Hardening of Salmon Egg Products Made from Fresh and Frozen Eggs

Abstract

“Ikura,” a seasoned salmon roe product in Japan, is produced mainly from eggs of the chum salmon caught during spawning migration. Owing to the high volumes of salmon caught during peak season, appropriate storage and processing methods are essential to maintaining egg quality. We investigated the processing properties of fresh or frozen-thawed salmon eggs at different maturity levels, focusing on hardening during storage. Our results confirmed that little hardening during storage occurred in eggs in the skein state in the abdominal cavity with a low maturity level, whereas substantial hardening occurred in the individual egg grains in the peritoneal cavity. Similar results were obtained using fresh and frozen salmon eggs, and the hardening of matured salmon eggs depended on the storage time and temperature. Based on SDS-solubility and SDS-PAGE analyses, the macromolecularization of egg membrane proteins occurred during egg hardening. The frozen eggs tended to harden faster than fresh eggs, and the hardening pattern was slightly different between these eggs; these differences may be explained by various factors, such as protein polymerization and degradation. The hardening of the egg membrane progressed after salting, and this phenomenon is likely to occur during salting and aging in industrial manufacturing.