Tenderness of pork m. longissimus thoracis et lumborum after accelerated boning. Part II. Effect of post-slaughter ageing
Introduction
Accelerated boning of meat carcasses has been conducted for a number of years. Accelerated boning enables production costs to be reduced due to lower labour requirements, a reduction in chiller space and energy input and increased product turnover (Cross & Seideman, 1985, Powell et al., 1982). Accelerated boning of pork has been slow to be employed world wide, largely due to the logistics of changing to accelerated boning and also the potential detrimental impact on tenderness because of the rapid drop in muscle temperature that occurs when muscles are removed pre-rigor. Accelerated boning of pork loins followed by chilling at 0 °C results in cold toughening and higher drip loss (Rees, Trout, & Warner, 2001b). Furthermore, other researchers have also observed cold toughening of pork following accelerated boning (Cross & Seideman, 1985, Honikel & Reagan, 1987). Thus, alterations to the accelerated boning methods used for pork are required to overcome the problem of cold shortening and reduced proteolytic activity, the two factors that contribute to cold toughening. Dransfield, Jones, and MacFie (1980–1981) have shown post slaughter ageing can also be used to overcome increased toughness. The experiment in this study was designed to determine the rate of ageing of accelerated boned pork.
A method reported to improve meat tenderness is post slaughter ageing of the muscle (Dransfield et al., 1980–1981). However conflicting reports are presented on the ideal storage time and whether post slaughter storage of cold shortened muscle is effective in improving tenderness.
Meat becomes more tender during storage post rigor (Dransfield et al., 1980–1981), a process referred to as ageing. Tenderisation is believed to occur because of the degradation of some of the key structural proteins (desmin, titin and nebulin) by endogenous enzymes when meat is aged (Koohmaraie, Wheeler, & Shackelford, 1995). Furthermore, changes in the sarcoplasmic proteins, actomyosin and connective tissue have been observed during ageing along with myofibrillar fragmentation that occurs in or near the z disc (Bandman & Zdaris, 1988, Koohmaraie, 1994). This fragmentation has been related to increased tenderness (Bandman & Zdaris, 1988, Koohmaraie, 1994).
There are differing views on the optimum time of post mortem ageing to achieve pork tenderness following conventional boning. Harrison, Bowlers, Anderson, Tuma, and Kropf (1970) and Buchter and Zeuthen (1971) observed an increase in tenderness in pork LTL muscle up to the sixth and eighth days post mortem respectively. In contrast, Bennett, Bramblett, Aberle, and Harrington (1973) found that ageing more than one to two days did not significantly improve the tenderness of pork. Furthermore, Feldhusen and Kuhne (1992) found that the optimum shear force values were attained after two to three days of ageing. Dransfield et al. (1980–1981) used a model to predict that on average 50% of the tenderisation of pork occurs in two days relative to 4.2 days for beef and veal under their experimental conditions.
Conflicting views are presented in the literature on the degree of ageing of meat following accelerated boning. The lack of improvement in tenderness with post slaughter storage of muscle following accelerated boning is believed to be due to cold toughening. Davey, Kuttel, and Gilbert (1967) demonstrated that with increased muscle shortening the muscle demonstrates a decrease in tenderness improvements with ageing. The reduced tenderness improvement when muscles shorten is believed to be caused by structural changes in the myofibrils preventing the proteolysis by endogenous enzymes of proteins on or near the z line (Iversen, Henckel, Larsen, Monllao, & Moller, 1995). It is possible that the tougher muscle resulting from accelerated boning may require longer to reach its optimal tenderness. Therefore a closer examination of the rate of ageing is required.
Thus this experiment was designed to test the following hypotheses:
- 1.
muscles undergoing accelerated boning and chilling at 0 °C will not age due to cold shortening and a reduction in proteolytic activity
- 2.
muscles undergoing accelerated boning and chilling at 14 °C will tenderise rapidly due to the prevention of cold shortening and maximisation of proteolysis
- 3.
muscles undergoing rigor boning will undergo rapid ageing (80% of the improvements in tenderness within 4 days post slaughter) as previously observed in Rees et al. (2001b).
Section snippets
Methodology
Fifteen Large White × Landrace female pigs were slaughtered on three separate days following stunning with carbon dioxide (90% CO2 in air for 1.8 mm) and after splitting the carcass the sides were randomly allocated to one of three treatments:
- 1.
RB—rigor boning, placed in the chiller and boned at rigor;
- 2.
AB-0—accelerated boning within 0.5 hours of slaughter and placed in an ice water bath (0 °C) until rigor; and
- 3.
AB-14—accelerated boning within 0.5 hours of slaughter and temperature conditioned at
Rate of pH and temperature decline
The rates of pH and temperature decline for the three treatments can be seen in Fig. 1, Fig. 2, respectively. At 30 min, 1, 2, 4, 5, 6,7, 8 and 9 h post slaughter there was no difference in muscle pH between the three treatments (P>0.05). At 3 h post slaughter, the AB-0 muscles had a higher muscle pH than the AB-14 and RB muscles (<0.01). At 30 min post slaughter, no difference in muscle temperature was observed (P>0.05). By 1 h post slaughter and continuing to rigor, the AB-0 muscles had a
Discussion
Improvements in meat tenderness have been reported with post slaughter ageing. The tenderisation of meat occurs in two stages—an initial rapid phase followed by a slow phase (Takahashi, 1996). The rapid improvement in tenderness is mainly due to the structural weakening of myofibrils which begins at rigor mortis where tenderness is at its lowest. The slow improvement is due to the structural weakening of the endomysium and perimysium (Takahashi, 1996). However, when severe cold shortening
Conclusions
Post slaughter storage of pork appears to be effective at improving tenderness when severe chilling conditions are prevented. Under conditions that could result in cold shortening, ageing was prevented due to the shortening of the sarcomeres preventing proteolysis from occurring. As the AB-0 muscles did not appear to have completely entered rigor morris at initial sampling as indicated by the higher muscle pH, the true impact of this treatment on sarcomere length may have been missed.
Acknowledgements
The authors wish to acknowledge the financial assistance of the Pig Research and Development Corporation, Canberra, Australia and the assistance of D. D'Souza, P. Walker, C. Hofmeyr, H. Channon, M. Kerr, A. Payne, R. Biden, P. Weston and K. Butler.
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