Abstract: In an attempt to investigate the effects of different freezing pretreatments on the emulsification and gelation properties of myofibrillar protein (MP), this study aimed to analyze changes in the emulsifying activity index (EAI), emulsifying stability index (ESI), emulsion particle size, rheological properties, gel strength, cooking loss, water distribution and morphology of MP extracted from porcine Longissimus dorsi muscle pretreated by air freezing (AF), immersion freezing (IF) or ultrasonic-assisted immersion freezing (UIF). The results showed that AF and IF remarkably lowered the emulsifying activity and emulsion stability of MP compared with the control group (held at 4 ℃ for 6 h) and resulted in significantly larger and non-uniform sizes of emulsion droplets. UIF markedly increased the emulsifying activity but did not change the emulsion stability or droplet size. UIF improved the viscoelasticity and gel strength of heat-induced MP gels and reduced the cooking loss compared with the other treatment groups, and water distribution in the gel network was more uniform. high-resolution field-emission scanning electron microscopic (FE-SEM) observation revealed that the network structure of UIF-treated MP gels was more compact than that of the other treatment groups, closer to that of fresh MP gels. In summary, UIF-treated MP had better emulsification and gelation properties, indicating that UIF could maintain the processing quality of frozen meat better.

Key words: pork; ultrasound-assisted immersion freezing; myofibrillar protein; emulsifying characteristics; gel properties