum, being the Pathway to the Surgeon’s Chest’ (1628). “ The virtues of orange juice for scurvy dates back to 1671, when Venette, considered orange and lemon juice contained ‘ something which was directly opposed to the causes of scurvy,’ cited by Browning (1931). ‘ Vitamins’ : Special Report Series No. 167 (1932) : Medical Research Council, London, contains an interesting account of the experience of Lind (1747).  Lind had twelve scurvy patients on his hands on board the “Salisbury” at sea, on the 20th May, 1747. ‘ They all in general had putrid gums, the spots, and lassitude, with weakness of the knees ………….and had one diet common to all, viz., water-gruel sweetened with sugar in the morning, fresh mutton-broth often times for dinner, at other times light-puddings, boiled biscuit and sugar, etc., and for supper barley and raisins, rice and currants, sago and wine or the like.’ Lind treated two each of his patients with (1) cyder, (2) elixir vitriol, (3) vinegar, (4) sea-water, (5) an electary composed of garlic, mustard seed, radaphan, balsam of Peru, and gum myrrh, and (6) ‘two oranges and one lemon given them every day.’ Supplies of oranges and lemons lasted for six days. ‘ The consequence was, that the most sudden and visible good effects were perceived from the use of oranges and lemons; one of those who had taken them being at the end of six days fit for duty. The spots were not indeed quite off his body, nor his gums sound; but, without any other medicine, than a gargarism of elixir vitriol, he became quite healthy before we came to Plymouth, which was on the 16th June. The other (on the orange and lemon ration) was the best recovered of any in his position, and, being deemed pretty well, was appointed nurse to the rest of the sick.’ ”  (historicalpapers.wits.ac.za)Since these early days of scurvy on land and sea, the juice of Citrus fruits has been always regarded as the more efficacious remedy, and modern science confirming their merits as the best and cheapest of anti-scorbutics. At sea, today, by an Order in Council (Statutory Rules and Orders, 1927, Merchant Shipping), provision is made for the issue of orange juice—concentrated orange juice containing not less than 70% of total solids—at the rate of I f fl. ozs. mixed with six times its volume of water.”  (historicalpapers.wits.ac.za)

References

Baird, D. K.,  Haworth, W. N., Herbert, R. W., Hirst, E. L., Smith, F. and Stacey, M..   Ascorbic acid and synthetic analogues.  J. Chem. Soc., 1934, 62-67, http://dx.doi.org/10.1039/JR9340000062.

Daniel, E. P., Munsell, H. E..  1937.  Vitamin Content of Foods.  United States Department of Agriculture.

Gutte, B.. (Ed)  1995.  Peptides: Synthesis, Structures, and Applications.  Academic Press.

Maurer, K. and Bruno Schiedt, B.. (August 2, 1933) “Die Darstellung einer Säure C6H8O6 aus Glucose, die in ihrer Reduktionskraft der Ascorbinsäure gleicht (Vorläuf. Mitteil.)” (The preparation of an acid C6H8O6 from glucose, which equals ascorbic acid in its reducing power (preliminary report)), Berichte der deutschen chemischen Gesellschaft66 (8): 1054-1057.  (http://onlinelibrary.wiley.com/doi/10.1002/cber.19330660807/pdf)

Maurer, K. and Schiedt, B.. (July 4, 1934) “Zur Darstellung des Iso-Vitamins C (d-Arabo-ascorbinsäure) (II. Mitteil.)” (On the preparation of iso-vitamin C (d-arabo-ascorbic acid) (2nd report)), Berichte der deutschen chemischen Gesellschaft67 (7) : 1239–1241

Takahashi, T.,  Mitsumoto, M. and Kayahori, H..  1960.  Production of D-Araboascorbic Acid by Penicillium.  Nature volume188pages411–412 (29 October 1960)

Takahashi, T.,  Mitsumoto, M. and Kayahori, H..  1960.  The Production of D-Araboascorbic Acid by a Mold.  Bull. Agr. Chem. Soc. Japan, Vol. 24, No. 5, p. 533 – 534, 1960.

Dr R. Walker, Professor of Food Science, Department of Biochemistry, University of Surrey, England.

http://www.historicalpapers.wits.ac.za/inventories/inv_pdfo/AD1715/AD1715-9-1-11-002-jpeg.pdf

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