The influence of the rate of pH decline on the rate of ageing for pork. I: interaction with method of suspension.

The influence of the rate of pH decline post slaughter on the rate of ageing of pork 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). To investigate the effect of pH decline rate on ageing rate independently of the effect on possible muscle shortening, sides were suspended by either the pelvis (to minimize shortening) or conventionally by the Achilles tendon. The data indicated that the rate of pH decline did not influence the rate of ageing but the use of LVES did improve tenderness at 1, 2 and 10 days post slaughter due to the prevention of muscle shortening. Electrical stunning improved tenderness at 1 and 2 days post-slaughter but had a detrimental effect on drip loss. Pelvic suspension improved tenderness at rigor, 1, 2 and 6 days post slaughter due to prevention of muscle shortening. The conditions employed however were not severe enough to induce protein denaturation.

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

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.

Temperature and pH dependence of the autoxidation rate of bovine, ovine, porcine, and cervine oxymyoglobin isolated from three different muscles--Longissimus dorsi, Gluteus medius, and Biceps femoris.

This study examined the temperature and pH dependence of the in vitro autoxidation rate of bovine, ovine, porcine, and cervine oxymyoglobin that had been isolated and purified from three muscles of different oxidative stability--Longissimus dorsi, Gluteus medius, and Biceps femoris. To avoid obtaining unreliable estimates of autoxidation rate as has occurred in many previous studies, in this study, precautions were taken to eliminate the effects of freezing, chemical reduction with hydrosulfite, and contaminating metal ions on the reaction rate. When these precautions were taken, the rate constants for the different myoglobins studied were similar to each other but were 2-7-fold lower, and the Ea (activation energy) was 20-100% higher than that reported in most previous studies. The type of muscle the myoglobin was isolated from had no effect on the reaction rate or the Ea; however, the species did have a significant effect (p < 0.05) with porcine myoglobin having a 10% lower reaction rate and a 20% lower Ea than myoglobin from the other species. Increasing the reaction pH from 5.50 to 6.50 produced an exponential increase in reaction rate but only a small curvilinear change in Ea that had a maximum at pH 6.00.

Effect of tocopherol concentration on rancidity development during frozen storage of a cured and an uncured processed pork product.

This research evaluated the effect of addition during processing of various concentrations of tocopherol (0-1000 mg/kg) on the subsequent lipid oxidation and rancidity development during frozen storage of two pork products-a coarsely ground cured sausage and an uncured restructured pork roast. The results indicated that tocopherol had little effect on lipid oxidation, as measured by TBARS values and sensory evaluation during frozen storage at -18 °C for 37 weeks for either product. However, lipid oxidation only occurred to a limited extent even in products without tocopherol and was insufficient to cause rancid flavour development. It was, therefore, not possible to determine if tocopherol added during processing was effective as an antioxidant in preventing lipid oxidation in processed pork products during frozen storage.

Effect of dietary vitamin E, fishmeal and wood and liquid smoke on the oxidative stability of bacon during 16 weeks' frozen storage.

Twelve (Large White×Landrace) gilts were randomly allotted in a 2×2 factorial design with the respective factor being dietary vitamin E (10 or 200 mg/kg feed) and dietary fishmeal (0 or 5%). Bacon was manufactured from the meat obtained from the animals after slaughter using wood smoke only or a combination of liquid and wood smoke. The oxidative stability of the bacon was examined over 16 weeks of frozen storage. Lipid oxidation in the product was measured by means of thiobarbituric acid reactive substances (TBARS) and fluorescence shift. Dietary fishmeal supplementation increased lipid oxidation in bacon, while dietary vitamin E supplementation reduced lipid oxidation in the product. Lipid oxidation in frozen bacon was successfully reduced when bacon was manufactured from pigs fed a diet supplemented with or without 200 mg of α-tocopherol per kilogram of feed and processed with a combination of liquid and wood smoke. It is concluded that bacon processed with a combination of liquid and wood smoke was significantly less (P<0.001) susceptible to lipid oxidation than bacon processed with wood smoke only.

Antioxidant effects of rosemary extract and whey powder on the oxidative stability of wiener sausages during 10 months frozen storage.

