Application of simultaneous ultrasonic curing on pork (Longissimus dorsi): Mass transport of NaCl, physical characteristics, and microstructure

•Simultaneous ultrasonic (SIU) accelerated NaCl transport in porcine tissue.•The SIU with 20 + 40 + 60 kHz was the best to improve the texture properties.•The myoglobin oxygenation level did not change significantly after SIU curing.•The application of SIU could enlarge the extra-myofibrillar space in the pork. This study aimed to investigate the effect of ultrasound curing with various working modes and frequency combinations, including mono-, dual- and tri-frequency, on the content of NaCl and tenderness of pork loins (Longissimus dorsi). The physical qualities, myoglobin, moisture migration, distribution, and microstructure of pork were also evaluated. The results displayed that the NaCl content of samples cured by simultaneous ultrasound (100 W/L) working mode with a frequency combination of 20, 40, and 60 kHz was higher than that of other ultrasound working modes. The effect of ultrasonic brining was significantly better than the static curing when the saline solution was >35 mL. In addition, the samples cured by simultaneous ultrasound had better physical qualities, including more pickling absorptivity, less cooking loss, and lower hardness, tenderness, and chewiness value. The intensity of lightness was reduced, although redness and yellowness remained unaltered compared to static curing. The myoglobin content decreased drastically without changing the oxygenation level, and the relaxation time of T2b and T21 was delayed. The microstructure indicated that the ultrasonic treatment could promote changes in meat texture. Overall, the simultaneous ultrasound at various frequencies could efficiently accelerate NaCl penetration and improve pork quality.