Comparative study of muscle proteins in relation to the development of yake in three tropical tuna species yellowfin (Thunnus albacares), big eye (Thunnus obesus) and skipjack (Katsuwonus pelamis)

Burnt tuna (BT), or yake-niku, is a quality flaw of the muscle characterised by a pale colour and grainy and exudative texture. Cathepsin-L, water soluble and total protein components from normal and BT muscles, from three tropical tuna species - yellowfin (YFT, Thunnus albacares), bigeye (BET, Thunnus obesus) and skipjack (SKJ, Katsuwonus pelamis) - were compared by electrophoretic and western blot analyses to identify biomarkers for BT. As expected, SDS-PAGE patterns were species-specific but differences, due to BT, were observed only between some low ionic strength extracts of BET and YFT. Protein oxidation and cell proliferation analysed by immunoblotting did not show differences between BT and normal muscles. Gelatine zymography revealed different gelatinase activity patterns that, although not linked to BT, may affect the final texture of the muscle. A 43 kDa band, identified as creatine kinase by proteomic analysis, showed the potential to be a good indicator for BT in BET and YFT.