Effects of low voltage electrical stimulation on mature cow carcasses: Part 1-Selected quality attributes of beef

The quality characteristics of semitendinosus (ST) and longissimus dorsi (LD) roasts obtained from mature carcasses subjected to extra low voltage (50-100 V) electrical stimulation (ES) were determined. ES was applied for 2 min with voltage increases to either 50 V (ES1) or 100 V (ESII). Evaluationss were conducted on meat obtained from control sides (no ES) aged for either 48h or 7 days and from ES carcasses aged for 48h. ES caused a reduction (P < 0·1) in pH values 1 and 4h post mortem. At 24h, the pH of each of the muscles from ES and control carcasses was similar. There were no differences in raw rib-eye muscle colour, firmness or texture due to ES. Cooking losses of ST and LD did not appear to be affected by either ES or increased ageing of control roasts. For both ST and LD roasts, trained panellists generally detected no significant effects of ES or ageing time (for no ES roasts) on palatability. Consumer panel judgements of ST roasts were similar to those of the trained judges. Water-holding capacity, tenderness (OTMS) and softness (penetrometer) data for ST and LD roasts generally support findings from sensory evaluation. Cooking and eating quality characteristics of ST and LD roasts from mature cow carcasses subjected to ES were similar to those of the controls.     

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.     

Pathways of high and low voltage electrical stimulation in sheep carcasses

Using the neuromuscular blocking agent, curare, the involvement of the nervous system in the transmission of high (850 V peak) and low voltage (45 V peak) electrical stimulation in sheep carcasses was studied. Post-mortem metabolism in the Longissimus dorsi, Semitendinosus and Semimembranosus muscles was followed by measuring changes in pH, adenosine triphosphate, creatine phosphate, inorganic phosphate and hexose monophosphate. Stimulation was considered to be effective if it accelerated glycolysis. Low voltage stimulation of glycolysis was completely inhibited by curare, indicating that a functional nervous system is required for effective stimulation by low voltages. In contrast, high voltage stimulation of glycolysis was not affected by curare, indicating that high voltages exert their effect by depolarising the cell membrane directly.     

Electron microscopy of contractile bands in low voltage electrical stimulation beef

This study was designed to explore the effects of low voltage electrical stimulation and delay chilling on the ultrastructure of beef longissimus muscle. The results showed that 44.9% of sarcomeres in the ES samples had contractile zones, and 16.9% of sarcomeres adjacent to contractile zones were stretched in 100 views of electron microscopy. The ultrastructures of 60.9% of sarcomeres changed when the samples were electrically stimulated and then delay-chilled. Contractile bands play an important role in meat tenderization during postmortem aging.     

The tenderising effect of electrical stimulation of beef carcasses

Electrical stimulation (ES) of beef carcasses soon after death has an accelerated tenderising effect on the musculature, under conditions of slow cooling (8 h at 16°C and then storage in still air at 1°C). The effect is large in the LD muscles, reducing the shear force on day 1 of storage from 11 to 6 kg; on day 14, the difference is still 3·3 kg. These differences would be detected by taste panels. The St muscles show a similar, but less pronounced, effect which would probably not be detected by taste panels. The accelerated tenderisation due to ES can be accounted for by the higher temperatures obtaining in stimulated muscles at the onset of rigor. Rapid cooling soon after death reduces the effect almost to zero. Hence, the extra tenderisation cannot be due to muscle damage during ES. Histological examination shows that stimulated muscles have longer sarcomeres than the controls; they do not exhibit damage. However, with slow cooling, irregular bands of denatured sarcoplasmic protein are deposited within the fibres of stimulated muscles, similar to those found in PSE pig muscles. There is also some shortening of sarcomeres in the region of the bands. The protein is deposited on the myofibrillar surfaces. In spite of the PSE-like appearance, there is no significant increase in drip from the stimulated muscles at 48 h after death.     

