NMR Approach for Monitoring Caranha Fish Meat Alterations due to the Freezing-Thawing Cycles

The fish meat shelf-life is highly influenced by temperature, making it necessary to use the cold chain to ensure freshness. Once this chain is stopped, unwanted reactions are initiated, and nutritional and texture changes in the meat may occur, compromising its consumption. Although these changes are important, it is not always possible for the consumer to differentiate between fresh and re-frozen fish due to the similarity when exposed to ice. In this context, the present study describes a metabolomic approach used to assess the influence on fish meat of the break in the cold chain by freezing-thawing cycles. Samples of caranha (Piaractus brachypomus) were used, and the metabolic profiles of frozen and frozen-thawed fishes were evaluated by nuclear magnetic resonance (NMR). The metabolic profile changes were identified through the chemometric treatment of NMR data and quantified using the Electronic Reference to Access In Vivo Concentrations (ERETIC 2) method. The results indicated the freezing-thawing cycles favored the increase of endogenous and exogenous enzymatic activities, expressed by variations in inosine, hypoxanthine, lactate, taurine, creatine, and trimethylamine amounts. This increase in metabolite concentrations, in particular inosine, hypoxanthine, and trimethylamine, was attributed as the main cause for the losses on fish meat quality and nutritional flavor, when compared with fresh fish.