Preparation of ISHIRU (Fish Sauce) by a Quick Ripening Process and Changes in the Composition of Amino Acids, Oligopeptides and Organic Acids during Processing

Abstract

IKA-ISHIRU or IWASHI-ISHIRU, fish sauce made from either squid liver or sardine with salt, have been produced in Noto peninsula of Ishikawa prefecture. But the long ripening period (about 1 or 2 years) is required to produce these ISHIRU with good quality. In this study, IKA-ISHIRU and IWASHI-ISHIRU were prepared by a quick ripening process (warmed method, 30-50°C). Changes in the composition of some chemical components of the two types of ISHIRU during processing were investigated. In the case of IKA-ISHIRU, the production speed of total nitrogen and free amino acids increased with an increase in temperature, whereas in the case of IWASHI-ISHIRU, a maximal production speed was obtained at 40°C. These ISHIRU contained large amounts of free alanine, lysine, glutamic acid, glycine, serine and valine. The oligopeptides that mainly consisted of glutamic acid, glycine, aspartic acid and proline existed in both IKA-ISHIRU and IWASHI-ISHIRU at all temperatures, and the oligopeptide content of IWASHI-ISHIRU was higher than that of IKA-ISHIRU. The contents of organic acids except pyroglutamic acid did not show any significant difference in this method. In the quick ripening process, IKA-ISHIRU and IWASHI-ISHIRU could be prepared for 24 days at 50°C and 38 days at 40°C, respectively.