Effects of electrical stimulation and temperature on beef quality and tenderness

Beef carcasses were stimulated with either 50 or 500 V and exposed to three chilling temperatures during the first 3 to 9 h post mortem. Both high (HV) and low voltage (LV) electrical stimulation (ES) treatments improved lean maturity scores, lowered the pH values at 2 h through 12 h and reduced the time required for the ATP level to reach minimum values. Both HV-ES and LV-ES treatments influenced firmness, fragmentation and connective tissue (CT) residue as measured by sensory panel and reduced Instron shear value (ISV) of loin steaks. The 30°C temperature treatment had an adverse effect while the 20°C temperature treatment had a beneficial effect on ISV and panel ratings for firmness and CT residue. There was an interaction between conditioning treatments and ES for ISV and sensory panel traits. The LV-ES-20C treatment resulted in the lowest ISV and superior panel ratings; however, the LV-ES-30C treatment had ISV and sensory panel ratings that were similar to the NES-2C (control) group.     

Post-mortem electrical stimulation and high temperature ageing of hot-deboned beef

The effects of electrical stimulation (80-100 V, 15 pps) of hot-deboned, bovine Longissimus dorsi muscles, followed by ageing at 30° or 40°Cfor 5, 7 or 10 h, on the solubility of sarcoplasmic and myofibrillar proteins, soluble non-protein nitrogen, and on the water-holding capacity, colour, tenderness and microbiological status of the meat, was assessed. Comparisons were made with the same traits measured on non-stimulated controls (average muscle temperature, 5°C), which were cold-deboned post rigor, and with hot-deboned, electrically stimulated muscles, subsequently held at 2°C. For each treatment and its corresponding control, six muscles each were studied. Such electrical stimulation produced a typical acceleration of pH fall post mortem and enhanced ageing changes at both 30°C and 40°C. It significantly increased tenderness over non-stimulated, cold-deboned controls. The higher temperature of ageing, however, was significantly associated with adverse colour development, loss of water-holding capacity and increased microbial growth. Electrical stimulation alone would not obviate the need for immediate refrigeration in hot-deboning operations with ambient temperatures of ～ 40°C.     

The biochemical and physical effects of electrical stimulation on beef and sheep meat tenderness

Application of electrical stimulation in the sheep and beef processing industry has been erratic around the world and this may reflect an incomplete knowledge of how to optimise the technology. Although it is well established that stimulation increases the rate of post-mortem glycolysis, other biochemical and biophysical effects have been implicated with the use of this technology. This review seeks to examine the current theories about the effect of stimulation on post-mortem muscle. The classical view that stimulation prevents muscle from shortening excessively during rigor development has been expanded to include the possibility that it also results in physical disruption of muscle structure. The interaction of these effects with the acceleration of the rate of proteolysis through activation of the calpain protease system has not been comprehensively reviewed in the past. Thus there are two mechanisms which could explain the effect of stimulation on tenderisation, reduced 'cold-induced' shortening and alteration of protein structure. A secondary effect is the enhancement of the rate of proteolysis stimulated by release of Ca (2+) at a higher temperature. As a result of this review we highlight several areas that may prove fruitful for further research. The challenge for further development of electrical stimulation systems is optimisation of the activation of the enzyme systems in parallel with manipulation of chilling regimes so as to ensure rigor mortis is achieved at temperatures which minimise shortening. These optimal temperatures largely established at a fixed incubation temperature for detached muscle may be different when measured in intact carcasses. The potential of regional stimulation of sections of the carcass to achieve this outcome is worthy of study given the different fibre composition of muscles and temperature gradients. In addition, to ensure that appropriate amounts of energy are applied to individual carcasses, development of self-response stimulation units, which are able to determine carcass resistance and apply appropriate durations or strengths of stimulation is worthy of future research. This would lead to more effective electrical stimulation practices.     

Effect of electrical stimulation, high temperature conditions and ageing on muscle myofibrillar proteins

Electrical stimulation, when accompanied by high temperature incubation, was found to lower the extractability of myofibrillar proteins and increase their degradation, particularly that of the myosin component. Troponin T and myosin light chain 2 were similarly affected. Troponin T and troponins I and C were degraded earlier during ageing in electrically stimulated muscles incubated at high temperature than in conventionally chilled muscles.     

