Post‐mortem stimulation of carcasses: Effects on biochemistry, biophysics, microbiology, and quality of meat

Effects of medium voltage electrical stimulation on initial pH decline and quality parameters during ageing and frozen storage of Nellore beef

This study aimed to evaluate the influence of medium voltage electrical stimulation (ES) at three different intensities, 200 V (Treatment 200 V, T200), 300 V (Treatment 200 V, T300), and 400 V (Treatment 400 V, T400) on the initial pH decline in post mortem muscle and the quality parameters on M. longissimus thoracis - Nellore beef, both throughout the ageing process and during frozen storage. The colour, cooking loss, and shear force parameters for samples of aged beef were determined. Additional parameters, like thaw loss, pH, and lipid oxidation were also analyzed for the frozen storage. The shear force and cooking loss decreased and colour parameters increased in Nellore beef ES compared with CON on ageing time (14 days). At frozen storage, quality parameters like pH, a*, and b* were reduced over time, and no negative effect on lipid oxidation was found. Electrical stimulation at 200 V demonstrated effectiveness for decreasing shear force to Nellore beef (M. longissimus thoracis) during frozen storage. The application of medium voltage electrical stimulation can contribute to improved quality and tenderness in Nellore beef, both during ageing and frozen storage conditions.

Effects of medium-voltage electrical stimulation on postmortem changes in fat-tailed sheep

Effects of different medium-voltage electrical stimulation (ES) and ageing on postmortem changes in longissimus dorsi muscle of the fat-tailed sheep were studied. Fifteen male animals were divided into 5 equal groups (n= 3) including: T₁ (control, without ES), T₂ (100 V/30 s), T₃ (100 V/60 s), T₄ (150 V/30 s), and T₅ (150 V/60 s) with fixed frequency of 50 Hz. Five minutes after sticking, the carcasses were stimulated in order of the treatments. After normal processing, they were kept at 6 °C for 14 d. ES accelerated the glycolytic rate resulting in a significant fast fall in pH (P < 0.05) during the 1st 6-h postmortem (PM) with a gradual decline until 24-h PM, and a simultaneous significant reduction in adenosine triphosphate (ATP) content (P < 0.05). There was a significant (P < 0.05) decline in the total calpain activity during the 1st 6-h PM. The muscles from ES carcasses had significantly (P < 0.05) lower water holding capacity (WHC) than those from nonstimulated ones. Ageing revealed a significant (P < 0.05) effect on the reduction of WHC. No significant difference was found for the mean value of the muscle color (L*, a*, and b*) in all treatment groups during ageing (P > 0.05). The results of free amino acid (FAA) content and myofibrillar fragmentation index (MFI) revealed a significant improvement of proteolysis and tenderness by ES and ageing (P < 0.05). In the present study, higher voltage/duration (150 V/60 s) showed greater effects and significantly accelerated glycolysis, pH decline, and ATP depletion and thus decreased the time for rigor completion and improved the tenderness.

Case studies demonstrating the benefits on pH and temperature decline of optimising medium-voltage electrical stimulation of lamb carcasses

The efficacies of electrical stimulation practices at Australian abattoirs that process significant proportions of Australian lamb and sheep meat were assessed. Several abattoirs used medium-voltage electrical stimulation system (MVS) units suboptimally and many carcasses at these abattoirs exhibited a poor rate of pH decline and, consequently, a low proportion of carcasses attained pH 6 at a carcass temperature of 18−35°C, according to Sheep Meat Eating Quality pH–temperature guidelines as adopted by Meat Standards Australia. In the present communication, we describe the causes of suboptimal results with electrical stimulation and discuss procedures for optimising the stimulation dose delivered by MVS units. Carcass pH responses to various levels of current and pulse width were assessed to determine the best MVS settings for individual abattoirs. The MVS units at the abattoirs involved in the present study have now been programmed for optimal efficacy and carcass quality will be monitored on an ongoing basis. Evaluation of methods for assessing the proportion of carcasses that fall within the optimum pH–temperature window showed that a random regression model is more accurate than the current approach.

