Biochemical and structural changes in carcass and meat during the first 24 hour post mortem

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INTRODUCTION

In recent times, there has been a substantial increase in the live and carcass weight of cattle, especially feedlot cattle that are slaughtered in South Africa and many other parts of the world. Carcass weights have increased on average of 1 to 2 kg each year in recent time in USA (Savell, 2012). This is according to the findings of the National Beef Quality Audit (Lorenzen et al., 1993; Moore et al., 2012). In Australia, average slaughter weight increased from 180 kg in 1983/84 to 232 kg in 2003/2004 (Department of Agriculture, Fisheries and Forestry, 2005) and to 287 kg in 2011 (Meat and Livestock Australia (MLA)). In Finland, the average carcass weight of slaughtered bulls increased from 275 kg (1996) to 335 kg (2008) over twelve years (Pesonen et al., 2012). Currently in Finland, bulls are slaughtered at an average carcass weight of 400 kg (Pesonen et al., 2012).
The increase in carcass weight in South Africa is due to a number of factors, including higher grain prices, because of the current drought and economic downturn. This compels feedlot farmers to feed their cattle for longer, to attain higher live weight, and to cover the cost on the higher priced grains. Other factors include better management practices such as genetic improvement, improved nutrition and the use of feed additives and growth regulating molecules including hormonal implants and beta-agonists. According to Ellies-Oury et al. (2017), the link between carcass weight and meat quality has produced various results depending on experimental conditions such as production systems, breed and animal type. One such beta-agonist that is approved and commonly used in South Africa is zilpaterol hydrochloride (Zilmax®). Delmore et al. (2010) reported about 10 to15 kg increase in live and carcass weights, respectively, when cattle were fed with Zilmax, while Strydom et al. (2009) reported about 14 kg increase in carcass weight. Heavier carcasses favour slaughter house pricing in many countries, including South Africa (Pesonen et al., 2012). Also, the production of heavier carcasses through better nutritional interventions, and the use of feed additives and improved genetic selection, has the potential to produce more beef with fewer cattle which implies lower waste, and less use of land, water and energy. However, little research has been done to compare meat qualities from heavy and lighter carcasses. On the other hand, the increase in carcass weight presents challenges to the processors, in that, these heavier carcasses have to be processed with the same systems and facilities that were designed for lighter carcasses, decades ago. There are also reports that these heavier carcasses require less ES to achieve a similar glycolytic rate than lighter carcasses (Thompson 2002).
According to Hopkins et al. (2007b) and Warner et al. (2014a), most of the heavier carcasses in their experiments exhibited faster pH decline and did not meet the MSA (Meat Standard Australia) pH/temperature window, compared with lighter carcasses. The phenomenon of faster pH decline at high carcass temperature (i.e. pH6 at temperature above 35 OC –Thomson, 2002), especially in heavier carcasses, has recently become the subject of interest and investigation. In a study across the beef industry in Australia, 72% of the carcasses exhibited high rigor temperature which occurred mostly in the heavier carcasses from feedlot (Warner et al., 2014). This was attributed