Effects of electrical stimulation on post-mortem changes in the activities of two Ca dependent neutral proteinases and their inhibitor in beef muscle

Post-mortem changes in the activities of two calcium-dependent neutral proteinases and their inhibitor were studied in electrically stimulated and control beef Longissimus dorsi muscles.During meat conditioning in control muscles the activity of the high-calcium-requiring proteinase (mmCa ANP) was not affected while a decrease in the activities of the low-calcium-requiring proteinase (μmCa ANP) was observed.After electrical stimulation, the mmCa ANP activity was only slightly decreased, but the μmCa ANP and the inhibitor activities were drastically affected. An 80% decrease in μmCa ANP activity was observed 4 h post electrical stimulation. The post-mortem changes seem to be closely related to the post-mortem pH fall.If the Ca-requiring neutral proteinases are involved in the meat ageing mechanism, it eems that the μmCa ANP is more likely to cause most of the post-mortem changes in the myofibrillar proteins, taking into account the low level of intracellular calcium. But as its activity is drastically reduced during the rigor mortis process, most of the effect of μmCa ANP could occur at the very beginning of the post-mortem changes.     

Comparisons of the effect of electrical stimulation methods on postmortem pH decline in beef muscle

Results of four electrical stimulation (ES) studies were summarized to demonstrate the impact of different ES parameters on pH decline patterns in postmortem M. longissimus thoracis et lumborum. Postmortem pH decline was modeled as a non-linear function of time, and estimates of minimum obtainable pH, pH decline rates, and time to reach pH 6·0 were compared for each study. The decline model for study 4 (AC, 60 Hz, 50 V; 5 min post mortem) had a larger (P < 0·05) estimate for decline rate than that for study 1 (AC, 60 Hz, 400 V; 1 h post mortem) and the control (non-stimulated) data. The model estimate of time to pH 6·0 (0·56 h) for study 4 was the shortest (P < 0·05) for all treatments. Different ES parameters produce different pH decline patterns post mortem and, therefore, may impact product quality and fabrication and chilling protocols adopted in fresh beef processing.     

The electrical stimulation of beef carcasses

Beef carcasses were stimulated shortly after slaughter at varying voltage, pulse frequency and duration, with the aim of accelerating the fall of pH, destruction of ATP and onset of rigor in the muscles, so that the meat could be chilled rapidly after slaughter without danger of cold-shortening. Optimal effects were produced at 700 V, 25 Hz for 2 min, to give a total of 3000 pulses. In undressed carcasses stimulation induced a pH fall to 6.0 within 1 h of slaughter and to 5.7 within 2.5 h in the major muscles of the forelimb, back and thigh, representing a gain of more than 8 h over the time required in unstimulated carcasses hanging at 16°C. Similar results were obtained with dressed carcasses and sides, after allowing for the 50 min or so lost in dressing. The apparently high rate of pH fall from 6.3 to 5.7 after stimulation had ceased, compared with that over the same pH range in unstimulated carcasses, can be attributed mainly to the different muscle temperatures in the two cases (38 and 26°C respectively, in four major muscles). The muscles of stimulated carcasses showed no deleterious effects of stimulation. The observed drip loss from the hindlimb jointed 6 days after slaughter was not significantly greater than that from unstimulated carcasses.     

Effects of low-frequency electrical stimulation on beef tenderness

The application of 2 Hz, 500 V electrical stimulation to early post-mortem beef sides causes rapid muscle glycolysis, yet produces no trace of the extensive tissue rupture effected by 60 Hz current. By means of this low frequency technique, coupled with a mild or delayed-chill routine, we have examined the supposed tenderizing effect of rapid pH decline alone, without concurrent fiber fracture or cold-shortening intervention. Loin steaks from sides receiving this treatment were significantly tougher than those from paired control sides, an observation strongly suggesting that tenderization is hindered by rapid glycolysis. In other experiments, 60 Hz 500-V current was found to produce very extensive fracturing with breaks appearing (on average) every 6 mm of fiber length; this treatment resulted in a very significant tenderizing relative to that observed in the unstimulated control sides. It is concluded that, apart from its ability to prevent cold-shortening, normal-frequency high-voltage stimulation exerts its beneficial tenderizing action by fracturing the fibres; the accompanying acceleration of glycolysis actually causes a small, but definite, negative effect on eating quality.     

