India, Sept. 1 -- If there is one item ubiquitous in grocery stores across cities and villages of India, it is mustard oil. For generations, people have used it for cooking and tempering food, as hair oil, even as a massage oil for toddlers and wrestlers. When consumers purchase the oil, they do so believing they have bought pure, unprocessed Indian mustard. But is that really the case?

The label on most mustard oil bottles provides percentages of unsaturated and saturated fats, claims about the purity of the oil and nutritional details. But the crucial information that almost always goes amiss is the variety of mustard used and the oil's erucic acid content.

Erucic acid is monounsaturated fatty acid that naturally occurs in the seeds o...