Headspace test can spot adulterated sesame oil

 A quick and simple lab technique can help detect adulteration of sesame oil, a high-value edible oil used widely in Chinese and southeast Asian cuisine.

The technique – known as headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS) – was able to distinguish between genuine samples of sesame oils acquired from food vendors in Wuhan, China, and mock counterfeits created by mixing sesame oil essence into other, lower-cost oils such as soy, cottonseed and rapeseed.

Thanks to its popularity as a flavour enhancer and as an ingredient added to foods to impart health benefits sesame oil is generally priced at a premium to other edible vegetable oils and as a result has been targeted by fraudsters.

At the moment sesame oil is usually identified using a combination of physical and chemical tests which - while accurate - are time-consuming, inefficient and destroy the sample.

"Economically motivated adulteration for sesame oils has emerged around the world and [has become] a challenge for…public health," according to the scientists behind the work.

"Therefore, it is necessary to develop an effective detection method for the adulteration of sesame oil," they add.

GC-IMS is an increasingly used technique for the separation and sensitive detection of volatile organic compounds from samples, becoming popular due to fast response times, high sensitivity, ease of operation and low cost.

Measuring the volatile compounds in the air above the liquid in an oil container acts a bit like an electronic nose. In contrast, other techniques like NIR or MIR spectroscopy act more like electronic tongues because the sample has to be measured in liquid form.

The researchers – from China – combined HS-GC-IMS with chemometric methods to analyse and characterise the genuine and fake oils, and discovered that the composition of the fakes tends to be simple with fewer compounds compared with the authentic oils.

They found that main volatile components of counterfeit sesame oils are pyrazines, and identified a series of compounds that could be used as markers for mixtures of other oils with sesame essence that could be detected using other techniques such as gas chromatography (GC) and GC-MS.

"Taking these markers as targets, rapid and high-effective adulteration detection methods could be developed by designing electronic nose sensors," according to the scientists. The research is published in the journal Food Chemistry.