This study assessed the feasibility of developing a machine vision system equipped with ultraviolet (UV) light, using changes in fish-surface color to predict aerobic plate count (APC, a standard freshness indicator) during storage. The APC values were tested and images of the fish surface were taken when fish were stored at room temperature. Then, images' color-space conversion among RGB, HSV, and L*a*b* color spaces was carried out and analyzed. The results revealed that a* and b* values from the UV-light image decreased linearly during storage. A further regression analysis of these two parameters with APC value demonstrated a good exponential relationship between the a* value and the APC value (R 2 = 0.97), followed by the b* (R 2 = 0.85). Therefore, our results suggest that the change in color of the fish surface under UV light can be used to assess fish freshness during storage.

Red sea bream (Pagrus major) scale fluorescence characteristics were identified as a potential rapid and non-destructive means for assessing the fish's freshness. To investigate this, live red sea breams were purchased, slaughtered, and prior to measurement, stored at 22 ± 2 • C for 27 h. During subsequent storage, the K value of the dorsal meat-as a standard freshness indicator-along with front-face fluorescence spectra of representative dorsal scales, were measured simultaneously at 3 h intervals. Two major fluorescent peaks, A and B, were identified with excitation and emission wavelength pairs of 280/310 nm and 340/420 nm, which were mainly contributed to by tyrosine and collagen, respectively. Subsequent analysis showed that the fluorescence intensity ratio of peak B to A (I B /I A) increased linearly during storage (R 2 = 0.95) and is proposed as a potential non-destructive index of fish freshness. Thus, our results suggest that the fluorescence characteristics of fish scales can be used to assess fish carcass freshness during storage.

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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.