Development of pH sensitive films for monitoring spoilage volatiles released into packaged fish headspace

Amines such as trimethylamine (TMA), dimethylamine (DMA) and NH ₃, collectively known as total volatile basic nitrogen (TVB-N), are released from fish during spoilage. Cresol red was successfully entrapped within a plasticised cellulose acetate matrix to produce sensors that could monitor the levels of TVB-N released from fish. The dye does not differentiate between the different bases that are released during spoilage but instead responds to any base capable of deprotonating it. Calibration of the sensors using a red light source and a monochrome digital camera suggested that a simple illumination source [such as a light emitting diode (LED)] and a detector (such as a photodiode) could be used to monitor colour changes in the sensors. The pK_a of the dye in the solid-phase dye coatings did not vary significantly from that in free solution. There was a linear relationship between the colour intensity of the dye at 573 nm and the log of the NH ₃ concentration in the headspace. Whiting, obtained from a local market and stored at room temperature, showed a definite and measurable increase in TVB-N levels between 24 and 30 h. Orange roughy and black scabbard, deepwater fish obtained under known conditions, showed a rise in TVB-N levels between 30 and 45 h when stored at room temperature. Samples stored on ice took 160 to 200 h to achieve similar levels of spoilage.