A scientific team at the Instituto de Investigaciones Marinas de Vigo has developed a methodology to predict the shelf-life of oily fish. The new method can be applied shortly after fish have been caught and before it is processed or frozen. It will optimize the use of fish catches, which is essential now that global stocks are becoming smaller.

Fresh oily fish.The earliest spoilage stage in oily fish is rancidity, caused by fat oxidation which is easily noticed for a characteristic rancid smell. This is a process that can’t be prevented even if the fish is frozen. Nevertheless, knowing the fish composition, it is possible to predict when this process will occur.

Spanish scientists from the Instituto de Investigaciones Marinas de Vigo of CSIC have obtained a method to predict the shelf-life of oily fish.

The methodology analyses different components (for fish, unsaturated fats, oxidants such as low molecular weight iron and hemoglobin or antioxidants such as ascorbic acid and tocopherol). Then, it compares these results to hydro-peroxides level and rancidity with the kinetic constants of fat oxidation processes.

A circumstance that makes this method interesting is that shelf-life of fish depends not only on what the species are but also on when fish have been caught. Scientists Rodrigo Maestre, Manuel Pazos e Isabel Medina, explain that “shelf life of fish depends on the moment when it have been caught because their composition has a high seasonal variability which is directly related to their stability”.

After being caught and until it arrives to the final costumer, fish go through different stages such as freezing, processing, canning or packing. Knowing fish shelf-life will enable companies to decide the best final use of the catches and to ensure a final product in perfect conditions.

Also, it makes possible to know the minimum amount of antioxidants required to preserve the product, thereby reducing the antioxidants applied.

This analytical methodology has been developed mainly for oily fish but can be also applied to other food products that suffer rancidity. It has been created for being applied in a lab. Nevertheless, scientists think that in the future it could be developed a portable kit for analyzing in situ, in the same place where fish have been caught.

Until now, methods to establish the shelf-life of fish have been based on predicting the growth of spoiling micro-organisms. But they are unsuitable for oily or semi-oily fish in which oxidative rancidity is predominant and occurs earlier than microbial spoilage.

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