Direct contact ultrasound tempering of frozen pork: Effects on physicochemical properties, myofibrillar protein and microstructure.

Traditional ultrasound-assisted meat tempering usually adopts the water-immersion method, which requires water as a coupling medium and is inconvenient for application in most scenarios. Direct contact ultrasound tempering treatment was proposed to improve the tempering conveniency and retain the freshness of frozen meat products. In this study, the effects of water immersion ultrasound (WUT), direct contact ultrasound with water bag (CUTW), and direct contact ultrasound with ultrasonic couplant bag (CUTC) were compared with traditional air (AT) and water (WT) tempering on the tempering rate and quality of meat. The results demonstrated that, compared with conventional ultrasound methods, direct contact ultrasound tempering (CUTW) achieved comparable efficiency while avoiding the need for water immersion. CUTW produced the highest water-holding capacity (74.64 %) and the lowest cooking loss (25.26 %). It also reduced myofibrillar protein (MP) aggregation and oxidation during tempering, and caused less disruption to MP tertiary structures. Microstructural observations further revealed that muscle fibers in the CUTW-treated samples were denser and exhibited minimal damage. Overall, CUTW provides an effective alternative to immersion-based ultrasound tempering, offering similar or even improved quality outcomes without the inconvenience of water usage, making it more practical for household refrigerator applications.