Determination of the quality of frozen hake using its microwave dielectric properties

The work reported here examines the changes in microwave dielectric properties of south Atlantic hake (Merluccius capensis) during long-term frozen storage. Variables related to the dielectric properties of individual fish were measured in the microwave region using an open-ended coaxial sensor and time domain reflectometer. The multivariate data so obtained were subjected to principal component analysis both to eliminate colinearity of the data and to reduce the number of variables. The principal components (PCs) obtained were then used in multiple regressions to produce calibration equations for the prediction of a number of variables of interest e.g. time and temperature of storage and sensory attributes. Other data such as water holding capacity, texture (shear strength), apparent viscosity of homogenates and concentration of free formaldehyde were also used along with the dielectric data to improve the prediction of these variables. In addition, using the PCs as descriptors in discriminant analysis, the fish were sorted into defined groups, e.g. season of catching, quality. Discrimination was generally achieved with high success rates, the success rate of assigning Atlantic fish to the correct season of catching being higher than 92%.This study has been done using financial support from the Commission of the European Communities, Fifth Framework Programme, specific RTD programme Quality of Life and Management of Living Resources, project QLK1-2001-01643, ‘A New Method For Measurement Of The Quality Of Seafood’.Peer reviewe