The term mustard oil is used for two different oils that are made from mustard seeds:
- a fatty vegetable oil resulting from pressing the seeds,
- an essential oil resulting from grinding the seeds, mixing them with water, and extracting the resulting volatile oil by distillation.
Mustard oil from pressed seeds
This oil has a strong smell, a little like strong cabbage, a hot nutty taste, and is much used for cooking in Bengal, Bihar and other areas of India and Bangladesh. The oil makes up about 30% of the mustard seeds. It can be produced from black mustard (Brassica nigra), brown Indian mustard (Brassica juncea), and white mustard (Brassica hirta).
Due to its high content of erucic acid, which is considered noxious, mustard oil is not considered suitable for human consumption in the United States, Canada and the European Union, although mustard oil with a low content of erucic acid is available. In India, mustard oil is generally heated almost to smoking before it is used for cooking; this may be an attempt to reduce the content of noxious substances, and does reduce the strong smell and taste.
In North India, mustard oil is also used for rub-downs and massages (see ayurveda). Massage with the oil is thought to improve blood circulation, muscular development and good texture to human skin; the oil is also antibacterial. To get around the restriction in Western countries, the oil is often sold "for external use only" in stores catering to Indian immigrants.
In India the restrictions on mustard oil are viewed as an attempt by foreign multi-national corporations to replace mustard oil with canola oil, a variety of rapeseed with a low erucic acid content. But for North Indians, mustard oil is not just a cooking medium but it is very much intricately interwoven with their culture. They have been using it for ages and dispute that there is enough evidence for the toxicity of erucic acid, instead maintaining that mustard oil is beneficial to human health because of its low content of saturated fats, ideal ratio of omega-3 and omega 6 fatty acids, content of antioxidants and vitamin E, as well as the fact that it is cold pressed (extracted at 45-50 degrees Celsius).
Mustard oil from mixing seeds with water
The pungent taste of the mustard condiment results when ground mustard seeds are mixed with water, vinegar, or other liquids (or when they are chewed). Under these conditions, a chemical reaction between the enzyme myrosinase and a glucosinolate known as sinigrin from the seeds of black mustard (Brassica nigra) or brown Indian mustard (Brassica juncea) leads to the production of allyl isothiocyanate. By distillation one can produce a very sharp tasting essential oil, sometimes called volatile oil of mustard, that contains more than 92% of allyl isothiocyanate. The white mustard Brassica hirta does not give allyl isothiocyanate, but a different and milder isothiocyanate.
Allyl isothiocyanate serves the plant as a defense against herbivores. Since it is harmful to the plant itself, it is stored in the harmless form of a glucosinolate, separate from the myrosinase enzyme. Once the herbivore chews the plant, the noxious allyl isothiocyanate is produced. Allyl isothiocyanate is also responsible for the pungent taste of horseradish and wasabi. It can be produced synthetically, and is sometimes known as synthetic mustard oil.
Because of the contained allyl isothiocyanate, this type of mustard oil is toxic and irritates the skin and mucous membranes. In very small amounts, it is often used by the food industry for flavoring. It is also used to repel cats and dogs, and to denature alcohol, making it unfit for human consumption to avoid the extra taxes collected on alcoholic beverages.
The CAS number of this type of mustard oil is 8007-40-7, and the CAS number of pure allyl isothiocyanate is 57-06-7.
- Canadian Food Inspection Agency
- Isolation of Erucic Acid from Mustard Seed Oil by Candida rugosa lipase
- The Mustard Seed Conspiracy by Vandana Shiva in The Ecologist, July 2001
- Tanuja Rastogi (2004) Diet and risk of ischemic heart disease in India. American Journal of Clinical Nutrition, Vol. 79, No. 4, 582-592, April 2004. Retrieved 2007-01-29