Colour changing film for easy nitrite detection in foods

Researchers offer an inexpensive way for consumers to determine nitrite levels in foods

Nitrates and nitrites give processed meats their characteristic pink color and robust flavor. Although many consumers want to limit consumption of these preservatives because the substances can form potentially cancer-causing compounds, knowing how much is in a food has been difficult to determine. Now, researchers in Europe have developed a colour-changing film that consumers can stick onto foods and easily analyse nitrite levels by snapping a picture with a smartphone.

The researchers have developed a film they called “POLYSEN,” which stands for “polymeric sensor,” made of four monomers and hydrochloric acid. Disks punched from the material were placed on meat samples for 15 minutes, allowing the monomer units and acid in the film to react with nitrite in a four-step azo coupling reaction. The disks were then removed and dipped in a sodium hydroxide solution for one minute to develop the colour. When nitrite was present, the film’s yellowish hue deepened with higher nitrite levels in the food. To quantitate the colour change, the researchers created a smartphone app that self-calibrates when a chart of reference disks is photographed in the same image as the sample disks.

The team tested the film on meats they 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 and more complex nitrite detection method. In addition, POLYSEN complied with a European regulation for migration of substances from the film to the food. The researchers say the new approach could be a user-friendly and inexpensive way for consumers to determine nitrite levels in foods.