Electrical stimulation of rats: Part 2-The effect of electrical parameters on muscle tension and post-Mortem glycolysis.

Anaesthetized rats were used as a model to determine the effect of changes in electrical stimulation parameters on the pH fall of the M. longissimus dorsi and M. triceps surae and tension development by the M.

Structural changes developing with rigor that facilitate bacterial invasion of muscle tissue.

Pre-rigor skeletal muscle fibres shrank in hypertonic and swelled in hypotonic fixative solutions, but the radial dimensions of post-rigor muscle fibres did not change with variations in the effective osmolalities of fixative solutions. Muscle fibres apparently undergo radial shrinkage during the development of rigor and, in so doing, can pull away from their surrounding endomysia. The resulting gaps between post-rigor muscle fibres and endomysia probably contain muscle cell cytoplasm.

'Ageing' of cold shortened meat depends on the criterion.

Although cold shortened muscles show little decline in shear force during ageing, they do, like unshortened muscles, undergo a drastic reduction in yield point. The differing responses to the two criteria arise from the involvement of different structural elements. Our previous claim, that yield point is highly sensitive to ageing and reflects changes in tenderness, remains valid for unshortened muscles, but is clearly inappropriate to cold shortened samples.

Tenderisation of meat by pressure-heat involves weakening of the gap filaments in the myofibril.

These results confirm previous Australian experience that pressure-heat (P-H) treatment tenderises rigor meat effectively only after considerable periods at elevated temperatures; that prior ageing abolishes the effect; and that cold shortened meat is effectively tenderised. Yield point is also profoundly affected by P-H, although this effect is not related to tenderness. As predicted by the new G-filament theory of meat tenderness, P-H greatly weakens the G-filaments.

Meat Spoilage and Evaluation of the Potential Storage Life of Fresh Meat.

Microbiological processes by which meat develops qualities unacceptable to consumers vary with the composition of the meat and spoilage microflora. Composition of the spoilage microflora is affected by meat composition and storage conditions. Aerobic spoilage microfloras are usually dominated by pseudomonads.

Electrical stunning of lambs: The effect of stunning parameters and drugs affecting blood flow and behaviour on petechial haemorrhage incidence.

Head-to-back electrical stunning of lambs results in speckle bruising, a kind of petechial haemorrhage in muscle fascia, especially when the lamb is tightly restrained. Other factors still appear to modify speckle and some of these are investigated here. There was a significant increase in leg speckle with long stunning duration or high stunning current, but there was little or no increase for the loin.

Effect of electrical stunning methods on petechial haemorrhages and on the blood pressure of lambs.

Electrical stunning of lambs to render them unconscious and insensible to pain can result in blood splash (spots of blood in muscles) or speckle (petechial haemorrhages in fat or connective tissue overlying the muscle). Stunning through electrodes applied to the head causes mainly blood splash with some speckle, while currents applied head-to-back or head-to-foreleg can produce speckle without blood splash. To identify the causes of speckle, animal movement and blood pressure changes that occur during stunning were measured.

Myofibrils of cooked meat are a continuum of gap filaments.

When cooked meat is subjected to high degrees of stretch it becomes apparent in high magnification electron micrographs that A-filaments have ceased to exist. The A-band is filled with a coagulum of actomyosin. Fragmentation of this coagulum during stretch reveals an array of fine filaments (identified as gap filaments).

The occurrence of Clostridium botulinum at aquatic sites in and around Auckland and other urban areas of the North Island.

Samples of bottom muds from lakes and waterways in the Auckland area were inoculated into bottles of cooked meat medium. After incubation, the media were tested for production of Clostridium botulinum toxin which was detected with samples from 11 of the 20 sites examined. Although toxins produced from all positive samples were neutralized by specific antisera of both type C and D toxins, it is likely that C.

Physiological basis of CO(2) inhibition of a meat spoilage bacterium, Pseudomonas fluorescens.

CO(2) has been shown to have a number of effects on biological systems, but it is uncertain which of these are important in its inhibition of Gram-negative spoilage bacteria. The effects of CO(2) on intracellular pH, in vitro enzyme actities and substrate transport were examined to see if any changes in these functions could be correlated with the observed patterns of growth inhibition, which varied with the composition of the growth medium. CO(2) inhibition of growth could not be explained by postulating inhibition of intracellular enzymes, but inhibition of substrate uptake appears to correlate with-and offer a satisfactory explanation for-growth inhibition.

Microbiological and Organoleptic Qualities of Bruised Meat.

Naturally bruised tissues from the carcasses of cattle and sheep slaughtered and processed at a commercial abattoir were compared with unbruised tissues from similar areas of the same carcasses. There were no microbiological differences between the two types of tissue when bruised tissues were subject to the same conditions as unbruised tissue during processing of carcasses. Bruised tissue had a slightly higher water content and imparted a salty taste to minces prepared from it.

