Freshness related fluorescent compound changes in Japanese dace fish (Tribolodon hakonensis) eye fluid during storage

The main fluorescent compounds in Japanese dace fish (Tribolodon hakonensis) eye fluid associated with freshness were distinguished and their time-dependent changes with storage were observed. For this experiment 95 fish were stored at 20 °C for 36 h, meat from the dorsal part was sampled at different storage times and used to measure K value, a standard freshness index. At the same time eye fluid was collected from the fish for fluorescence spectra acquisition and biochemical analysis. K value results showed the fish remained fresh up until 18 h of storage, and then deteriorated quickly thereafter. While aromatic proteins and amino acids were confirmed to be the main fluorescent compounds in eye fluid, they showed a complicated change during storage. Fluorescent compounds of uric acid, closely associated with freshness, had low intensity values at the start of storage, with values raising sharply later in storage; showing an exponential increase during storage. Dityrosine was found to be present only at a very late stage of storage. These results indicate the connection between specific fluorescent compound changes and the progression of storage could be employed as a meaningful predictor of fish freshness.