Tenderization of Yak Meat by the Combination of Papain and High-Pressure Processing Treatments

The effects of papain and high-pressure processing (HPP), applied separately or in combination, on the tenderization of yak meat were studied regarding texture, water-holding capacity (WHC), cooking loss (CL), pH, and color. When papain was used alone, both the papain concentration level and treatment time could affect the tenderization. The maximal shear force (MSF) of yak meat was decreased by 46.85% and the WHC was increased by 9.93% when 80 U/mL papain was injected into yak meat and then incubated at 55 °C for 120 min. However, the color was significantly deteriorated. When the HPP treatment was performed alone, the MSF of yak meat displayed an initial decrease followed by an increase as the processing pressure or treatment time rose. Although an improved tenderizing effect was achieved at 250 MPa/15 min, leading to a MSF decline of 49.27% and a WHC increase of 10.50%, the meat turned white. Applying treatment sequences of an HPP and papain combination can significantly influence the tenderization effect. Optimal tenderization was obtained by the injection of papain (80 U/mL) and incubation at 55 °C for 30 min followed by HPP at 50 MPa/15 min (Pap → HPP). Results from this process indicated that the MSF of yak meat was decreased by 46.30% and 50.27%, respectively, compared to the separate applications of both HPP (50 MPa/15 min) and papain (80 U/mL, 30 min) treatments. Meanwhile, no significant color change was detected. The microstructure of yak meat was analyzed following the application of different treatments. Results suggest that the meat treated with Pap → HPP exhibited larger spacing and more damaged cells than untreated meat or the sample subjected to other treatments. These findings provided a possible explanation for the specific tenderization result when exposed to the combined treatments.