Thomas McKeon
USDA-ARS Western Regional Research Center, Albany, CA, USA
Over the years, a number of plants have been proposed as new crops for production of oils that would be useful for industrial applications. While many of these crops remain interesting as targets for improvement by agronomists or gene sources to be cannibalized by molecular biologists, none are broadly cultivated. On the other hand, old standby industrial oil crops including tung, rape, linseed, coconut and castor continue as commodity crops and have experienced increasing interest due to policies promoting biobased products.
The castor plant (Ricinus communis L.) has been used for industrial purposes as long as 22,000 years, with later uses of the castor oil in soap, lubricants, medication and fuel spanning thousands of years. More recently castor oil has been used additionally in synthetic surfactants, plasticizers, drying oils, cosmetics, and a variety of polymers. Most of these uses are a result of the unique nature of castor oil, which is composed of 90% ricinoleate, 12-hydroxy oleate. The mid-chain hydroxy group is susceptible to a range of chemical modifications including polymerization to polyurethane, and degradative reactions that lead to amino-undecylenate and sebacic acid, sources of polyamides and polyesters. Moreover, as a crop, the castor plant can achieve productivity as high as 2.5 tons of oil per hectare, provide adequate yields on marginal land or when dry-cropped. Yet castor remains a minor contributor among commodity oils, with world production just over 500,000 tons annually. The main deterrent to widespread cultivation is the presence of the protein toxin ricin, a potential threat agent and problem for processors in handling a biohazard. While alternatives to the castor plant are still under consideration, the presence of ricin in castor seed meal can be dealt with in several ways. Adoption of these approaches should lead to broader cultivation of the castor plant.