Rapid test identifies adulterated sesame oil

Sesame oil bottleResearchers in China have developed a rapid analytical technique for sesame oil that could be used to guard against adulteration.

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 criminals who substitute it with low-value or illegal oils.

The team from Zhejiang University and the Chinese Academy of Sciences investigated the use of a technique called near infrared hyperspectral imaging (NIR-HSI) to satisfy what they say is an "urgent need" for a rapid, non-destructive way to test sesame oil.

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 and cannot be used for in-line identification in industrial production lines.

Conventional NIR spectroscopy - an analytical technique that detects specific molecules based on their absorption and reflection of light at near infrared wavelengths - has also been used to identify sesame oil. This captures average spectral information over an entire sample, but is less sensitive than NIR-HSI which produces images in which every pixel contains spectral data.

The small study examined four different sesame oil samples - Chinese varieties known as Huiyi, Liuyanghe, Taitaile and Xiaomo - and found that each could be distinguished from the other using NIR-HSI.

Glass dishes containing the oil could be scanned in just five milliseconds, suggesting the technique can be deployed at production line speeds.
NIR-HSI has also been used in the food industry to detect tiny contaminants that may be missed using other analytical methods, for example finding trace levels of peanuts that could pose a hazard to people with nut allergies.

The research is published in the open-access journal PLOS One.

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