Differentiating between fresh and frozen-thawed fish fillets by muscle fibre permeability measurement

Abstract

There is no comprehensive method for differentiating between fresh and frozen-thawed fish fillets. This is an ongoing problem, particularly in relation to regulations. In this study, we showed the relevance of using the properties of mitochondria to discriminate fresh fish fillets from frozen-thawed fish fillets. The use of red muscle fibres of Gilthead sea bream allowed us to leave mitochondria in their physiological environment and to avoid possible alterations of mitochondrial membranes during isolation steps. The impact of freezing on fillets was evaluated by measuring the permeability of fibres and mitochondrial membranes to nicotinamide adenine dinucleotide + hydrogen (NADH). NADH permeability of fresh fillet fibres stored at 4 °C was compared to the permeability of fibres extracted from frozen-thawed fillets. Two approaches were used to measure permeability changes: a spectrophotometric method that measured consumption of NADH by complex I, and an oxygraphic approach that measured stimulation of O2 consumption by NADH. Fibres from frozen-thawed fillets were more permeable to NADH and were less sensitive to the permeabilizer alamethicin. The sensitivity of this method allowed us to clearly detect red muscle fibres from frozen-thawed fish versus fresh fish fillets.