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Detect nitrites with a smartphone? Colour-changing film developed to check nitrite levels in cured meat

Nitrite is a common preservative used in processed meat products. It provides a characteristic pinkish colour and fresh meat flavour to products such as York ham or mortadella.

However, nitrite is a contentious ingredient, having been directly associated to gastrointestinal tumours, stomach cancer, and the so-called blue baby syndrome.

In 2015, the International Agency for Research on Cancer (IARC) classified processed meat, including deli meats, as carcinogenic due to its links with – among other things – higher risk of colon cancer.

In Spain, researchers at the Universidad de Burgos have observed that consumers are increasingly interested in the presence of nitrites in their food products.

Given that current nitrite analysing tools available to consumers are complicated and laborious to use, the scientists have developed an alternative method: all you need is a sticker and a smartphone.

In a study published in ACS Applied Materials & Interfaces​ and funded by La Caixa Foundation and the Spanish Agencia Estatal de Investigación, the researchers detail their development of a colour-changing film that consumers can stick onto foods. Using a smartphone, consumers then take a picture of the film and ‘easily’ analyse nitrite levels.

The technology is founded on a sensory polymer sensitive to nitrite anions, which they’ve coined POLYSEN, as a colorimetric sensory film for the visual detection of nitrite.

The film is stuck onto the food surface of 15 minutes and then immersed in a basic sodium hydroxide solution for one minute. Colour changes are registered with a smartphone camera. The searchers have developed a smartphone app, ‘Colorimetric Titration’, which automatically autocalibrates the measurement, analyses the data, and outputs a nitrite concentration result to the user.

When nitrite is present, the film’s yellowish hue deepens: the darker the hue, the higher the concentration of nitrites in the food.

“In short, the novelty of our proposal for analysing nitrite in meat lies in the combination of [several] characteristics,” ​explain the study authors.

These include a costless novel sensory material, an easy experimental procedure, self-calibrated measurement, and a novel smartphone app that allows in situ measurement that can easily be used by the average person.

The invention is timely, given increased government interest in nitrate and nitrite levels.

Earlier this year, the Commission adopted a proposal to reduce the authorised levels of nitrates and nitrites in meat products. This year has also seen France’s National Assembly back a principle of ‘lower the trajectory’ of maximum levels of nitrates​ that can be added to characterise meats.

And in the UK, scientists and MPs are pushing for a ban​ on the use of nitrites in bacon.

Source: ACS Applied Materials & Interfaces

‘Easy Nitrate Analysis of Processed Meat and Colorimetric Polymer Sensors and a Smartphone App’

Published 3 August 2022

DOI: https://doi.org/10.1021/acsami.2c09467

Authors: Marta Guembe-García, Lara González-Ceballos, Ana Arnaiz, Miguel A. Fernández-Muiño, M. Teresa Sancho, Sandra M. Osés, Saturnino Ibeas, Jordi Rovira, Beatriz Melero, Cesar Represa, José M. García, and Saúl Vallejos.

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