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We analyzed the volatile basic nitrogen content, pH, total viable cell count, and biogenic amine contents in chub mackerel (Scomber japonicus) stored at 5 and 25°C to examine changes in freshness. Among the various parameters, we found the volatile basic nitrogen content had the highest correlation with cadaverine content (r2 = 0.72 to 0.88). We also tried to measure cadaverine contents at different times during storage by using near-infrared (NIR) spectroscopy. However, because of the high water content in the fish, we could not obtain meaningful results. Next, we prepared samples for NIR spectroscopy by dilution with 0.1 N HCl, ultrafiltration (3 or 10 kDa) with a glass filter, and dehydration. The samples prepared with the 3-kDa filter had peaks in the NIR spectra between 1,379.3 and 1,388.9 nm, and those prepared with the 10-kDa filter had peaks in the spectra between 1,897.3 and 1,898.6 nm. The correlation coefficient (r2) between the NIR spectroscopy and high-performance liquid chromatography with cadaverine results was 0.98 to 0.99. We concluded that the biogenic amine content could be used to evaluate freshness in fish products, and that NIR measurements could be used to rapidly and accurately determine freshness.

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In the present work, we used threadfin bream (Nemipterus spp.) surimi fish cakes to test the viability of freeze-dried Ecklonia cava hot water extract (ECWE) as a gel enhancer. The effects of freeze-dried ECWE on the gel strength and the colour of the fish cakes were investigated. The gel strength increased in fish cakes incorporated with 0.5% freeze-dried ECWE as compared to the control (no ECWE). The lightness and whiteness values of samples containing ECWE were lower than those of the control samples. Scanning electron microscopy (SEM) observations of fish cakes containing 0.5% freeze-dried ECWE exhibited a finer and more continuous matrix as compared to the control samples. Incorporating 0.5% ECWE improved the gel strength, and produced high-quality emulsions with a finely distributed gel network due to the presence of mannitol and some polyphenolic compounds in freeze-dried ECWE. The use of freeze-dried ECWE in the production of fish cakes is effective as a natural gel enhancer for surimi-based products.