The effect of high and low voltage electrical stimulation on beef quality

Meat bulls were assigned to three treatment groups—high voltage intermittent electrical stimulation, low voltage electrical stimulation and no stimulation.Both stimulation methods resulted in a significantly more rapid pH fall in the longissimus and adductor muscles during the first 8 h post mortem. Carcass cooling rates were relatively slow, since temperatures of the longissimus and adductor muscles were 15°C, respectively, at 8 h post mortem.Samples of stimulated longissimus, cut at 24h post mortem and vacuum stored at 3°C for 6 days, had a brighter red colour, higher drip and heating loss, lower shear force values and scored better in taste panels, compared with samples from control carcasses. No significant differences were observed between high and low voltage electrical stimulation in quality traits measured.Although the combined result of pH and temperature measurements during the first 8 h post mortem suggest an absence of cold shortening conditions in control carcasses, a lower sarcomere length was found in samples of the longissimus muscle taken from these carcasses at 24 h post mortem.     

Effect of low voltage electrical stimulation of pig carcasses and ageing on sensory attributes of fresh pork

The effect of electrically stimulating pig carcasses and ageing on sensory attributes of pork was evaluated in this study. A total of 48 female pigs [Duroc×Large White/Landrace (A; n=24) and Large White/Landrace (B; n=24)] were randomly allocated immediately prior to slaughter to one of two low voltage stimulation treatments; no stimulation or 150 mA applied for 30 s at 2 min post-exsanguination. Each side of the carcass was then randomly allocated to an ageing treatment of either 2 or 7 days post-slaughter. Muscle pH of the M. longissimus lumborum was lower (P<0.001) in electrically stimulated carcasses when measured from 40 min to 8 h post-slaughter compared with non-stimulated carcasses. Percentage drip loss, muscle lightness and PSE incidence were not influenced (P>0.05) by electrical stimulation. Electrical stimulation of pig carcasses and ageing pork for 7 days post-slaughter both improved (P<0.001) consumer scores for tenderness, juiciness, overall liking and quality category, however the interaction term of electrical stimulation and ageing was not significant for any of the sensory attributes. Pork from non-stimulated carcasses that was aged for 2 day post-slaughter was less tender (P<0.01) compared with pork in all other treatments. These results indicate that electrical stimulation (150 mA applied for 30 sec at 2 min post-exsanguination) was effective in improving eating quality attributes of pork, particularly when pork was aged for only 2 days post-slaughter, without detrimentally affecting colour or drip loss.     

Application of constant current, low voltage electrical stimulation systems to pig carcasses and its effects on pork quality

This study examined the effectiveness of a constant current, low voltage electrical stimulation system on improving pork quality when applied to pigs at 2 min post-exsanguination. A total of 48 female Duroc×Large White/Landrace pigs of 85–90 kg liveweight were randomly allocated immediately prior to slaughter to one of four constant current electrical stimulation treatments: control (no electrical stimulation), 50, 200 and 400 mA. Stimulation was applied to pig carcasses at 2 min post-exsanguination for 30 s. No differences (P>0.05) in WB shear force values, muscle lightness or PSE incidence of pork M. longissimus lumborum (LL) was found due to electrical stimulation treatment. Muscle pH of the LL muscle was lower (P<0.001) in carcasses in the 200 and 400 mA treatments compared to those from carcasses in both the 50 mA and control treatment groups, when measured at the various time points from 40 min to 8 h post-slaughter. Although carcasses stimulated with 200 and 400 mA had higher percentage drip loss (P<0.05) and purge (P<0.001), this was not found to impact WB shear force values, muscle lightness or PSE incidence.     

Enhancement of lean characteristics of veal carcasses by electrical stimulation

Forty Holstein vealers (approximately 16 weeks of age) were slaughtered, skinned, split longitudinally and one side was electrically stimulated (700 V, 2 A and seventeen impulses) for 1 min. Internal temperatures of the rib and round were recorded at 1 h and 24 h post mortem. Approximately 24 h post mortem, lean colour scores were assigned to the cross-section of the longissimus muscle at the 11th-12th rib interface, to the outside surface of the biceps femoris muscle and to the rectus abdominis and transverse abdominis muscles of the flank; lean texture and firmness scores were also assigned to the cut surface of the longissimus muscle. 'House grades' were assigned to each side of each carcass by plant personnel. Initial (1 h) rib and round temperatures were significantly higher for the electrically stimulated sides; however, at 24 h, neither round nor rib temperatures differed between control and electrically stimulated sides. Lean colour, firmness and texture scores for longissimus muscles were significantly (P < 0·0001) improved by electrical stimulation. Electrically stimulated sides also had lighter lean colour scores in the rectus and transverse abdominis and biceps femoris muscles. Electrical stimulation increased the number of carcasses receiving the top 'house grade' and reduced the number of carcasses in the lowest 'house grade'. These data indicate that electrical stimulation will improve lean colour, firmness and texture of veal carcasses when ribbed and evaluated after a 24 h chill.     