Osmotic properties of post-rigor beef muscle.

The osmotic pressure of beef sternomandibularis and psoas muscles ranged from 480 to 540 mOs, which is almost twice that of pre-rigor muscle (about 300 mOs). The post-rigor osmotic pressure appears to be satisfactorily explained by the low molecular weight components. Muscle samples were soaked at 2°C for 24 h in various solutions and sample weight changes were recorded.

Residual blood in lamb muscles.

The effect of slaughter method on the residual blood content of the M. longissimus dorsi, the microbiological status of the meat and its tenderness was examined with lambs. There were no differences in any of the characteristics examined between the various stunning procedures used, even though there were marked differences in the amount of blood collected after slaughter.

The microbiology of DFD fresh meats: A review.

Muscle which is deficient in glycogen because of exercise or stress prior to slaughter produces dark, firm, dry (DFD) meat. Such meat is characterized by a high ultimate pH (>6·0) and deficiencies in glucose and glycolytic intermediates. These factors can result in bacterial spoilage becoming evident at an early stage of growth of the meat flora.

Evaluation of the total carbonaceous biochemical oxygen demand method, using a compensated recording respirometer.

The total carbonaceous biochemical oxygen demand test is described, and experimental data demonstrating its stoichiometry, precision, and accuracy are presented. The test is more reproducible and faster than the current 5-day biochemical oxygen demand test procedure, and if a respirometer is used, the effects of toxic chemicals, pH changes, and nutrient imbalances can be routinely monitored. The design principles of a multichannel compensated recording respirometer suitable for this test are described.

Post-mortem changes in cytoskeletal proteins of muscle.

Progressive changes have been identified in the solubility of muscle-cell proteins during post-mortem muscle ageing, particularly the cytoskeletal proteins, desmin and connectin. Ox sternomandibularis muscle was sampled immediately post mortem and up to six days later. It was homogenised and separated into three salt-soluble fractions: phosphate soluble, concentrated KI soluble and guanidine-HCl soluble.

Rapid freezing, frozen storage and the tenderness of lamb.

Cold-shortening in pre-rigor lamb can be prevented by freezing carcasses very rapidly in less than four hours. Thaw-shortening can also be prevented by storing the carcasses for a period (> 10 days) in the frozen state (- 12°C). By this simple combination of rapid freezing and frozen storage, the hazard of toughness development from cold- and thaw-shortenings is avoided.

Effect of Electrical Stimulation on Meat Spoilage Floras.

Sheep carcasses were electrically stimulated after removal of one leg. There was no difference between the growth of spoilage bacteria on stimulated and non-stimulated legs, or in minces prepared from either type of leg, with either the natural or an inoculated flora.

Studies in electrical stimulation: Post-mortem decline in nervous response in lambs.

A study has been made of the effects of electrical stimulation, either indirectly through the nerves or directly through the muscles, on glycolysis in lamb hind leg muscles. Responses were affected by delay before application and the stimulating voltage. At 5 min post mortem the same fall in pH during stimulation (ΔpH) and subsequent increased rate of pH fall (dp H/dt) occurred in muscles stimulated both directly and indirectly with 12 V.

The ecology of bacterial spoilage of fresh meat at chill temperatures.

At chill temperatures the spoilage flora of meat is composed of psychrotrophs originating largely from the hides of slaughtered animals. Under humid conditions, aerobic floras are usually dominated by pseudomonads while anaerobic floras are dominated by lactobacilli. In both cases growth occurs on low molecular weight soluble components of meat which are attacked in the order glucose, glucose-6-phosphate (Enterobacteriaceae only) and amino acids.

Electrical stimulation, muscle tension and glycolysis in bovine Sternomandibularis.

Electrical parameters previously employed to hasten the onset of rigor mortis in carcasses were derived empirically. Various parameters have been studied to determine their relationship to the two-stage fall of muscle pH resulting from stimulation. At any given stimulation period pulse frequency had a considerable effect on the magnitude of the pH fall that occurs during stimulation, the greatest falls, ∼ 0·7 pH units in a 120 sec period, being achieved with 5 to 16·6 pulses.

Cooking tenderizing in beef.

Heating tenderzes meat in three distinct phases. Up to 65°C aging occurs through proteolysis at specific sites in the myofibrils. From about 70°C the collagen of the connective tissue is denatured and melts.

The histology of blood splash in lamb.

Ecchymosis (blood splash), can occur in the carcasses of animals that have been stunned electrically or shot with a captive bolt. While blood splash presents no health hazard, it is likely to detract from the acceptable appearance of the meat. Based on light and electron microscopic studies, ecchymosis has been shown to be due to the localised discharge of blood from ruptured blood vessels into the surrounding muscle tissue.