Abstract: The use of one-factor-at-a-time method in conjunction with response surface methodology was investigate to optimize the process parameters of ultrasonic-assisted bromelain treatment for tenderizing duck meat. Moreover, the mechanism underlying meat tenderization was explored. The optimized conditions were obtained as follows: temperature 45 ℃, pH 7.2; bromelain concentration, 350 U/g, ultrasonic power 80 W and tenderization time 15 min. Under these conditions, the predicted and measured shear force were 20.208 and 21.110 N, respectively. The tenderized meat presented a significant increase in pH, water-holding capacity and myofibrillar fragmentation index (MFI) and a significant decrease in shear force, myofibrillar protein solubility and insoluble collagen content compared with the untreated meat (P < 0.05), but the color was not significantly changed (P > 0.05). SDS-PAGE results indicated that macromolecular proteins of the treated duck muscle were hydrolyzed into small peptides and/or amino acids. Transmission electron microscopy (TEM) revealed that myofibrillar Z lines were broken and dissolved, sarcomeres were deformed and shortened, with the I and A bands becoming blurred, and myofibrillar fragmentation occurred. Ultrasonic-assisted bromelain treatment had a significant effect on tenderizing duck meat and greatly reduced the tenderization time, and the tenderized meat was juicy and elastic and had greatly improved quality.

Key words: ultrasonic-assisted, bromelain, duck muscle, tenderization, SDS-PAGE, ultrastructure