High pre rigor temperature limits the ageing potential of beef that is not completely overcome by electrical stimulation and muscle restraining

Two simultaneous trials were conducted to determine the effects of electrical input [electrical stunning and stimulation (ES)], wrapping, pre rigor temperature (15 °C and 38 °C) and different post rigor chilling rates on beef quality using M. longissimus lumborum (n=100). The high pre rigor temperature induced a faster pH decline than ES. The loins at 38 °C had significantly greater protein denaturation, more purge and drip loss, higher shear force values and less desmin degradation compared with the loins at 15 °C. No difference in sarcomere length was determined between the pre rigor temperatures regardless of ES and wrapping. Different post rigor chilling rates did not play a substantial role in water-holding capacity, proteolysis, or shear force values during ageing. These results suggest that high pre rigor temperature induces temperature-related toughness of muscle due to protein denaturation with subsequent limitation of proteolysis by μ-calpain, regardless of ES and wrapping treatments.     

The influence of high temperature, type of muscle and electrical stimulation on the course of rigor, ageing and tenderness of beef muscles

The course of rigor mortis (rigor), ageing and tenderness has been evaluated for three beef muscles; M. biceps femoris (BF), M. semimembranosus (SM) and M. semitendinosus (ST), when entering rigor at constant temperatures of 15 and 37°C respectively, with and without electrical stimulation (ES/NS) (85 V, 14 Hz and 32 s). The course of post-mortem changes has been registered by isometric tension, by shortening of unrestrained muscle strips and by following the pH decline and the changes in metabolites, such as ATP and CP. Ageing at +4°C was recorded by measuring Warner-Bratzler (W-B) shear values 2, 8 and 15 days post mortem. On the last occasion, the sensory properties of the cooked meat were also evaluated. Maximum shortening and isometric tension were higher at 37°C as compared to 15°C, whereas ES did not reduce rigor shortening. A high correlation between maximum shortening and the ATP-level at the onset of the shortening rapid phase was found (r = 0·77(???)), which could explain the greater shortening obtained at 37°C compared to 15°C. Rigor shortening is an important phenomenon governing meat tenderness as tenderness is highly affected by rigor temperature but not by ES. This was the case for muscles SM and ST but not for BF muscle. Even though tenderness was measured after ageing (15 days post mortem), shortening during rigor seems to be more important for toughness when rigor mortis occurs at 37°C than any suggested tenderizing effect due to increased proteolysis in this temperature region.     

The effects of electrical stimulation and ageing on beef tenderness

Seventeen beef carcasses from cattle with a range of breeds, ages and body conditions were used in this trial. The four treatments applied to each carcass were control (C), electrical stimulation (ES), ageing for 28 days (A) and electrical stimulation plus ageing for 28 days (ES + A). Post-mortem muscle pH was measured at 0, 0·5, 4 and 24h post-stimulation. Significantly lower muscle pH values (P < 0·01) were achieved by the stimulated carcass side sompared to the unstimulated side at 0·5 (pH 6·47 vs. 6·91) and 4 h (pH 5·96 vs. 6·44) post-stimulation.

Warner-Bratzler shear and taste panel methods were used to assess the tenderness of Longissimus dorsi muscle samples from each of the four treatments. The ES, A and ES + A treatments were significantly more tender (P < 0·01) than the control treatment. The ES and the A treatments resulted in a similar improvement in tenderness compared to the control. The ES + A treatment was significantly more tender (P < 0·01) than the ES treatment alone, but there was no significant difference in tenderness between the A and the ES + A treatments.     

Hot deboning beef with and without electrical stimulation

Two hot deboning procedures for producing vacuum packed primal beef joints were compared with conventional side chilling followed by cold deboning. Cold shortening toughness was avoided in the hot procedures either by a delay before chilling or by electrical stimulation of the carcass. Overall evaporative losses were 0·6% with hot deboning and 1·9% with cold deboning. Hot deboning reduced drip loss but the effect was smaller after electrical stimulation. The colour of large muscles which cool unevenly on the side was more uniform after hot deboning, but again the improvement was smaller after electrical stimulation. There was no difference in bacterial contamination or growth on hot and cold deboned meat, and instrumental and sensory assessments confirmed that eating quality was similar for all three treatments.     

