Changes in Umami-Enhancing Nucleotides in White Mullet (Ophiocephalus argus var. Kimnra) Meat Stored at Ice Temperature

The aim of this study was to investigate the effect of ice-temperature (IT) storage on the umami-enhancing nucleotide content in white mullet (<i>Ophiocephalus argus</i> var. Kimnra) meat. White mullet dorsal muscle was used as the raw material, and 4 °C chilled storage was used as a reference. After determining the ice temperature (-0.6 °C) of the dorsal muscle, the effect of IT storage on its umami-enhancing nucleotides was investigated. The umami nucleotide levels, physicochemical properties (pH, muscle color, water-holding capacity, and cooking loss rate), glycolytic metabolites (lactic acid, pyruvic acid, and glycogen), and enzyme activities (lactate dehydrogenase, pyruvate kinase, and 5'-nucleotidase) in the dorsal muscle were examined. The results indicate that IT storage significantly (<i>p</i> < 0.05) lowered pH while improving the water-holding capacity compared to 4 °C chilled storage. Both storage conditions showed an initial increase followed by a decrease in the inosine 5'-monophosphate (IMP) content, while the content of guanosine 5'-monophosphate (GMP) progressively declined. IT storage maintained significantly (<i>p</i> < 0.05) higher IMP and GMP levels than chilled storage in the late storage stage. The accumulation of the bitter taste substances hypoxanthine (Hx), lactic acid, and pyruvic acid was reduced under IT storage. These findings demonstrate that IT storage effectively inhibits the degradation of umami-enhancing nucleotides and is beneficial for preserving the meaty taste of white mullet meat.