Effects of Freezing and Radio Frequency Tempering on Quality Characteristics of Marinated Yellow-Fin Tuna (Thunnus Albacares)

Temperature fluctuation is recognized as a significant factor contributing to the degradation of frozen fish quality. In this study, we investigated the impact of freeze—radio frequency (RF) temper cycles on various quality attributes, including color, microstructure, and water retention and distribution in tuna meat. We compared traditional static marination with ultrasonic-assisted marination following 1, 3, and 5 freeze-temper cycles, employing both refrigeration and RF tempering methods. Our findings revealed that RF tempering substantially reduced the tempering duration while maintaining temperature uniformity. After the initial 3 freeze-temper cycles, significant decreases were observed in tempering loss, water holding capacity, pH, L* and a* values of the samples (p < 0.05), concomitant with significant increases in thiobarbituric acid-reactive substances (TBARS), total volatile base nitrogen (TVB-N), and b* value (p < 0.05). Low-field NMR analysis indicated enhanced water mobility in tuna after the first 3 freeze-temper cycles. Scanning electron microscopy (SEM) images further suggested that the intracellular space in unmarinated samples expanded following 3 freeze-temper cycles, whereas marinated samples maintained better muscle fiber structure. Additionally, the thickness of muscle fibers in ultrasonically marinated samples exceeded that of the statically marinated cones. Hence, repetitive freeze-temper cycles resulted in a gradual decline in the quality of tuna. Nevertheless, marinated tuna retained favorable quality characteristics throughout the freeze-temper cycles, with the exception of the TBARS and b* value increase.