The influence of the rate of pH decline on the rate of ageing for pork. II: Interaction with chilling temperature

doi:10.1016/S0309-1740(02)00285-1

Meat Science

Volume 65, Issue 2, October 2003, Pages 805-818

https://doi.org/10.1016/S0309-1740(02)00285-1 Get rights and content

Abstract

The influence of the rate of pH decline post slaughter on the rate of ageing of pork m. longissimus thoracis et lomborum was investigated. The rate of pH decline on 24 finisher pigs was manipulated by altering the method of stunning (carbon dioxide or electrical head to heart) and by the use of electrical stimulation (none or low voltage electrical stimulation (LVES) at 4 min post slaughter for either 15 s or 60 s). The rate of temperature decline was altered by chilling at 2 or 14 °C until rigor. The pH and temperature decline rates generated were designed to induce cold shortening at one extreme and protein denaturation at the other. The research results showed that the rate of pH decline was increased by electrical stimulation which in turn reduced cold shortening and improved tenderness. Chilling at 14 °C reduced the time to reach rigor by 1.3 h and resulted in a faster aging rate as indicated by a larger percentage change in WBSF from rigor to 4 days postmortem relative to carcases chilled at 2 °C. The greater tenderising effect appeared to be due to a combination of prevention of cold shortening and increased proteolysis. However, chilling slowly at 14 °C or the use of LVES for 60 s or any combination of these treatments did not induce protein denaturation.

Introduction

Variations in temperature and pH decline post slaughter are believed to influence the rate of ageing of pork muscle post slaughter. In paper (I) we investigated the influence of pH decline rate on the rate of ageing of pork and the impact of pelvic suspension on improving post-slaughter tenderness. It was hypothesised that a fast rate of pH decline with a slow decline in muscle temperature will result in protein denaturation thereby preventing improvements in tenderness with post slaughter storage. It was also hypothesised that a slow rate of pH decline with a fast decline in muscle temperature will result in cold toughening thereby preventing improvements in tenderness with post slaughter storage. The final hypothesis was that an intermediate rate of pH and temperature decline will prevent protein denaturation and cold toughening and promote proteolytic activity thereby resulting in improvements in tenderness with post slaughter storage.

The aim of the experiment was to investigate the effect of the rate of pH and temperature decline in pork carcasses on the rate of change in tenderness with post slaughter storage.

Section snippets

Methodology

Twenty-four male Large White×Landrace finisher pigs were slaughtered over three slaughter days and randomly allocated to one of four treatments designed to alter the rate of pH decline. The average live weight of the pigs was 89.4±22.67 kg. This resulted in an average carcass weight of 64.6±18.14 kg and a fat depth at the P₂ site of 19.7±6.9 mm. The stunning treatments were either electrical stunning using head to heart tongs (E, 1.3 amps for 4 s with variable voltage) or carbon dioxide

Results

No sides could be classified as DFD while 6 sides could be classified as PSE [n=2—stimulated for 60 s, chilled at 2 °C (33% of carcasses); n=2—stimulated for 60 s, chilled at 14 °C (33% of carcasses); n=1—stimulated 15 s, chilled 2 °C (16% of carcasses); n=1—stimulated 15 s, chilled at 14 °C (16% of carcasses)] using the definition of PSE and DFD described in Warner, Kauffman, and Russell (1993).

Results grouped according to rate of pH decline post slaughter

The results for the experiment described in part 1 (Rees et al., in press) and this experiment when grouped according to the rate of pH decline can be seen in Table 5.

The pH at 30 min, 1, 2 and 3 h post slaughter were all influenced by the rate of pH decline (P<0.05 for all) with the fast group having the lowest pH at each time with no differences in pH between the medium and slow groups. At 4, 5 and 6 h post slaughter the fast group had the lowest pH and the pH of the medium group was lower

Discussion

The treatments imposed in this experiment were designed to induce the extremes of protein denaturation and cold shortening. It was hypothesised that by inducing a rapid rate of pH decline with a slow rate of temperature decline, protein denaturation would occur, thus allowing the influence of protein denaturation on the rate of ageing to be determined. To induce variations in the rate of pH decline, electrical and CO₂ stunning was employed as well as a short and long electrical stimulation

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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¹: Present address Food Science and Nutrition, School of Biomolecular and Biomedical Science, Griffith University, Logan Campus Queensland 4111, Australia.

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The influence of the rate of pH decline on the rate of ageing for pork. II: Interaction with chilling temperature

Abstract

Introduction

Section snippets

Methodology

Results

Results grouped according to rate of pH decline post slaughter

Discussion

Acknowledgements

Meat Science

Meat Science

Meat Science

Meat Science

Meat Science

Meat Science

Analytical Biochemistry

Meat Science

Meat Science

Meat Science

Meat Science

Meat Science

Meat Science

Meat Science

Food Quality and Preference

Meat Science

Meat Science

Meat Science

Meat Science

Meat Science

Meat Science

The efficiency of high and low voltage electrical stimulation under different chilling regimes

Canadian Journal of Animal Science

Objective-subjective assessment of meat tenderness

Journal of Texture Studies

Effects of beef carcass electrical stimulation, hot boning and ageing on unfrozen and frozen longissimus dorsi and semimembranosus steaks

Journal of Food Science