1National Research Institute of Fisheries Science, Fisheries Research Agency, Yokohama, Kanagawa 236-8684, 2Department of Food Science and Human Wellness, Rakuno Gakuen University, Ebetsu, Hokkaido 069-8501, 3Food Research Institute, Toyama Prefectural Agricultural, Forestry & Fisheries Research Center, Yoshioka, Toyama 939-8153, 4Umekama Inc., Kainasaki, Toyama 939-3552, Japan
To clarify the pattern and process of protein degradation of fish sauce mashes containing salt and koji mold, and deepsea smelt Glossanodon semifasciatus or wastes from kamaboko processing, which have already been heated during the process of making kamaboko, the production of degradation products during fermentation was studied. The liquefaction ratio in deepsea smelt and wastes mash increased markedly during 7 days of fermentation. The insoluble protein content of both mashes also decreased rapidly with the liquefaction despite the difference in main material. These results suggest that the rapid protein degradation in both mashes at the early stage of fermentation could be caused by the koji mold rather than endogeneous digestive enzymes contained in viscera of fish. According to SDS-PAGE analysis, the disappearance of protein components and the production of low-molecular-weight components which could not be separated by 12.5% polyacrylamide gel during the fermentation period were different between the two mashes. Moreover, the content of free amino acids in deepsea smelt mash was higher than that in wastes mash. As a result, the production and accumulation of low-molecular-weight protein and free amino acids in fish sauce mash were affected by the characteristics of protein in the main material.