Evaluation of fish freshness by physical measurement techniques

During storage of fish, changes in microbiological and chemical composition take place. This will alter the fish flesh structure and colour. Several physical measurement techniques exists to measure these changes. Texture measurements have shown to correlate with sensory analysis in some cases, but still there is no universal recommended method for assessing mechanical. Microstructural characterisation is another technique used to study structural changes during storage time or related to processing methods. Colour measurements are important in food quality control, but the link between colour and storage time is not established and therefore this method can not be used with today's methodology. Changes in colour is observed during storage, but can be caused by chemistry, temperature or rigor mortis. Due to chemical changes the electrical properties also change. Three different instruments are available to measure electrical properties; the Torrymeter, the Intelectron Fishtester and the RT-Freshness Grader. The use in fillets is limited to a few days, as' high salt contents in water ice and mechanically damaged fish cause erroneous results. A new method is spectroscopy, which now provides promising results. Preliminary tests on ice stored cod shows good correlation between measured spectra and days on ice. But there is still more testing that has to be done before this technique can be adopted by the industry. To label products Time-Temperature Indicators have been introduced. They cannot measure freshness, but can be used as indicators of freshness.