Evaluating Nepal's Roasted Mustard Oil - Chromatography Explores

Khokana is a small village with a population of under 5000 that is located a few miles south of Kathmandu in central Nepal. It is a simple Newari village, people who are the historical inhabitants of Kathmandu valley and its surrounding areas. They have a culture and lifestyle that is different from other areas of the Himalayan foothills. But what Khokana is really known for is its mustard oil. It was even nominated for the world heritage list by UNESCO for the ‘living heritage’ associated with its roasted mustard oil.

Roasted mustard oil is a vegetable oil that has many professed health benefits. But there is little research into the composition and properties of different mustard oils from Khokana. In a paper - Chemical Profiling of Roasted Mustard Oils of Khokana, Nepal - published in the Asian Journal of Applied Chemistry Research, researchers from Tribhuvan University, Nepal investigated the detailed chemical composition of roasted mustard oils from Khokana.

Living museum to Newar identity

Roasted mustard oil many medicinal uses in Nepal. New-born babies, cholesterol and blood-pressure are all treated with roasted mustard oil. It is used from birth to death to purify and treat ailments, it is also used in religious rituals. In Khokana, the oil mill is part of a living museum showcasing Newar civilization – it is an important part of Newar culture, tradition, ethnic identity, and uniqueness. Hence the UNESCO nomination in 1996.

There are around 40 different varieties of mustard plants, but the most common ones used in oils are black mustard (Brassica nigra L.), Oriental or brown (B. juncea L.), and white or yellow mustard (B. hirta). The oil is obtained from mustard seeds which are first powered using a heavy wooden beam, the powered seeds are then roasted before being crushed with the oil collected. The oil is naturally dark coloured because of carotenoids and chlorophyll. Lipase enzymes affect the taste and aroma of the oils by breaking the ester bonds present in the oils. The oil is usually consumed without any further processing after the oil extraction. Mustard oil pungency is due to allyl isothiocyanate which is unique to mustard oil compared with other vegetable oils.

Determine the composition the chromatography way

The researchers behind the paper referenced above analysed mustard oil produced from local mills in Khokana. The oils analysed were produced from brown, black and yellow mustard seeds. The oils were analysed using gas chromatography-mass spectrometry. The use of GC-MS to analyse food samples is discussed in the article, Analysis and Identification of Mezcal and Tequila Aromas by Ambient Ionisation MS, GC-MS, and GCxGC-MS.

The researchers found that in one sample, the black mustard seeds from India, the main compound was cis-Oleic acid. In the other two samples the main compound was Erucic acid. The analysis the team carried out provided the fatty acid profile of mustard seed oils and the variation in fatty acids.