The influence of low temperature, type of muscle and electrical stimulation on the course of rigor mortis, ageing and tenderness of beef muscles

The course of rigor mortis, ageing and tenderness have been evaluated for two beef muscles, M. semimembranosus (SM) and M. longissimus dorsi (LD), when entering rigor at constant temperatures in the cold-shortening region (1, 4, 7 and 10°C). The influence of electrical stimulation (ES) was also examined. Post-mortem changes were registered by shortening and isometric tension and by following the decline of pH, ATP and creatine phosphate. The effect of ageing on tenderness was recorded by measuring shear-force (2, 8 and 15 days post mortem) and the sensory properties were assessed 15 days post mortem. It was found that shortening increased with decreasing temperature, resulting in decreased tenderness. Tenderness for LD, but not for SM, was improved by ES at 1 and 4°C, whereas ES did not give rise to any decrease in the degree of shortening during rigor mortis development. This suggests that ES influences tenderization more than it prevents cold-shortening. The samples with a pre-rigor mortis temperature of 1°C could not be tenderized, when stored up to 15 days, whereas this was the case for the muscles entering rigor mortis at the other higher temperatures. The results show that under the conditions used in this study, the course of rigor mortis is more important for the ultimate tenderness than the course of ageing.     

电刺激对牛肉品质影响研究进展

电刺激是一种通过给畜禽胴体进行电流刺激而加快肉类成熟的技术。该项技术对于宰后牛肉品质有重要影响。目前已有学者对电刺激的作用机理进行了广泛研究,最近在pH-温度窗口理论以及电刺激对肉色和保水性的影响方面有了最新进展。文中首先介绍了pH-温度窗口理论,随后总结了电刺激对胴体的pH值变化、细胞骨架蛋白降解以及肌原纤维结构变化等方面的影响及因此对牛肉品质产生的影响,以此对国内肉牛屠宰企业合理运用电刺激技术提供理论指导。     

Postcooking temperature changes in beef patties

Beef patties (86 and 143 g) formed from high-fat (20 to 29%) and low-fat (6 to 10%) ground beef obtained in eight different selections for both high and low fat content were cooked by either a gas grill or an electric griddle. Patties were cooked to either 66.1 or 68.3 degrees C as determined in the thickest section, and internal temperatures were recorded after cooking at 1-s intervals for 180 s in both thick and thin sections of patties. Time-temperature curves (after cooking) were evaluated for compliance with regulatory requirements for classifying patties as fully cooked. For patties cooked to 66.1 degrees C, the maximum highest temperature in the thickest patty section often did not reach 71.1 degrees C (recommended for cooking of beef patties by consumers). Although thin sections of patties had higher temperatures than thick sections at the termination of cooking, temperature variability was greater and declines in temperature occurred sooner in thin patty sections. Failure to meet fully cooked, time-temperature requirements was greater in thin than thick sections. Thicker (143-g) patties possessed longer postcooking times before declining in temperature than thinner (86-g) patties. Although many beef patties cooked in this study achieved regulatory time requirements for maintaining 66.1 or 68.3 degrees C (as well as attaining 71.1 degrees C), some patties did not meet these requirements. Because of the considerable temperature variability that can exist within patties at the conclusion of cooking, use of end point temperatures of less than 71.1 degrees C is not recommended for consumers. Consumers should allow several minutes of holding following cooking before consumption to maximize the increases in postcooking temperature. Further research is required to establish cooking procedures that will improve temperature uniformity and eliminate "cold spots" during cooking of beef patties.     

Effects of temperature on post-mortem metabolism in beef muscle

Changes in pH and in the levels of some phosphate fractions with time were examined in beef muscle stored at 1°, 15° and 37° soon after slaughter. At 15° the fall in pH of the muscle and decreases in concentration of creatine phosphate and of other acid-labile phosphate occurred more slowly than at 37° and there was also a slower increase in the concentration of inorganic phosphate. Not all of these changes occurred more slowly at 1° than at 15°, however. The alkali-labile phosphate concentration remained virtually constant at 37° but increased at each of the other two temperatures, the increase at 1° being greater than that at 15°. These changes in alkali-labile phosphate concentration were attributable to the accumulation of hexose-6-phosphate. An effect of temperature on the metabolism of an organic phosphate fraction stable to both acid and alkali was noted.     

