Erucic acid

Erucic acid is a monounsaturated omega-9 fatty acid, denoted 22:1 ω-9. It is prevalent in rapeseed, wallflower seed, and mustard seed, making up 40 to 50 percent of their oils. Erucic acid is also known as cis-13-docosenoic acid and the trans isomer is known as brassidic acid.

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Uses

It has many of the same uses as mineral oils but with the advantage that it is more readily bio-degradable. Its high tolerance to temperature makes it suitable for transmission oil. Its ability to polymerize and dry means it can be - and is - used as a binder for oil paints. Erucic acid will readily form many organic compounds. Adding this ability to its polymerizing characteristics makes it very suitable for use as organic matrices that need to be polymeric. This makes it especially useful in the manufacture of emulsions to coat photographic films and papers. A complex cocktail of many different erucic acid compounds are commonly used in just one roll of color film. It is widely used to produce emollients, especially for skin and healthcare products. Like other fatty acids, it gets converted into surfactants. Erucic acid is especially valued in tribology as a superior lubricant. When used in the manufacture of plastic films in the form of erucamide, it migrates to the surfaces and so resists the sticking of each film to its neighbor. Being a hydrocarbon of high calorific value, with a very low flash point, high cetane rating, and good lubrication qualities, erucic acid can be a valuable component of bio-diesel. When converted into behenyl alcohol (CH₃(CH₂)₂₁OH), erucic acid has many further uses such as a pour point depressant, enabling liquids to flow at a lower temperature and silver behenate for use in photography.^[1]

Sources of erucic acid

  It is produced naturally (together with other fatty acids) across a great range of green plants, but especially so in members of the brassica family. It is highest in some of the rapeseed varieties of brassicas, kale and mustard being some of the highest, followed by Brussels spouts and broccoli. For industrial purposes, a High-Erucic Acid Rapeseed (HEAR) has been developed. These cultivars can yield 40% to 60% of the total oil recovered as erucic acid.

Metabolism of erucic acid

Erucic acid is broken down in the human body by enzymes (long-chain acyl-coenzyme A (CoA) dehydrogenase) produced in the liver, which chop it into shorter-chain fatty acids, which are, in turn, broken down. For more information on this see: Lipid metabolism. Based on animal studies in adult pigs and piglets, it can be reasonably presumed that, in human infants that have not yet been weaned, these particular enzymes are in short supply (as the mother's milk is the normal food source during this period), although not totally absent. ^[2][3] Because of this, babies should not be given foods high in erucic acid. Before low-erucic acid oil rapeseed (LEAR & Canola) cultivars were developed, this situation was unlikely to present a realistic danger since erucic acid occurs in nature only along with bitter-tasting compounds that infants instinctively reject. In some of the new varieties, the bitterness or pungency has been considerably reduced to make it more palatable to humans and cattle. Studies on rats have shown that they are less able to digest vegetable fats (whether or not they contain erucic acid) than humans and pigs.^[4][5][6] Chariton et al. suggests: “Inefficient activation of erucic acid to erucyl-CoA and a low level of activity of triglyceride lipase and enzymes of betaoxidation for erucic acid probably contribute to the accumulation and retention of cardiac lipid.”^[7] Before this process was fully understood, however, there developed a misunderstanding, which continues to be repeated until this day. See below.

Health effects

No negative health effects have ever been documented in humans, although it is advisable not to give un-weaned babies foods containing erucic acid for the reasons given above.^{[8] [9]}

Epidemiological studies suggest that, in regions where mustard oil is still used in a traditional manner, mustard oil may afford some protection against cardiovascular diseases. In this sense 'traditional' means that the (a) oil is used fresh and (b) vegetable fats count only as a small percentage of the total caloric intake. Whether this effect is due to the nature of erucic acid per se to make the blood platelets less sticky, or to the presence of a reasonably high percentage of α-linolenic acid, or to a combination of properties of fresh unrefined oil, is as yet uncertain. Care needs to be taken with such epidemiological studies in order to exclude the possibility of early deaths from other causes skewing the results. The fact that early nonsymptomatic coronary disease is readily detectable post mortem and is absent in the mustard oil cohorts tends to add weight to the hypothesis that mustard oil is protective. ^[10]

A four-to-one mixture of erucic acid and oleic acid constitutes Lorenzo's oil; an experimental treatment for a rare neurobiology disorder adrenoleukodystrophy.

The high percentage of erucic acid in mustard oil has led to its being banned for food use in the European Union and other countries.

Health concerns

Before genetic engineering, plant breeders were aiming to produce a less-bitter-tasting multi-purpose oil from rapeseed that would appeal to a larger market by making it more palatable for cattle and other livestock. While it was possible to breed out much of the pungent-tasting glucosinolates, one of the dominant erucic acid genes would get stripped out of the genome as well, greatly reducing its valuable erucic acid content. Studies on rats show lipodosis problems when fed high quantities of erucic acid, however, so this did not hinder saleability.^[11] Later trials showed that rats had the same problems with other vegetable fatty acids, ^[12] because rats are poor at metabolising some fats.^[13] The plant breeding industry later changed "low erucic acid" to be its unique selling proposition over that of its competitors.

Thalidomide poisoning showed the importance and value of good human epidemiological studies over that of animal studies. There are not many studies done on humans with erucic acid; the majority are carried out by the food science industry on animals. Animal studies failed to show negative events occurring from feeding of erucic acid, and the studies were repeated under more and more unnatural scenarios. In one case, neonate piglets that have a limited ability to absorb these fats had their normal sow's milk replaced solely with rapeseed oil for one hundred percent of their calorific needs.^[14] The studies showed that lipidoses suffered by the piglets proved to be only a transient effect; the liver automatically responded by increasing enzyme levels to cope with the unusual diet, and the lipidoses subsided.

A recent study recorded the higher rates of lung cancer in countries with populations that cook over solid fuel wood and biomass fires and stoves. The possibility of production of smoke from heated oil was also considered, and it was established that rapeseed oil, which contains erucic acid, can cause increased lung carcinomas through emissions under high heat. However, the report also showed a variety of cooking oils also did this at similar heats. ^[15]

Cardiac concerns

The levels of erucic acid in human foods are restricted, in part, over concerns that it may adversely affect heart tissue.^[8] It promotes myocardial lesions in several animal models, including adult rats.^{[16] [17]} Choline and inositol offer some protection against this damage,^[16] while alpha-linolenic acid may aggravate it.^[18] Erucic acid is preferentially absorbed in myocardium tissue^[19] but is not metabolized there.^[17]

References

See also

• Lorenzo's oil