New Perspectives in Science Education

Shio-koji is a traditional Japanese seasoning made from rice malt (koji) and contains multiple enzymes such as amylase and protease. In particular, protease breaks down proteins and helps tenderize meat and fish. In recent years, shio-koji has become widely used in households as a basic seasoning alongside miso, soy sauce, and mirin. However, some commercial products undergo heat sterilization during manufacturing, which can inactivate enzymes and reduce their protein-degrading activity[1].　Consequently, enzymatic activity varies greatly among products. In this study, three types of commercial shio-koji and one homemade shio-koji were compared and evaluated in terms of their protein-degrading abilities. Because it was uncertain whether the commercial products had been heat-treated, homemade shio-koji—which was confirmed to be unheated—was included for comparative analysis. Experiments were conducted using gelatin dissolution, protease activity assays, and pork tenderization tests[2]. In the gelatin experiment, differences in dissolution rates at different temperatures visually demonstrated variations in enzymatic activity. The protease activity assay quantitatively revealed enzyme levels, which sometimes differed from visual observations. In the pork experiment, the degree of tenderization varied depending on the product type and incubation temperature. These findings indicate that shio-koji exhibits measurable enzymatic activity that can be observed through simple experiments. Using fermented foods—familiar materials in daily life—as teaching tools allows students to intuitively understand enzyme function and temperature dependence. Connecting everyday experiences with scientific concepts can foster inquiry-based learning and deepen biochemical understanding, thereby contributing to science education.

Keywords:Shio-koji , Fermented food，Enzymatic activity，Inquiry-based learning

REFERENCES

​[1] …Maebashi, K., Nakata, M., Shimizu, S., & Seki, N. (2015). Effect of fermentation temperature on residual enzyme activity in shio-koji production. Nippon Shokuhin Kagaku Kogaku Kaishi (Journal of the Japanese Society for Food Science and Technology), 62(6), 290–296. https://doi.org/10.3136/nskkk.62.290

[2] …Abe, M., Sawayama, S., & Akita, O. (2018). Effects of soaking pork in shio-koji before cooking. Journal of Cookery Science of Japan, 51(3), 141–147.