Lipid of the Month

Each month we highlight a lipid of scientific interest. The LIPID MAPS® Lipid of the Month Archive lists lipids highlighted from 2015 - present.

June 2021

Lipid of the month Ricinolein

On a warm summer evening at Old Warden airfield, England, the faint smell of June’s Lipid of the Month lingers in the still air. It comes from the engines of several antique, but still air-worthy, aeroplanes.

In the early years of the 20th century, castor oil, pressed from seeds of the castor oil plant Ricinus communis, was found to be a good lubricant for rotary aircraft engines1. Ricinolein is the main component, forming up to 90% of the oil. Ricinolein is a triglyceride of ricinoleic acid, a fatty acid chemically similar to oleic acid but with the addition of a hydroxyl group at the 12 position. It’s likely these hydroxyls, together with the homogeneity of castor oil, confer the properties that make it a much better lubricant than other vegetable oils.

Over time, hot ricinolein will polymerise and could ‘gum up’ an engine, but as rotary engines either burn or eject all of their oil, it is never in the engine long enough for gumming up to be an issue. So successful were the castor-containing lubricants developed and sold by the Wakefield Oil Company, it changed its name to an abbreviation of castor oil, and Castrol sells motor oils to this day.

Ricinolein has many more uses; it’s found in paints, cosmetics, inks and more widely in the chemical industry. It’s even suggested to be a renewable resource for other chemicals which can be derived from it2.

Castor oil is also probably most notorious for its laxative properties. Ricinoleic acid mimics prostaglandin E2 to stimulate smooth muscle contraction in the gut3. It is widely said that the continuous ejection of castor oil from aircraft engines had a laxative effect on the First World War pilots sitting behind those engines, but solid evidence for this is surprisingly difficult to find.

References

  • A History of Aircraft Piston Engine Lubricants
    West Coast International Meeting and Exposition
    DOI 10.4271/810849
  • Castor oil as a renewable resource for the chemical industry
    Eur. J. Lipid Sci. Technol. 2010
    DOI 10.1002/ejlt.200900138
  • Castor oil induces laxation and uterus contraction via ricinoleic acid activating prostaglandin EP3 receptors
    Proc Natl Acad Sci U S A.
    DOI 10.1073/pnas.1201627109

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