Low voltage electrical stimulation and post-mortem energy metabolism in beef

In the present study, the influence of low voltage electrical stimulation on glycolysis, concentrations of creatine phosphate and adenine nucleotides, as well as the relationship between metabolic activity and tenderness, was examined in bovine M. longissimus dorsi. During stimulation, about 50% of the creatine phosphate was consumed and the immediate pH drop was, on average, 0·21 units. The increased energy consumption resulted in a decrease in the halftime of ATP from 10 h in non-stimulated muscles to 5 h in electrically stimulated muscles. The total high energy phosphate turnover was found to be 2400 μmol/h/g during stimulation and 18 μmol/h/g immediately following stimulation compared with 9 μmol/h/g for the non-stimulated counterpart. No obvious abnormalities were found in the course of changes during energy metabolism following stimulation, besides the increased metabolic rate. Significant relationships were found between the degradation of several of the energy metabolites during stimulation and improvements in tenderness. It is concluded that, within the variation found in this study, the better the effect of electrical stimulation in increasing the metabolic rate, the better the resulting meat tenderness. Results also showed that the higher the shear force in the non-stimulated part, the better was the effect of electrical stimulation in improving the meat tenderness.     

Effect of electrical stimulation on the rheological properties of rabbit skeletal muscle

The effect of electrical stimulation on the rheological properties of rabbit skeletal muscle after death was investigated. The extensibility of electrically stimulated psoas muscles decreased more rapidly than that of non-stimulated muscles. For raw non-stimulated longissimus thoracis muscles excised from the carcasses immediately after slaughter, the penetration force required was greatest 24 h after slaughter and then decreased slightly after 168 h. The corresponding force for stimulated longissimus thoracis muscles increased to a maximum in 12 h and then decreased to values less than non-stimulated muscles. However, in the case of raw longissimus thoracis muscles whichhad been attached to the skeleton until measurement, there was no significant difference in penetration force between stimulated and non-stimulated muscles. In cooked muscles, electrical stimulation resulted in lower penetration forces at 24 h post mortem, but on further storage the differences decreased.     

Effect of electrical stimulation on post mortem biochemical characteristics and quality of Longissimus dorsi thoracis muscle from buffalo (Bubalus bubalis)

High voltage electrical stimulation (700 V, 1400 V peak, pulses 1 s on/1 s off, 60 Hz, 2 A) on buffalo carcasses resulted in a significantly more rapid pH fall in Longissimus dorsi thoracis muscle when compared to non stimulated controls (p < 0.01), during the first 24 h after slaughter. The IMP/ATP ratio on the same period showed a much more rapid increase for the stimulated muscles (1.07 and 1.16 at times 1 and 2.5 h post mortem vs control values of 0.77 and 0.83, respectively). Sensory and instrumental evaluation of texture of meat cooled by two distinct processes showed that tenderness at 24 h post mortem was higher in the stimulated muscles compared to non-stimulated controls, irrespective of the cooling process adopted. High voltage stimulation significantly decreases cohesiveness, increases myofibril fragmentation; and SDS polyacrylamide gel electrophoresis of the myofibrillar proteins showed a weakening of Troponin T band during 6 days of ageing in non-stimulated control muscles, whereas electrical stimulation accelerated the process of ageing over 3 days. This is the first report on acceleration of conditioning in buffalo muscle and the conditions described here have a high potential for application in meat industry for buffalo slaughter.     

The effect of time and type of electrical stimulation on the calpain system and meat tenderness in beef longissimus dorsi muscle

Effects of type and time of electrical stimulation on the calpain system, sensory and objective meat quality in the M. longissimus thoracis et lumborum from 38 pasture-fed carcasses, were investigated under conventional chilling conditions. High voltage stimulation was applied to whole carcasses at 3 min post-mortem (pm) and to sides at either 40 or 60 min pm, whilst low voltage stimulation was applied to whole carcasses at 3 min pm and to sides at 40 min pm. Unstimulated sides served as controls. The levels of extractable μ-calpain and calpastatin decreased during stimulation by 28-44% and 8-17%, respectively. Shear force and adjusted tenderness score showed that stimulation at 3 min, irrespective of type of stimulation, resulted in significantly tougher meat (P<0.05) which was associated with an rapid rate of pH decline, compared to stimulation at 40 min. Higher calpastatin levels soon after stimulation at 3 min (P < 0.05) and lower μ-calpain level at 24 h pm for high voltage stimulation at 3 min (P<0.05) coincided with the tougher meat. On the other hand, high voltage stimulation at 40 and 60 min resulted in similar tenderness and levels of μ-calpain and calpastatin post-stimulation and 24 h pm. Significantly tougher meat from the control sides, with a higher μ-calpain levels at 24 h pm and similar sarcomere length, compared to those from low voltage stimulation at 40 min (P<0.001), appeared to be linked to the later activation of the calpain system. Results from the current study suggest that early application of stimulation may be associated with a very rapid decline in pH and consequently a reduction in meat quality.