Hydrolysis of surimi paste from walleye pollock (Theragra chalcogramma) by cysteine proteinase cathepsin L and effect of the proteinase inhibitor (E-64) on gelation

The gel strength of kamaboko obtained from walleye pollock (Theragra chalcogramma) was much reduced when the surimi paste was incubated at 60 °C for 2 h. The proteinase inhibitor, E-64, could enhance the gel strength and, at 200 μg/g of surimi, appeared to be the most effective. Amino acid analysis of the corresponding kamaboko showed that E-64 suppressed the release of peptides. Electrophoretograms revealed the inhibition of MHC degradation by E-64. Actomyosin was extracted and subjected to Sepharose 6B gel filtration to obtain the actomyosin non-binding cathepsin L (Lmix). Studies of substrate specificity and the effect of activators and inhibitors confirmed that the thiol–cysteine enzyme obtained was crude cathepsin L. Its high heat-stability indicated its strong hydrolytic ability. Lmix, at 0.6 unit/g of surimi, greatly decreased walleye pollock kamaboko gel strength from 112 to 27.8 g/cm2 when incubated at 60 °C for 2 h. The degradation was effectively inhibited by E-64 at 200 μg/g of surimi and the gel strength of the corresponding kamaboko was increased to 302 g/cm2. The above results suggested that cathepsin L contributed to the modori phenomena in kamaboko processed from walleye pollock surimi.