Stickers and a smartphone to facilitate denitrification

image: A new film reacts to nitrite anions with a color change, becoming darker with higher nitrite levels.
see After

Credit: Adapted from ACS Applied Materials & Interfaces 2022, DOI: 10.1021/acsami.2c09467

Nitrates and nitrites give processed meats their characteristic pink color and robust flavor. Although many consumers want to limit the consumption of these preservatives because the substances can form potentially carcinogenic compounds, it is difficult to determine the amount contained in a food. Today, researchers who report in Applied materials and ACS interfaces have developed a color-changing film that consumers can stick on food and easily analyze nitrite levels by taking a photo with a smartphone.

Cured and processed meats, such as salami and bacon, are often treated with nitrite or nitrate salts to make them look and taste fresh. Although nitrate is relatively stable, it can be converted into the more reactive nitrite ion in the body. When in the acidic environment of the stomach or under the high heat of a frying pan, nitrite can undergo a reaction to form nitrosamines, which have been linked to the development of various cancers. Some methods for determining nitrite levels in foods already exist, but they are not very consumer-friendly and often require expensive and labor-intensive techniques and instruments. To help consumers make more informed decisions, Saúl Vallejos, José M. García and their colleagues wanted to develop an easy-to-use nitrite quantification system.

To do this, the researchers developed a film they called “POLYSEN”, which means “polymer sensor”, composed of four monomers and hydrochloric acid. Discs cut from the material were placed on meat samples for 15 minutes, allowing the monomer units and acid from the film to react with the nitrite in a four-step azo coupling reaction. The discs were then removed and immersed in a sodium hydroxide solution for one minute to develop the color. When nitrite was present, the yellowish tint of the film increased with higher nitrite levels in the food. To quantify the color change, the researchers created a smartphone app that self-calibrates when an array of reference discs is photographed in the same image as the sample discs.

The team tested the film on meats prepared and treated with nitrite, in addition to store-bought meats, and found that the POLYSEN-based method produced results similar to those obtained with a traditional nitrite detection method and more complex. In addition, POLYSEN has complied with European regulations on the migration of substances from the film to food. The researchers say the new approach could be a user-friendly and inexpensive way for consumers to determine nitrite levels in food.

The authors acknowledge funding from the La Caixa Foundation and the Spanish Agencia Estatal de Investigación. They also acknowledge the support and collaboration of the Inforapps company.

The abstract of the article will be available on August 3, 2022 at 8 a.m. EST here: http://pubs.acs.org/doi/abs/10.1021/acsami.2c09467.

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