Meat texture and flavour always received a great deal of attention from the consumers that seek for high quality eating experience. Other desirable pork meat criterions of importance are namely the juiciness, composition of intramuscular fat, appearance and little drop loss (Andersen and others 2005). Therefore, it is of the pig farmers and pork meat retailers' utmost concern to retain and enhance these eating qualities before presenting the meat to consumers, while considering the financial and technical constraints. The underlying factors that determined eating quality of pork meat include the genotype, breed and age of pig, feeding materials, pre-slaughter conditions, post-slaughter handling, storage conditions and cooking procedures.
It is worthwhile to understand the genetic profile of pig since the growth of lean muscle is generally governed by the porcine stress syndrome gene or best known as halothane gene (Channon and others 2000). In fact, the heterozygote pigs for halothane are more prone to stress before slaughtering. This leads to depletion of glycogen concentration and rapid declination of pH of less than 5.5 which promotes extensive muscle proteins denaturation while the temperature of the carcass is still high (up to 40oC). As a result, the pale, soft and exudative (PSE) pork meat is produced with excessive loss of water and is severely purged. Another gene that confers greater decrement in ultimate pH and water binding capacity (WBC) of pork meat is the rendement napole (RN) gene (Rosenvold and Andersen 2003). Eventually, majority of the pig farmers that suffered economic loss owing to the poor pork quality produced eliminate both the halothane and RN genes at the initial stage of breed selection.
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The feeding materials for the pig have significant impact on the meat tenderness and WBC to a great extent, in terms of altering the rate of muscle growth and the amount of energy available (energy stores of creatine phosphate and glycogen) in muscle upon slaughtering (Anderson and others 2005). The respective work suggested that having high digestible carbohydrate level in the pig's diet prior slaughtering is cost-effective and would increase the glycogen concentration stored in the muscle which is able to delay the onset of rigor mortis. Alternatively, a low protein diet would induce pigs to grow more intramuscular fat within the muscle, which will satisfy the overall eating experience perceived by consumers but the flavour will be slightly reduced (Wood and others 2004). Sadly, the recent effort of Simitzis and the others (2010) to supplement the pig diet with oregano oil to retard the lipid oxidation in order to prevent the development of rancidity in pork meat was reported to have no effect on the eating quality. On the other hand, the wide usage of beta agonist feed additive, such as ractopamine in swine industry, contributes to leaner pork meat and tenderness (Xiong and others 2006). However, this approach draws ethical concerns and hence, not socially acceptable.
Generally, the slaughtering process cuts off the supply of energy and oxygen that ceased the aerobic metabolism of the carcass and glycolysis takes place which depletes the energy currency of adenosine triphosphate (ATP). At this stage, the muscle stiffens as no ATP is available to dissociate the irreversible cross linkages between actin and myosin. This is the onset of rigor mortis which promotes detrimental tough texture to meat, thus the carcass must aged right after slaughter to promote muscle relaxation. The pig carcasses are usually electrically stunned to accelerate the glycolysis and ATP hydrolysis for the muscle enters the rigor state sooner to improve the pork meat tenderness (Devine 2009). Troeger and Benjamin (2003) consider the animal welfare issue by limiting the minimum constant electric current flow of 1.3A for more than 0.3 seconds on the carcass. However, the rapid drop of pH owing to lactic acid accumulation from glycolysis is likely to cause inferior WBC and produce the PSE meat (Rosenvold and Andersen 2003). Conversely, carbon dioxide (CO2) stunning is a more sensible way to improve the meat quality in reducing the incidence of bone fractures and blood splashes that occurred frequently during electrical stimulation.
Both the stunning method of electrical and CO2 are controversial because they introduce merciless physiological stress to pig. Instead, the pelvic suspension is reported by Rosenvold and Andersen (2003) in preventing further muscle shortening effectively. The length of sarcomere prolonged gradually to enhance the meat tenderness and WBC properties. In general, ageing process, ideally up to 10 days under appropriate conditions, is necessary for the muscle proteins to break down in order to tenderise the pork meat and generates flavour upon production of peptides and amino acids (Ngapo and Gariepy 2008). Furthermore, controlling the cooling rate of carcass via strict temperature-time regime, especially four hours after slaughtering or during the transportation to factory for further meat processing or to butchers can avoid the risk of cold shortening that will toughen the meat. Notably, the review paper by Rosenvold and Andersen (2003) reported that the common PSE defects in pork can be minimised through nitrogen chilling, whereas accelerated air chilling showed tendency to control drip loss.
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When retailing the pork meat to the consumers, the modified atmosphere packaging (MAP) of lesser oxygen level under low temperature, is an effective method to reduce the chances of meat lipids rancidity and the muscle proteins oxidation, as well as extending the meat shelf life (Lund and others 2007). As a result, the muscle proteins are less cross links via disulphide bond and the tenderness and juiciness showed significant improvement. After all, MAP is indeed a remarkable development in exporting the pork meat to overseas, while retaining its freshness and bright colour. The meat sensory characteristics of juiciness and tenderness perceived by consumers also depend on the cooking procedure which correlated with the mode of heat transfer, meat surface temperature and the core temperature (Ngapo & Gariepy 2008). In fact, cooking denatures the muscle proteins and forces the water to migrate out from the muscle tissue to evaporate into atmosphere. This resulted pork meat to have weak WBC which exerts considerable impact on juiciness. In comparison, the approach of injecting 5% polyphosphate into pork meat improves the overall juiciness and tenderness of pork meat tremendously. The polyphosphate will raise the meat pH and increase the net negative charges, causing the muscle to swell and improve WBC (Sheard and others 1999).
Although the carcass is handled under strict regime from selecting the best genes in pig to ethical on-farm management prior to slaughtering (such as stress and feed), post-slaughter handling and cooking procedure, the variation of meat quality is yet unexplained. The plausible explanation is that the eating quality perceived by the consumers does not relied on merely one of the factors discussed above, the interaction of more than one factors determines the overall sensory characteristics of meat, i.e. texture and flavour. Many efforts to enhance pork meat quality are undertaken by the pig farmers, as long as the meat is produced at the minimal cost and would still retain the desirable criterions seek by the consumers and have value for money. After all, the potential research opportunity for pork eating quality enhancement in the future to satisfy the changing needs of consumers is to develop fresher approaches to produce pork meat of consistent quality and free from undesirable defects.