Development of a colorimetric sensor for monitoring of fish spoilage amines in packaging headspace

The development of an inexpensive "chemical bar-code", in the form of on-package sensor spots that monitor spoilage in fish and seafood products is described. The sensor contains a chromoreactant dye (pH sensitive) that indicates by a visible colour change the presence of volatile spoilage compounds such as trimethylamine (TMA), ammonia (NH₃) and dimethylamine (DMA) collectively known as total volatile basic nitrogen (TVB-N). Under EU directive 95/149/EEC, TVB-N analysis must be performed if sensory methods raise doubts about the freshness of seafood species. The response can be monitored with a simple, portable and inexpensive reflectance colorimeter that we have developed, based on LEDs and a photodetector. The choice of LED was to match the absorption band of the chosen dye. Trials on cod, whiting and under-utilised species (roundnose, brigadier and cardinal) enabled real time monitoring of their spoilage and the sensor responses were found to correlate to changing microbial populations.