Researchers: Dr King Tong Lau, Alexis Pacquit, June Frisby.

In the fisheries industry, there is much interest in developing rapid methods to evaluate real-time freshness of fish and seafood products, particularly ones that reflect and account for the products history and their storage conditions at various points along the distribution chain from "harvest-to-home". Under EU directive 79/112/EEC, seafood (similar to other foodstuffs and pre-packed foods) must display either a "date of minimum durability" or, when considered highly perishable, a "use by date".
 
One convenient route to the development of a “smart package” sensor is to immobilise a chromoreactant dye that will indicate the presence of spoilage volatiles in the package headspace through visible color changes. This has led to the development of simple sensor spots prepared by entrapment of a pH indicator dye into a plasticised cellulose acetate or PVC matrix to form a fast response pH indicator based sensor. The dyes respond to the collective volatile amines, known as Total Volatile Basic Nitrogen (TVB-N), that are released during spoilage of samples.

 
The results obtained to date show that the dye based sensors respond well to the changing levels of TVB-N released by gradually spoiling fish samples. A number of different species have been analysed in collaboration with the Marine Institute of Ireland, such as cod, whiting, plaice, orange roughy and black scabbard. The former three are of great economic importance in the Irish Fisheries Market, and the latter two are newly-evaluated deepwater fish species that are slowly being introduced into the Irish markets. There is interest in the fish as substitutes for the more commonly used fish, which have strict quotas restricting numbers that can be caught, to aid the environmental problem of dwindling stocks.

Figure 1: Cardinal (above) and Roundnose Brigadier obtained from BIM marine officers on-board trawlers at Howth, Co. Dublin, Ireland.

The sensors change color during the experimental timeframe from yellow to purple, and this is monitored using a spectral imaging technique. Excellent results have been obtained from the sensors monitoring this wide variety, and manuscripts have been submitted to international journals detailing the results (awaiting acceptance). Additional results have been obtained by correlating the sensor results with the headspace TVB-N levels, determined by a titration method. Furthermore, excellent correlations to the sensor response were found by microbiological analysis of the fish samples. These results have also recently been submitted for publication.

Recent changes to the formulation offered increased sensitivity and stability. Latest results showed real time spoilage monitoring of more underutilised species (Fig. 1) evaluated for introduction to the Irish Market. Field trials in local supermarkets will soon be carried out.