Effect of some electrical stimulation variables on wing flapping, post-mortem glycolysis and eating quality characteristics of broiler pectoralis major muscle

1. The influence of different rates of wing flapping on the rate of post-mortem glycolysis in the Pectoralis major (PMI) muscles of commercially-processed broilers was investigated. This was achieved by applying 300 pulses of low voltage electrical stimulation (ES) shortly after slaughter at various frequencies and pulse widths. The rate of post-mortem glycolysis was assessed by measuring muscle pH values at 20 min post mortem (pH(20 min)). 2. ES gave a mean pH(20 min) value of 6.01, significantly lower than that of the control carcases which had a mean value of 6.45. Within ES treatments, variation in pulse frequency between 1/s and 10/s and in pulse width from 5 to 20 ms had no influence on pH(20 min) values as measured by direct probe. However, differences between mean pH(20 min) values attributable to pulse frequency were detected when measured by the iodoacetate method. 3. A further experiment was carried out to determine how different rates of wing flapping would affect the eating quality of PM muscles from commercially-processed broilers stored at chill temperatures for 24 h post mortem. This was achieved by using pulse frequencies of 1/s, 5/s and 10/s, all other ES variables being standardised. Pulse frequency had no effect on ultimate pH, sarcomere length, cooking loss or tenderness of PM muscle compared to controls. 4. We concluded that the rate of wing flapping post-slaughter has no effect, per se, on the extent of post-mortem glycolysis in broiler PM muscle or on its subsequent meat quality assessed after holding the carcases under chill storage conditions for 24 h.

Effects of electrical stimulation on the post-mortem biochemical changes and texture of broiler pectoralis muscle

A study was conducted to determine the influence of electrical stimulation (50,200, or 350 V ac) on biochemical and textural changes in broiler breast muscle. Sixty-four broilers were stunned (50 V ac) prior to kill, and all but a control group were pulse stimulated during bleeding. After processing, carcasses were held in 10-C water for 1 h, then in 2-C ice/water slush for 1 h prior to muscle removal at 2 h post-mortem (PM). Bagged samples were held at 2 C for 24 h, then cooked. The pH, R value (ratio of adenine nucleotides to inosine nucleotides), cook yield, fluids and solids lost (F&S), and objective texture were measured. In addition, 16 broilers processed in the same manner were used in producing a profile of sarcoplasmic protein/enzyme changes in the breast muscle by cation exchange fast protein-liquid chromatography at 10 min, 2, and 24 h PM. The R values and soluble protein were also determined. Stimulation at 200 and 350 V accelerated the onset of rigor noted by lower pH values at 10 min and 1 h PM, and higher R values at 2 h PM. Muscle stimulated at 350 V exhibited the lowest cook yield and highest percentage of F&S lost, suggesting both the loss of functional properties and muscle integrity due to this treatment. All control and stimulated samples exhibited shear values in excess of what would be considered tender. Hardness and chewiness values increased as stimulation voltage levels increased. Only one of the seven principal chromatographic peaks decreased in response to increased electrical stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Functionality of muscle proteins in gelation mechanisms of structured meat products

Recent advances in muscle biology concerning the discoveries of a large variety of proteins have been described in this review. The existence of polymorphism in several muscle proteins is now well established. Various isoforms of myosin not only account for the difference in physiological functions and biochemical activity of different fiber types or muscles, but also seem to differ in functional properties in food systems. The functionality of various muscle proteins, especially myosin and actin in the gelation process in modal systems which simulate structured meat products, is discussed at length. Besides, the role of different subunits and subfragments of myosin molecule in the gelation mechanism, and the various factors affecting heat-induced gelation of actomyosin in modal systems are also highlighted. Finally, the areas which need further investigation in this discipline have been suggested.