M. D. Judge

Bovine muscle shortening and protein degradation after electrical stimulation, excision and chilling☆

Electrical stimulation-dependent improvement in beef tenderness resulted from mechanisms other than avoidance of cold shortening in excised muscle chilled at a normal rate (10°C at 10h post-stimulation). At normal chilling rate, electrical stimulation enhanced degradation of the myofibrillar proteins, alpha actinin and troponin-T, and increased the amount of a 30 000 dalton protein, as assessed by gel electrophoresis, whereas sarcomere lengths were not different from unstimulated muscle. Under slightly accelerated chilling conditions (10°C at 5 h post stimulation), electrical stimulation prevented cold shortening but the meat was more tender than, and had the same sarcomere length as, unstimulated muscle chilled to 10°C in 10 h. Electrical stimulation did not improve the tenderness of beef chilled at a rapid rate (10°C at 2 h post stimulation), nor did it prevent cold shortening when muscles were chilled rapidly.

Antioxidative activity of α-tocopherol in cooked and uncooked ground pork.

The effect of α-tocopherol (0, 100, 200 ppm) on lipid oxidation either in cooked or uncooked ground pork was studied during aerobic storage at 4°C and -20°C. Lipid oxidation was measured using the 2-thiobarbituric acid (TBA) method and rancidity development was scored by a trained sensory panel. Alpha-tocopherol slowed the rate of oxidation in cooked ground pork stored at either 4°C or -20°C and uncooked samples refrigerated for extended periods of time (12 days). In cooked product stored at 4°C where oxidation development was intense and off-flavors were strong, panelists did not detect flavor differences due to treatments. But in cooked product stored at -20°C sensory results were consistent with TBA analysis. Pre-rigor grinding, known to induce a high pH and inhibit lipid oxidation in uncooked fresh pork, had no protective effect on lipid oxidation as measured by TBA values in cooked ground pork, regardless of storage condition. TBA numbers increased during storage of cooked product at 4°C with an increase in internal cooking temperature between 50°C and 80°C. Internal cooking temperatures of 70°C or higher induced a rapid rate of oxidation when stored at 4°C.

Effect of heating rate on shortening, ultrastructure, and fracture behavior of prerigor beef muscle

Rapidly heated prerigor beef is tender because of incompletely described myofibrillar disruption and tissue fracture. This study was designed to evaluate the effects of heating rate on heat-induced myofibrillar shortening, ultrastructural changes, and fracture behavior in prerigor triceps brachii muscle. Rapid heating (2°C/2 min) to 53°C caused (P < 0·05) more severe myofibrillar shortening in a shorter time and at higher muscle pH and temperature, less muscle weight loss, and shorter sarcomeres than slow heating (2°C/12 min) to 47 or 53°C. Rapid heating caused more extensive degradation of A and I bands, greater loss of the tridimensional pattern of myofibrils, more fragmentation and melting of myofibrils, widened intermyofibrillar spaces, and maximum separation of fiber bundles as compared to slow heating. Slow heating caused extensive shortening but not extensive degradation and disruption of myofibrils. Muscles slowly heated to 53°C sustained greater loss of structural integrity than those slowly heated to 47°C, but fracture behavior was similar. Separation and fracture occurred near the perimysial/endomysial junction in all heated samples, but the perimysium remained affixed to the endomysium at one side of the interface in many rapidly heated samples. Longitudinal fractures showed a granular endomysium and large numbers of supercontraction nodes alternating with areas of sarcolemmal membrane fragmentation and fiber tearing in rapidly heated samples. Alterations of myofibrillar ultrastructure and fiber structure, and separation of bundles, may account for enhanced tenderness of rapidly heated prerigor muscle.

Early post-mortem degradation of intramuscular collagen☆

Post-mortem changes in physical and thermal stabilities of bovine intramuscular connective tissue were studied during the first 24 h postmortem. Collagen thermal shrinkage temperature (T(s)) decreased (P < 0·01) and collagen solubility increased (P < 0·01) during the first 24 h following slaughter with greatest amount of change occurring in the first 8 h post mortem. The dynamic nature of intramuscular connective tissue during the very early post-mortem (VEP) period is compared to the VEP-tenderness relationships proposed by Marsh and others.

