Differentiation between fresh and frozen-thawed sea bream (Sparus aurata) using impedance spectroscopy techniques

• The effect of freezing on sea bream quality was studied with impedance spectroscopy.
• Freezing process affected IMP, the TBA index, WHC and several textural parameters.
• The changes caused by the freezing process were detected using the double electrode.
• The arrow electrode could not discriminate between frozen-thawed and fresh fish.
• Impedance spectroscopy is an excellent tool to assess the damage on fish structure.

The aim of this study was to evaluate a rapid, low-cost and easy-to-use system of impedance spectroscopy with two different electrodes (double electrode (DE) and arrowhead (AH)) to distinguish between fresh and frozen-thawed sea bream. Samples of fresh sea bream and those submitted to freezing at − 18 °C and to 2 freezing cycles, kept in frozen storage for different periods of time, were evaluated. The freezing process did not affect moisture, pH, TVB-N, or the microbial quality. However, it provoked a slight degradation of IMP, a slight increase in the TBA index and a decrease of the WHC and several textural parameters. All these changes were detected with the impedance spectroscopy using the DE, which could differentiate fresh sea bream from frozen-thawed samples. However, the AH could not discriminate between the different types of samples. The frozen storage time (15, 30 or 60 days) did not have any effect on the microbial and physico-chemical parameters evaluated, or on the electrical properties of the muscle.Industrial relevanceTo prevent unfair competition by false labelling, differentiating between fresh fish or that which has previously been frozen is an important issue of authenticity in the seafood sector. The use of impedance spectroscopy could provide a new approach to the development of small and portable instruments for frozen-thawed fish detection. Impedance spectroscopy could be a promising method for industrial use, authorities and quality control. The present work evaluates a rapid, low cost and easy-to-use system, based on impedance spectroscopy in order to differentiate between fresh and frozen-thawed sea bream. This method could be applied during any stage of fish marketing, facilitating quality control activities and the detection of fraud in the fish sector.