Twelve (Large White×Landrace) gilts were randomly allotted in a 2×2 factorial design with the respective factors being dietary vitamin E (10 or 200 mg/kg feed) and dietary fishmeal (0 or 5%). Wiener sausages were manufactured with or without antioxidants such as rosemary extract and sweet whey powder from meat obtained from the animals after slaughter and stored for 5 days at 4 °C. The oxidative stability of the wieners was examined over ten months of frozen storage. Lipid oxidation in the product was measured by means of thiobarbituric acid reactive substances (TBARS) and fluorescence shift. Sensory evaluation of the product to detect oxidative changes was also carried out. The fluorescence shift method was unsatisfactory in the case of wieners containing rosemary extract, as it appeared that the extract contained compounds that fluoresced and therefore interfered with the method. No lipid oxidation as measured by TBARS, fluorescence shift and sensory analysis was observed in wieners stored at -20 °C for 10 months. The oxidative stability of wieners was unaffected (P>0.05) by dietary treatments or by the addition of antioxidants. The high oxidative stability of the wieners, even in the absence of antioxidants, could be due to sodium erythorbate present in the formulation as an additional antioxidant.

Tenderness, ageing rate and meat quality of pork M. longissimus thoracis et lumborum after accelerated boning.

The impact of accelerated boning on tenderness, ageing rate and meat quality of pork longissimus muscle was investigated. Accelerated boning of eight Large White×Landrace pork carcasses at 30 min post-mortem followed by chilling at 0°C resulted in tougher pork with higher drip loss and a darker surface lightness relative to conventional boning at 24 h post-mortem. The increased toughness was still observed at 4 days post-mortem, a time by which 80% of ageing generally had occurred as seen in experiment 2. The increased toughness could be attributed to cold shortening and a reduction in proteolysis.

Effect of calcium infusion on tenderness and ageing rate of pork m. longissimus thoracis et lumborum after accelerated boning.

The effect of calcium chloride infusion at either 0.5 or 6 h post slaughter on tenderness, ageing rate and meat quality of pork longissimus muscle that had been boned at rigor or had undergone accelerated processing and conditioning at either 0 °C or 14 °C was investigated. The time of calcium infusion had no effect on the initial WBSF values or the aging rate. However, calcium infusion overall resulted in lower WBSF initially (1-day post-mortem) and also after 6 days ageing at 2 °C regardless of the processing procedures used. Calcium infusion did not, however, increase the ageing rate compared to comparable treatments that had not been calcium infused. Based on this observation and the myofibrillar fragmentation index results, it was concluded that the increased tenderness due to calcium infusion was not due to increased proteolysis as has been previously postulated, but was due to either a direct effect of calcium on tenderness, or an indirect effect of calcium via increased post-mortem glycolysis and pH decline rate resulting in reduced cold shortening. Calcium infusion had detrimental effects on drip loss and meat colour.

Tenderness of pork m. longissimus thoracis et lumborum after accelerated boning. Part I. Effect of temperature conditioning.

This research investigated the effect on tenderness and meat quality of temperature conditioning at 0, 7, 14 or 21 °C of pork longissimus muscle after accelerated boning (removal from the carcass within 30 min post slaughter). The conditioning temperature had no effect (P>0.05) on tenderness at the end of the conditioning period (i.e. at the onset of rigor) but had a significant effect (P<0.05) after the muscles were aged for four days at 2 °C. After aging, the muscles conditioned at 14 °C were more tender than muscles conditioned at the other three temperatures; the muscles conditioned at 0 °C were tougher than the muscles conditioned at the higher three temperatures. Conditioning at 14 °C produced muscles that had lighter surface colour and lower drip loss due to prevention of cold toughening which occurred at lower temperatures or protein denaturation at the higher temperatures.

Tenderness of pork m. longissimus thoracis et lumborum after accelerated boning. Part II. Effect of post-slaughter ageing.

This research investigated the effect of ageing time (0-10 days) at 2 °C on tenderness of pork longissimus muscle after either rigor boning (RB) or accelerated boning (removal from carcass within 30 min post slaughter) and temperature conditioning at either 0 or 14 °C. Ageing occurred most rapidly in muscles conditioned at 14 °C- maximum tenderization occurred by 4 days post-mortem. RB muscles and muscles conditioned at 0 °C aged more slowly and took 8 and 10 days, respectively, to reach a comparable level of tenderness. Temperature conditioning at 14 °C, produced muscles which had lower drip loss and lighter surface colour.