Radio Frequency Tempering Of Brined Thunnus Albacares And Its Quality Evaluation

The freezing and tempering processes have a direct impact on the quality of fish products.As one of the novel food tempering techniques,RF tempering has promising application possibilities due to its high tempering efficiency and homogeneity,and it has been widely employed for tempering meat and meat products.The effects of different freezing rates（0.35 and 0.47 cm/h）and different tempering rates（0.5,1.0 and1.5℃/min）on the quality of thunnus albacares were investigated using frozen tuna,comparing tempering rates,uniformity of tempering temperature distribution,tempering losses,color,lipid oxidation（TBARS）,total volatile base nitrogen（TVB-N）,and muscle microstructure（SEM）.The results showed that the two freezing rates had no significant effect on the quality of tuna（p>0.05）,while the different tempering rates had a significant effect on the quality of tuna（p<0.05）.The texture and microstructure analysis revealed that the least change in quality characteristics at the tempering rate of 0.5℃/min,while the samples showed more water loss and muscle tissue destruction at the tempering rates of 1.0℃/min and 1.5℃/min.The results indicated that the best product quality could be achieved when the freezing rate was0.47 cm/h and the tempering rate was 0.5℃/min for tempering large tuna blocks.Proper beining of fish products can improve water retention and enhance their unique flavour.However,before brining can be carried out,the brining transfer process needs to be investigated and analysed.In this study,the mass transfer kinetics of different concentrations of NaCl（2.5,5,7.5 and 10%（w/w））on tuna during static and ultrosound brining were evaluated.The results showed that both increasing NaCl concentrations and the application of ultrasound accelerated the diffusion of NaCl in the tuna muscle,with the highest yields obtained for the samples in the 5%concentration solution.Furthermore,the kinetic parameter values were significantly influenced by the NaCl concentration and ultrasonic application.The values of mass transfer kinetic parameters（k₁,k₂）for total content and water content changes during the brining process decreased with increasing NaCl concentration.In contrast,the higher the NaCl concentration,the greater the value of the kinetic parameter（k₁,k₂）for NaCl content change.Based on Fick’s second law,a one-dimensional diffusion model based on a semi-infinite plate in contact with a finite volume and fully stirred solution was developed for the curing process of tuna samples,and the effective diffusion coefficient（De）of NaCl was calculated.The application of ultrasound during the brining process increased the effective diffusion coefficient of NaCl from 402.8%to653.21%,with the highest De value for NaCl in a 5%NaCl solution.Moreover,ultrosound brining improved the uniformity of NaCl distribution,increased water holding capacity and reduced hardness and chewiness,but had no significant effect on the colour.The findings indicate that ultrasound can be a promising technique to accelerate the brining process of meat products and these results have direct implications for the quality management of brined meat products.Tuna products undergo several transit times before they are sold and consumed,during which temperature changes lead to an increase in the number of freeze-thaw cycles.The effects of repeated freezing and tempering on the quality characteristics and histological changes of tuna with different brining methods（static brining and ultrosound brining）were investigated using brined tuna.The tuna was subjected to 1,3and 5 freeze-thaw cycles in different brining methods,and the tempering rate,tempering loss,water holding capacity,p H,lipid oxidation（TBARS）,total volatile base nitrogen（TVB-N）,colour,moisture distribution and tissue microstructure were analysed.The results showed that the tempering time of brined tuna was significantly greater than that of unbrined tuna,but there was no significant difference between the two brining methods.After three freeze-thaw cycles,water holding capacity,p H,L*and a*values decreased significantly（p<0.05）,tempering losses,while TBARS,TVB-N and b*values increased significantly（p<0.05）.In addition,the degree of lipid oxidation was accelerated by brining and ultrasound application as the number of freeze-thaw cycles increased,with no significant differences in other relevant indicators between the two brining methods.Low-field NMR results showed enhanced water mobility in tuna.Low temperature scanning electron microscopy results showed that after three freeze-thaw cycles,the intracellular spaces began to increase in the unbrined samples,while the brined samples were able to maintain good myofibre structure and the thickness of myofibres was greater in the ultrasonic brined samples than in the static brined ones.The results suggest that repeated freeze-tempering can lead to a reduction in the quality of tuna,but that brined tuna can maintain good quality characteristics for no more than three freeze-thaw cycles.