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.