The Effect Of Freezing In Different Ageing Times During Post-Mortem On The Quality Of Thawed Lamb Loins

The research focused on the effect of freezing in different ageing times during post-mortem on the quality of thawed mutton.The research analyzed the rigor,rigor-off and aging time,and the variation of meat quality during post-mortem firstly.Based on the above results,mutton was frozen at different times including pre-rigor,rigor in the process and rigor-off and thawed in the same condition.The effect of freezing in different ageing times during post-mortem on the quality of thawed mutton was analyzed by detecting meat tenderization,color,water hold capacity(WHC),muscle contraction,protein degradation and glycolysis.The aim of this study was to provide theoretical support for meat products industry and to improve the quality of the thawed meat and reduce the water loss.(1)This part focused on physicochemical characters on rigor and ageing process during post-mortem of lamb loins.Seven indicators,that is pH values,ATP content,sarcomere length,shear force,myofibril fragmentation index(MFI),protein degradation and μ-calpain activity,were determined.From muscle to meat,pH value decreased then increased gradually which reached the ultimate value at 1 d post-mortem.Shear force value increased then decreased which was up to the maximum at 1 d after slaughter.Sarcomere length shortened firstly then became elongate gradually which was down to the minimum at 1 d and 2 d.ATP content increased then decreased.The 80 kDa subunit of μ-calpain degraded until vanished at 1 d,78 kDa subunit formed firstly then degraded completely at 2 d after slaughter.Desmin and troponin T were as the substrate of μ-calpain during ageing,which changed significantly and intact protein could scarcely not be observed at 7 d after slaughter.As a whole,longissimus dorsi initiated rigor from 2 h,and up to 1 d which got the largest extent and began rigor off after 2 d,when tenderness improved greatly in the process.(2)This part focused on the effect of freezing in different ageing times during post-mortem on the quality of thawed mutton based on the results of first part,and the control group was stored at 4℃.The frozen groups were frozen at 0,2,12,24,and 48 h post-mortem,and tenderness,WHC,color,color stability and muscle contraction were measured at different time points.Compared to the control group,pH values and color of frozen groups were significantly lower at the end of display.Based on the results in WHC and shear force values,12-24 h post-mortem was the appropriate freezing point.Based on the results of ultrastructure and sarcomere length,the meat quality was closed to the control by freezing at 12-24 h postmortem.In conclusion,12-24 h is the appropriate freezing time.(3)The analysis of the effect of freezing on the thawed meat quality was focused on two key pathways(protein degradation,glycolysis).Troponin T and desmin degradation,hexokinase,pyruvate kinase and lactic acid content were detected.Compared to the control,enzymatic activity reduced but lactic acid content increased of frozen treatments,which suggested that enzymatic activity was not the reason for glycolysis.After thawing,the sarcoplasmic reticulum was destroyed,and μ-calpain was activated earlier by accelerating release of Ca2+ leading to the higher degree degradation of desmin and troponin T.In conclusion,protein degradation is the main factor of variation of tenderness and water holding capacity in thawed meat.