The Potential of Freshwater Fish Viscus from Silver Carp Hypophthalmichthys molitrix for Trypsin Source

Purpose Silver carp is widely cultured in China (the product reached 3.5 million ton per year), and approximately 20% of the non-edible viscera are discarded. Utilization of the viscera leads to a reduction in waste. Our previous study showed that silver carp produced two types of myosin isoforms, thermostable myosin in summer and unstable one in winter, for the adaptation of the environmental changes. Therefore, in this study, we purified trypsins from silver carp in summer and winter samples to investigate their thermostabilities. Methods Trypsins from summer and winter samples were purified by a series of chromatographies. The temperature dependence of trypsins was determined at pH 8.0 in the range of 20-80 degrees C, and the effect of temperature on the thermostability was determined by measuring the remaining activity after the incubation at pH 8.0 for 15 min in the range of 20-75 degrees C. Results From the summer sample, two trypsins (SSC-T1 and SSC-T2) were purified 63- and 72-fold with the yields of 24 and 21%, respectively, and a trypsin (WSC-T) was purified 81-fold with a yield of 40% from the winter sample. SSC-T1, SSC-T2 and WSC-T showed the same enzymatic characteristics, especially their optimum temperature (65 degrees C) and thermostability (stable below 63 degrees C in 15-min incubation) were similar to mammalian trypsins. Additionally, all were stable at 30 degrees C for 8 h in the presence of calcium-ion. Conclusion These data indicated the silver carp viscus has a potential for thermostable trypsin source all the year round. [GRAPHICS] .