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Red hot chilli pepper in wooden bowl. Spicy food concept.

Portable device reveals heat of chilli peppers

Image credit: Tasipas/Dreamstime

Thai researchers have developed a portable device – whimsically shaped like a chilli pepper – that can assess how 'hot' a pepper will be by detecting how much capsaicin it contains.

Chilli peppers are a popular food ingredient around the world. But all types of chillis contain different levels of capsaicin. This is a compound that gives chilli peppers their kick and may give a palate-singeing burn to people not used to spicy foods.

In addition to imparting a spicy flavour, the capsaicin has several health benefits, including anti-oxidative, anti-carcinogenic and anti-inflammatory activities. Therefore, the demand for capsaicin as a food additive and a pharmaceutical agent is growing.

Professor Warakorn Limbut and his colleagues at Songkla University in Thailand wanted to develop a simple, accurate, and cheap method to quantify the capsaicin content of chilli peppers and food samples. Other methods that have been developed for this purpose are complicated, time-consuming, or require expensive, bulky instruments. 

The researchers made a portable device shaped like a small chilli pepper that could be connected to a smartphone to display the results of the analysis. The paper-based electrochemical sensor within the device consisted of graphene nanoplatelets doped with nitrogen atoms to improve their electrical conductivity.

A chili pepper-shaped device containing a paper-based electrochemical sensor can be connected to a smart phone to reveal how much capsaicin is in a hot pepper.

A chili pepper-shaped device containing a paper-based electrochemical sensor can be connected to a smart phone to reveal how much capsaicin is in a hot pepper.

Image credit: Adapted from ACS Applied Nano Materials 2020

When the team added a drop of diluted capsaicin to the sensor, the compound underwent oxidation and reduction reactions, producing an electrical current that the device detected. 

After optimising the sensor, the researchers used it to determine capsaicin concentrations in six dried chilli samples. They then added the chillis to an ethanol-containing solution, shook it up, and introduced a drop of the sample.

The researchers found that the device accurately measured capsaicin concentrations from 7.5-90 μM in the six samples, and could detect down to 0.37 μM in the diluted samples.

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