Extended shelf-life of unrefrigerated prerigor cooked meat

Five experiments were conducted to evaluate the microbial quality of unrefrigerated cooked prerigor beef after the application of oxygen-permeable packaging. Specific objectives were to combine the beneficial effects of aerobic packaging, meat surface acidification and prerigor rapid cooking rates on meat storage stability at ambient temperature. In the experiments, the triceps brachii muscle was dissected from one side 45 min after exanguination of the animal, and samples of 2 × 3 × 5 cm were prepared. Bags made of a strong barrier, plastic film, and a highly oxygen permeable oriented polypropylene, were used. The cooking of the packaged samples covered a number of treatments ranging from cooking in a 70°C water bath to an internal sample temperature of 65°C to cooking in 100°C water for 40 min. Reheating and multiple heat treatments were also included. The pH values of the cooked samples were determined and aerobic plate counts (log(10)/g) were determined for the cooked samples at various intervals during two weeks of storage at 22°C or at 3°C for the control samples. The results indicate that heat treatment alone did not improve shelf stability at 22°C. However, dipping the samples in 80°C solutions of 0·7% citric acid or 1·25% lactic acid for 1 min and draining for 1 min followed by packaging using oxygen permeable bags and cooking in 100°C water for 40 min consistently resulted in shelf stable products at all 22°C storage intervals. The lactic acid treatment was superior to the citric acid treatment because it completely decontaminated the samples and delayed spoilage, especially at 3°C.

Effect of dietary crude protein content on skatole concentration in boar serum

Forty-eight Yorkshire × Chester White crossbred boars, 28 days of age, were assigned to one of four diets differing in crude protein content. Dietary crude protein content was 23% initially and then adjusted to 14, 17, 20 or 23% at 9 weeks of animal age, and 12, 15, 18 or 21% at 14 weeks of age, respectively. The skatole concentrations in serum of the boars was measured at 24, 32 and 40 weeks of age. Results showed that serum skatole concentrations declined (P < 0·05) with increasing age (0·034, 0·027 and 0·021 μg/ml at 24, 32 and 40 weeks, respectively) and also decreased (P < 0·059) with increasing dietary crude protein concentration (0·033, 0·026, 0·022 and 0·021 μg/ml at 12, 15, 18 and 21% in finishing diets, respectively).

Serum skatole detection using gas chromatography and high performance liquid chromatography

Skatole-spiked boar serum was used to evaluate the degradation of skatole during frozen storage and to evaluate gas chromatography (GC) and high performance liquid chromatography (HPLC) for measuring serum skatole. Tubes of serum spiked with 1 ppm skatole which had been stored in a freezer (-15°C) for 4 months and tubes of fresh spiked serum (1 ppm skatole) were utilized. No differences (P > 0·05) between GC and HPLC determination in sensitivity and skatole recovery were observed. Measurements of skatole by GC and HPLC were highly correlated (r = 0·93). Both GC and HPLC revealed no difference (P > 0·05) between fresh spiked serum and stored spiked serum samples.

Shortening and tenderness of pre-rigor heated beef: Part 1 — Effect of heating rate on muscles of youthful and mature carcasses

Pre-rigor cooked beef is tender if the cooking produces severe shortening. This study was conducted to compare the effects of different heating rates on shortening and tenderness. Myofibrillar and cooking shortening and related changes were measured with physiograph recordings on pre-rigor M. triceps brachii strips suspended in paraffin oil during heating. Warner-Bratzler shear values were determined on M. triceps brachii samples heated at approximately the same rates at which the muscle strips were heated. Rapid heating (2°C/2min) produced more (p < 0·01) severe myofibrillar shortening that was complete at higher (p < 0·01) muscle temperatures than slow heating (2°C/12 min). Regardless of animal age, rapid heating resulted in a cooked product that was more (p < 0·01) tender than that produced by slow heating in the pre-rigor state and slow heating resulted in a more (p < 0·01) tender product than that achieved by rapid heating in the post-rigor state. Data on muscle shortening and from differential scanning calorimetry suggest that the tenderness produced from pre-rigor rapid heating results from a heat-induced active contraction.

Effects of early post-mortem ageing on intramuscular collagen stability, yield and composition☆

Post-mortem changes in the composition and physical stability of bovine intramuscular collagen were evaluated during a 24 h ageing period. The yield of intramuscular connective tissue (IMCT) isolated from the infraspinatus muscle samples and the carbohydrate content of that material did not change significantly (P > 0·05) during the ageing period. The collagen content and total protein content of the isolated IMCT increased (P < 0·05) through 8 h post-mortem. Moisture content of the isolated material decreased numerically but not significantly (P > 0·05). Collagen thermal shrinkage temperature (T(s)) decreased (P < 0·01) and collagen solubility increased (P < 0·05) during the ageing period with most of the changes occurring in the first 8 h.

Myofibrillar protein degradation after eccentric exercise

Male rats were run downhill for 90 minutes (nonexhaustive). Following the exercise, muscle protein degradation was increased, as determined by urinary 3-methylhistidine. However, minimal changes were observed in the relative percentage of the minor myofibrillar proteins and in the protease calcium activated factor in the long head of the triceps brachii muscle (eccentrically exercised) following the exercise bout.