The effects of gravading process on the nutritive value of rainbow trout (Oncorhynchus mykiss)

Abstract

Gravad trout is a low-processed product prepared by sprinkling fillets with a mixture of salt and sugar and subsequently placing them in cold storage. During the gravading process, there is some loss of nitrogenous substances to the brine, as well as changes in meat protein struc­ture, which was proved in the present study by the increase of available thiol groups and disul­fide bond content. Therefore, it is of interest to investigate whether the nutritive value of pro­teins is altered in the process, and both in vitro and in vivo studies of nutritive value were con­ducted. In vitro assays revealed that gravading of fish leads to an increase (about 5 %) in rela­tive total essential amino acid content compared to raw fish proteins. The chemical score (CS) and exogenous amino acids integrated index (EAA), calculated according to the FAO/WHO (1991) standard reference pattern, reached to maximum values equivalent to 100%. The gra­vad’s nutritive indices measured by the in vivo methods, namely biological value (BV) and net protein utilization (NPU), were close to those for steam cooked fish, but slightly worse than those for raw fish. True digestibility (TD) changes were verified as statistically insignificant.