Nitrite quantification in processed meat using an enzyme biosensor, a portable reader and a smartphone: a facile and accurate approach

The control of nitrite levels in foodstuff is essential for ensuring human safety. However, the protocols are long and require lab equipment (spectrophotometer and centrifuge) not available in industrial or commercial settings. Herein, we adapted an electrochemical nitrite biosensor utilizing the enzyme cytochrome c nitrite reductase (ccNiR) previously developed in our lab, to meet the analytical requirements of cured meats, and validated it using real samples from different brands. The enzyme was immobilized on a disposable carbon screen-printed electrode (SPE) modified with multi-walled carbon nanotubes (MWCNTs) and connected to a hand-held potentiostat coupled to a smartphone. The carbon nanotubes suspension was optimized using chemically friendly solvents and the SPE surface was electrochemically characterized using ferricyanide as a redox probe, to fine-tune the modification formulation. The nitrite biosensor delivered a sensitivity of 0.0103 μA/μM, a linear range from 5 to 100 μM, and a lower detection limit (LOD) of 3.2 μM. Subsequently, the biosensor was tested for its ability to detect nitrites in various processed meat samples, considering factors such as type and origin. The validation of the electrochemical biosensor was conducted using the gold standard Griess method and HPLC, although the first one failed to detect nitrites in some samples due to matrix interferences. Accordingly, the nitrite biosensor performed well, providing highly accurate and precise results (smaller SD), even in non-centrifuged samples, making it possible to control the meat quality at any point of the chain distribution.