Activity to inhibit modori (a loss of elasticity of fish jelly occurring in the heating Process of kamaboko production) was examined in the extracts of various plant foodstuffs. Screening of the inhibitor was carried out by measuring the dose-dependent inhibitory effect of the extracts on the Boc-Leu-Thr-Arg-MCA degrading activity of modori-inducing protease optimally active at 50°C. Among 34 Plant foodstuffs tested, the extracts of spinach leaves, corn pepper fruits, potato tubers, red pepper fruits, eggplant fruits, bell pepper fruits, corn seeds, and kiwi fruits demonstrated dose-dependent inhibitory effects on the synthetic peptide-degrading activity of modori-inducing protease.
Among them, spinach leaf extract showed the most prominent inhibition of the modori phenom-enon when it was added to threadfin bream surimi which has a strong modori characteristic. SDS-PAGE analysis revealed that the moderi-inhibiting effect of spinach leaf extract would be due to the inhibitory effect on myosin heavy chain breakdown. The modori-inhibiting activity of spinach leaf extract was stable at 80°C, but was gradually lost when heated to 90°C. The molecular weight of the spinach leaf inhibitor was estimated to be less than 10, 000 by gel filtration.