to higher blood plasma insulin resistance, increased electrical inputs and increased number of days on feed. DiGiacomo et al. (2014) indicated that high energy feed such as in feedlot, results in heavier cattle and increased fat level which subsequently reduces carcass cooling. Warner et al. (2014a) reported that insulin resistance could lead to decreased heat tolerance and, as a result, increased carcass temperature at slaughter. An important intervention in reducing the problems of variability in meat quality is the use of electrical stimulation (ES) (Hopkins & Toohey, 2006), which has now been adopted by most commercial slaughter house in many countries including South Africa. Electrical stimulation was adopted initially to accelerate post-mortem (pm) glycolysis, so that rapid cooling can take place, without the risk of cold shortening (Davey & Chrystall, 1980). It was later discovered that ES played a huge role in meat tenderization and colour enhancement and has since been adopted as a method of meat tenderization and colour enhancement in beef, lamb, and goat carcasses (Geeesink, van Laak, Banier, & Smulders, 1994; Savell, Smith, Dutson, Carpenter, & Sutter, 1977; McKeith et al., 1981).
Electrical stimulation has been adopted as a processing procedure by commercial meat processors in South Africa. Low voltage electrical stimulation (LVES) has been described by a number of authors as more practical, more attractive, cheaper and easy to install. It therefore attracts less stringent rules in terms of safety and occupational health harzards from government regulating agencies compared with high voltage equipment (Fabianson & Reutersward, 1985; Hawrysh, Shand, Wolfe, & Price, 1987). LVES has also been reported to achieve similar muscle glycolytic response and meat quality traits to high voltage electrical stimulation (HVES) (Aalhus, Jones, Lutz, Best, & Robertson, 1994; Taylor & Marshall, 1980). According to Bouton et al. (1978), LVES (110 V) lowered muscle pH effectively and improved meat tenderness. This was one of the reasons that 110 V electrical stimulator was used in this trial. However, some authors reported negative results on the effectiveness of LVES on meat quality (Unruh, Kastner, Kropf, Dikeman, & Hunt, 1986) while some some reported little or no effects (Rodbotten, Lea, & Hildrum, 2001), others reported deleterious effects (Hector et al., 1992; Simmons et al., 2008). Timing and duration of application of LVES are important factors to be considered in relation to meat quality.
Chrystall et al. (1980) suggested that for LVES to be effective, it must be applied within a short time of slaughter. On the contrary, Hwang and Thompson (2001b) reported that early stimulation (3 min pm) is detrimental to meat tenderness compared with late application (40 min pm) irrespective of the type of stimulation (LVES or HVES). The authors emphasized that timing and type of stimulation would affect pH decline, enzyme activity and hence shear force of meat. The duration of stimulation is equally important. Roeber et al. (2000) reported that duration of ES and voltage intensity affected beef colour and tenderness. Gursansky, O’Halloran, Egan and Devine (2010) stated that HVES delivered satisfactory results in all circumstances but low voltage could be equally advantageous as long as the duration was not too short (> 40 s as opposed to 10 s). Strydom and Frylinck (2014) also concluded that shorter duration of stimulation (15 s, compared with 45 or 90 s) is more beneficial to water holding capacity and tenderness, where pre-slaughter stress is minimized.

