Fig. 1: Separation of oil by decantation from trout viscera.

When obtaining biofertilizers from fish viscera, one of the first aspects to take into account is their high oil content. In the case of rainbow trout (Oncorhynchus mykiss), the oil content of the viscera can reach up to 60% of its fresh weight.  In the experiments that have been carried out, it has been observed that the higher the oil content, the lower the yield of biofertilizer obtained. Therefore, it is necessary to separate as much oil as possible in a step prior to the hydrolysis reactions.

The quality of the separated oil influences its selling price as a valuable coproduct and therefore the economic feasibility of obtaining biofertilizers from fish viscera.

To ensure that the physico-chemical parameters of the separated oil are adequate, it is necessary:

  • Avoid, as far as possible, the contact of digestive enzymes with the separated oil.
  • Keep the viscera in refrigerated conditions (+4°C).
  • Reduce as much as possible the waiting time for processing.

Considering these aspects, we will achieve adequate oil quality values that will allow us to market the oil without additional processes.

Fig 2: Oil separated from whole, refrigerated viscera. FFA (Free Faty Acid): 2.7%. Peroxides: 3.5 meqO2/kg  —-   Fig. 3: Oil separated from broken, refrigerated viscera. FFA (Free Fatty Acid): 19 % Peroxides: 9,8 meqO2/kg