Colorimetric sensor based on a poly(ortho-phenylenediamine-co-aniline) copolymer for the monitoring of tilapia (Orechromis niloticus) freshness

[Display omitted] •The copolymer changes color by effect of the presence of amine vapors due to deprotonation.•The colorimetric sensor is used to detect the freshness of tilapia in real time.•After 48 h of storage under refrigeration at 10 °C the fillets are no longer fit for human consumption. For monitoring tilapia (Orechromis niloticus) freshness degree, a colorimetric method based on a copolymer of ortho-phenylenediamine and aniline, in a molar ratio of 1 to 1, was developed. The optical sensor changes color as a function of pH, therefore, it is sensitive to the presence of alkaline vapors such as the volatile amines (TVB-N) produced during fish spoilage. A kinetic approach was used to correlate the copolymer (sensor) response to the presence of ammonia, dimethylamine, and trimethylamine vapors, which are the main products generated by the bacteria during fish spoilage. The levels of TVB-N and microbial growth patterns (Pseudomonas spp), in specimens of tilapia fillets stored under refrigeration at 10 °C, correlated well with the color change of the copolymer, showing that after 48 h the specimen was no longer fit for human consumption.