NIR hyperspectral imaging accurately detects peanut contamination

The statement ‘May contain peanuts’ is so ubiquitous on food labels that it can seem rather meaningless to some allergy sufferers. What if there was a way to tell definitively whether or not a product contains traces of peanut, and at exactly what concentration?

A novel form of near-infrared (NIR) spectroscopy known as NIR hyperspectral imaging (HSI) could help clear up the uncertainty around peanut allergen labelling, researchers say. This analytical technique detects specific molecules based on their absorption and reflection of light at near-infrared wavelengths.

Scientists have already shown that peanut powder generates different NIR spectra to various other powdered foodstuffs, allowing any contamination to be detected.

Conventional NIR spectroscopy collects an average NIR spectrum over a large area, meaning that trace peanut contamination may be missed. A team of researchers from Spain and France decided to try to solve this problem using NIR HSI, which produces images in which every pixel contains spectral data.

Each pixel can thus contain information about peanut contamination, making NIR HSI much more sensitive than conventional NIR spectroscopy and allowing it to detect trace levels of peanut over a large area.

As a first test, the team of scientists confirmed that peanut powder generates different NIR spectra to wheat flour when analysed by NIR HSI, allowing the two powders to be distinguished from each other.

Next, they developed a scoring system that could determine whether or not specific pixels in an image of wheat flour contained peanut powder from their NIR spectra. Using this scoring system, they could then estimate the level of contamination by simply determining the percentage of pixels that contained peanut powder.

They tested this system on samples of wheat flour spiked with powder from four different types of peanut, including raw, blanched and roasted, at concentrations varying between 0.01% and 10%. The system was able to detect peanut contamination even at 0.01%, although it could only accurately determine the level of contamination at between 0.1% and 10%.

“These results show the feasibility of using HSI systems for detecting traces of peanut and similar products that are present in low percentages in powder foods with contrasting spectra,” said lead researcher Puneet Mishra from the Universidad Politécnica de Madrid in Spain.

The researchers are now working to apply the technique to detect contamination by other nuts, which can also cause serious allergic reactions.

The research was published in the Journal of Near Infrared Spectroscopy.