Effect Of Rapid Chilling On The Water-holding Capacity Of Pork

Nowadays,pig carcasses are usually chilled immediately after slaughtering in modern slaughterhouse to inhibit microorganism growth.There are two main chilling methods in modern slaughterhouse including conventional chilling(CC)and rapid chilling(RC).Conventional chilling(CC)requires carcasses to be chilled in cooling room of 4℃ for 24 h,while RC has a precooling procedure at temperature of-20℃ to-40℃ for 1 to 3 h before carcasses are put at 4℃ chilling room for the rest of 24 h.The rates of temperature and pH decline of pork carcasses after slaughtering are key factors to the subsequent meat quality during postmortem aging.Previous researches about rapid chilling have mainly focused on the effect on the quality of pork.While the different changes of muscle protein properties during postmortem aging are key factors to contribute to the different water holding capacity of pork,there were no reports about this kind of study.Thus,the purpose of current research was to explore the effect and mechanism of rapid chilling on the water holding capacity of pork.1.Effect of rapid chilling on the quality of pork longissimus dorsi(LD)Twelve six-month-old commercial crossbred pigs were slaughtered according to conventional slaughter procedure.After pigs were slaughtered,twelve carcasses were randomly assigned into two chilling groups.For RC,six carcasses were chilled at-20℃ for first 1.5 h and followed by chilling at 4℃ until 24 h postmortem.For CC,six carcasses were chilled at 4℃ until 24 h postmortem.RC significantly accelerated the rate of temperature decline of pork LD during early chilling process(P<0.01)and increased pH values at 1.5 and 8 h(P<0.05).Samples from RC had a significant lower purge loss compared to CC group at 1,4 and 7 d postmortem(P<0.05).RC could not affect centrifuge loss and cooking loss during postmortem aging.There was no significant difference about meat colour between two treatments.Samples of RC showed a higher proportion of immobilized water along with a lower proportion of free water compared to that of CC group during postmortem aging(P<0.05).2.Effect of rapid chilling on the rate of glycolysis of pork LD RC significantly slowed down the consumption of glycogen and ATP of pork LD at 1.5 h during chilling process(P<0.01).After chilling for 1.5,3 and 12 h,RC samples had a significant lower accumulation of lactate compared to that of CC samples at corresponding cooling time(P<0.05).When the carcasses were chilled for 24 h,there were no significant differences about the content of glycogen,lactate and ATP between two treatments.RC could not significantly affect the activity of HK,LDH and ATPase compared to that of CC treatment.3.Effect of rapid chilling on the protein properties of pork LD during postmortem agingRC could significantly decrease the denaturation of myosin and sarcoplasmic proteins of pork LD at 1,4 and 7 d postmortem(P<0.05).RC samples showed significantly higher solubility of sarcoplasmic and salt-soluble proteins compared to that of CC samples during postmortem aging(P<0.05).There were no significant differences about the rate of troponin-T and titin degradation between two chilling groups.Through the observations of electron microscopy,RC samples had a significant longer sarcomere length compared to that of CC treatment(P<0.05).