CONTENT :

• LIST OF TABLES
• LIST OF FIGURES
• LIST OF ABBREVIATIONS
• DEDICATION
• ACKNOWLEDGEMENTS
• DECLARATION
• ABSTRACT
• SUMMARY OF RESULTS
• CHAPTER
  • INTRODUCTION
• • 2.1 Biochemical and structural changes in carcass and meat during the first 24 hour post
  • mortem
    • 2.1.1 pH decline
    • 2.1.2 Rigor mortis
    • 2.1.3 Cold and heat shortening or toughening
  • 2.2 Trends and effects of carcass weight increase on carcass and meat quality
  • 2.3 Electrical stimulation, types of electrical stimulation and their merits and demerits
    • 2.3.1 Low voltage electrical stimulation
    • 2.3.2 High voltage electrical stimulation
  • 2.4 Time of application of electrical stimulation on carcasses and its effect on meat quality
  • 2.5 Durations of electrical stimulation and their effects on carcass and meat quality
  • 2.6 Effects of carcass weight on the efficacy of electrical stimulation and the resultant carcass and meat quality attributes
  • 2.7 Effects of electrical stimulation on some carcass and meat quality attributes
    • 2.7.1 Effects of electrical stimulation on pH/temperature decline
    • 2.7.2 Effects of electrical stimulation on meat shear force
    • 2.7.3 Effects of electrical stimulation on meat water holding capacity
    • 2.7.4 Effects of electrical stimulation on sarcomere length
    • 2.7.5 Effects of electrical stimulation on myofibrillar length
    • 2.7.6 Effects of electrical stimulation on meat colour attributes
    • 2.7.7 Effects of electrical stimulation on muscles and energy metabolites: lactate, glucose, glycogen, creatine phosphate, adenosine-tri-phosphate, & glucose-6-phosphate
  • 2.8 Post-mortem proteolysis and proteolytic systems
    • 2.8.1 The calpain system
    • 2.8.2 Calpastatin and its role in meat toughness
    • 2.8.3 Effect of carcass weight and high rigor temperature on proteolytic activity
  • 2.9 Zilpaterol hydrochloride and its effects on carcass and meat quality
• CHAPTER MATERIALS AND METHODS
  • 3.1 Location of the trial and environmental conditions
  • 3.2 Experimental animals
  • 3.3 Slaughter process
  • 3.4 Slaughter schedule and post-slaughter processes
    • 3.4.1 Slaughter schedule and treatments
    • 3.4.2 Electrical stimulation and sampling
  • 3.5 Methods
    • 3.5.1 pH and temperature measurement
    • 3.5.2 Subcutaneous fat measurement
    • 3.5.3 Percentage cooking loss
    • 3.5.4 Meat shear force
    • 3.5.5 Drip loss
    • 3.5.6 Water holding capacity
    • 3.5.7 Sarcomere length
    • 3.5.8 Myofibril fragment length
    • 3.5.9 Meat colour
    • 3.5.10 Energy metabolites determination (μmol/g)
    • 3.5.11 Proteolytic enzymes determination
  • 3.6 Statistical analysis
• CHAPTER RESULTS
  • 4.1 pH
  • 4.2 Temperature
  • 4.3 pH and temperature relationship
  • 4.4 Subcutaneous fat
  • 4.5 Shear force
  • 4.6 Cooking loss
  • 4.7 Drip loss
  • 4.8 Water Holding Capacity
  • 4.9 Sarcomere length
  • 4.10 Myofibril fragment length
  • 4.11 Meat Colour- Lightness
  • 4.12 Meat Redness
  • 4.13 Meat yellowness
  • 4.14 Meat Chroma
  • 4.15 Hue angle
  • 4.16 Energy metabolites
    • 4.16.1 Lactate
    • 4.16.2 Glucose
    • 4.16.3 Glycogen
    • 4.16.4 Creatine phosphate
    • 4.16.5 Adenosine tri-phosphate
    • 4.16.6 Glucose-6-phosphate
    • 4.16.7 Glycolytic potential
  • 4.17 Proteolytic enzymes
    • 4.17.1 Micro calpain (calpain-1)
    • 4.17.2 M calpain (Calpain-2)
    • 4.17.3 Calpastatin
    • 4.17.4 Calpastatin to calpain-1 ratio
    • 4.17.5 Ratio of calpastatin to calpain-1 plus calpain
  • 4.18 Important correlations
  • 4.19 Regressions
• CHAPTER DISCUSSION
  • 5.1 Muscle pH and its decline
  • 5.2 Carcass temperature and its decline due to treatments
  • 5.3 pH and temperature interactions
  • 5.4 Subcutaneous fat (mm)
  • 5.5 Effects of treatments on meat shear force
  • 5.6 Cooking loss
  • 5.7 Drip loss
  • 5.8 Water holding capacity
  • 5.9 Effects of treatments on sarcomere length
  • 5.10 Effects of treatments on myofibril fragment length
  • 5.11 Effects of treatments on Meat Lightness
  • 5.13 Effects of treatments on meat yellowness
  • 5.14 Effects of treatments on chroma
  • 5.15 Effects of treatments on hue angle
  • 5.16 Effects of treatments on energy metabolites
    • 5.16.1 Lactate
    • 5.16.2 Glucose
    • 5.16.3 Glycogen
    • 5.16.4 Creatine phosphate
    • 5.16.5 Adenosine tri-phosphate
    • 5.16.6 Glucose-6-phosphate
    • 5.16.7 Glycolytic potential
  • 5.17. Effects of treatments on proteolytic enzymes
    • 5.17.1 Calpain
    • 5.17.2 Calpain
    • 5.17.3 Calpastatin
  • CONCLUSIONS AND RECOMMENDATIONS
  • BIBLIOGRAPHY

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