Optimization of the autolysis of rainbow trout viscera for amino acid release using response surface methodology

Aquaculture has grown exponentially during the last decades, even overcoming traditional fishing in volume since 2012 (Iñarra et al, 2018). The rise of the production of fish involves the rise of fish by-products, that in case of being disposed could suppose an environmental risk. Fish viscera are part of the by-products used to produce fishmeal and are the 10-18 % of the whole fish weight.
Fish silage or acid autolysis is commonly used in areas with high fisheries rates and consists of liquefaction and stabilization of minced fish at room temperature, normally adding formic acid until reaching a pH between 3.5 and 4.5 to prevent microbial growth. Hydrolysis of proteins occurs thanks to the endogenous acid proteases that are located at the fish viscera, which enable to get low molecular weight peptides and amino acids (Toppe et al, 2018). The resulting protein hydrolysates could be used as fertilisers. However, silage can take several days to achieve a high hydrolysis degree. In this work, autolysis has been carried out simulating the conditions of enzymatic hydrolysis but only working with the endogenous enzymes from fish viscera with the aim of accelerating a typical silage to get free amino acids while saving costs derived from the use of commercial enzymes.