Iriko, boiled and dried sardines, are known as a food rich in calcium, but the calcium in iriko is mainly insoluble form, calcium phosphate. The purpose of this study was to examine the cooking method to promote the solubilization of calcium in iriko. In this study, iriko from Suou-Oshima Island, Yamaguchi Prefecture was used. We used four types, Chirimen (4 cm), Kaeri (5 cm), Koba (7 cm), and Ohba (9 cm). In the calcium solubilization test, 5 g of vinegar, citrus juice or vinegared miso was added to 5 g Iriko. After mixed and stood for a while, they were homogenized and centrifuged, the obtained supernatant was calcified at 550 °C. The ash was solubilized with 1% hydrochloric acid and the calcium concentration was measured by atomic absorption method. Even though the size or preparation method of soup stock from iriko was changed, almost no calcium was contained in the soup stock, and it was comparable to that of kelp soup. After adding vinegar or Nagato-Yuzukichi citrus juice and leaving for 30 minutes, the calcium solubilization rate from the small size Chirimen was higher than the other sizes of iriko. Assuming a Yamaguchi prefectural traditional dish "Chisha -namasu" (a dish which mixed chisha lettuce and vinegaredmiso with iriko), the calcium solubilization rate from iriko mixed with miso with or without vineger or Nagato-Yuzukichi juice was measured. The calcium solubilization rate from iriko was 3 times higher with vinegered miso, and 4 times higher with Nagato-Yuzukichi juice miso compared to that of miso only. But the calcium solubilization rate from iriko with miso was lower than the treatment with vinegar or Nagato-Yuzukichi juice only.
