Two different protein hydrolysates have been obtained from trout viscera using commercial enzymes and acid autolysis (silage) at pilot scale (3 x 75 kg per batch and 758 kg of viscera respectively).
While the enzymatic hydrolysis occurs in a few hours in controlled temperature and alkaline pH conditions, silage takes several days at room temperature in strong acidic conditions (pH between 3.5 and 4.0).

The hydrolysates achieved 54 and 49 % (D.M.) of free amino acids respectively. They  have been used in the formulation of biobased fertilisers (BBF) with potential bio-stimulant effect. The product formulated with the silage qualifies as organic fertiliser following EU Regulation and is being tested in field trials.

Oil content in rainbow trout viscera varies between 50 and 80% depending on the season. Maximum oil separation before the hydrolysis of the fish viscera is a key factor to improve the hydrolysis performance and to obtain a good quality fish oil as a valuable co-product in both, enzymatic hydrolysis and silage. Ambient temperature determines the duration of the autolysis, the time until the silage liquefies completely. While enzymatic hydrolysis is more efficient in producing FAA, silage can be a cost-efficient alternative. Shelf-life of the resulting bio stimulant products needs to be studied in deeper.

Enzymatic hydrolysis pilot (Source: BARNA).

Liquid BBF prototypes (Source: FERTINAGRO)

Fish viscera silage (Source: AZTI)