High voltage electrical stimulation enhances muscle tenderness, increases aging response, and improves muscle color from cabrito carcasses

Our study examined high and low voltage electrical stimulation and postmortem storage as strategies to improve tenderness and lean color in cabrito carcasses. Boer cross (n=60) kids were assigned to either high (550 V), low (20 V), or no electrical stimulation treatments. No differences in muscle temperature were observed between treatments at any time measured. Muscle pH declined fastest in high voltage treated carcasses. High voltage electrical stimulation slightly increased (P<0.05) b^* and a^* in the M. gluteus medius and tended to increase L^* and b^* (P=0.06 and 0.11, respectively) values in the M. longissimus thoracis. Electrical stimulation had no effect on myofibril fragmentation at 1-, 3-, or 14-d postmortem or sarcomere length. High voltage electrical stimulation increased (P<0.05) tenderness at 1- and 3-d postmortem, but not at 14-d postmortem. Aging for 3 d did not affect tenderness regardless of stimulation treatment, but aging time for 14 d improved (P<0.05) tenderness. These data indicate that high voltage electrical stimulation and 14 d aging were effective in improving the tenderness of meat from cabrito 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.     

低压电刺激对不同部位宰后牦牛肉肌原纤维蛋白水解的影响

研究电刺激对不同部位牦牛肉宰后成熟过程中微观结构及肌原纤维蛋白水解的影响。将牦牛宰后5min内进行低压电刺激(21V,50Hz,90s)并冷却排酸,于宰后0、1、3、5d取前部肱三头肌(TB)中部背最长肌(ML)和后部半膜肌(SM),分析其肌节长度、肌纤维直径、MFI指数、肌原纤维超微结构和全肌肉蛋白电泳图谱。结果表明:电刺激使不同部位牦牛肉肌节长度显著变化(p0.05),肌纤维直径平均缩小6%、5%和9%;TB、ML和SM宰后0~5d MFI值分别上升54%、55%和92%,SM嫩度显著增大(p0.01);不同部位牦牛肉肌原纤维超微结构中挛缩带占有率分别为23.9%、26.3%和31.2%,肌原纤维结构形变溶解;SDS-PAGE电泳图谱显示,TB、ML和SM部肌原纤维蛋白均在48~75ku之间降解彻底。本研究证实了电刺激缩短牦牛肉宰后成熟时间,对不同部位牦牛肉嫩度改善,特别是对肉质较差的SM效果显著。     

井下低压电网保护装置设计

针对煤矿井下配电系统的关键设备隔爆馈电开关普遍集成度低、可靠性差、智能监控水平低等问题,基于ARM7TDMI-S内核,以LPC2210处理器为核心,以EasyARM2200作为嵌入式系统开发平台,通过对嵌入式实时操作系统的移植,设计了具有井下低压电网保护功能的智能馈电开关控制系统.该装置可以预测状态变化,为提高煤矿企业生产效率和安全作业系数提供了保证.     

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.     

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.     

Cellular heterogeneity in the response of beef to electrical stimulation

Strips of bovine sternomandibularis muscle were removed at slaughter and kept anoxic at body temperature. One strip of each pair was electrically stimulated with square wave pulses for 60 min (32 ms duration, 2Hz, <6 or 100V). Differences between stimulated and control strips were examined histochemically to determine the effect of stimulation on post-mortem glycogenolysis in different fibre types. Serial reactions for ATPase and SDH were used to type muscle fibres and the absorbance of PAS-stained glycogen was measured with a two-wavelength correction for distributional error. Relative to unstimulated control strips, fibres with strong ATPase and weak SDH reactions showed most glycogenolysis whilst fibres with weak ATPase and strong SDH reactions showed the least. Fibres with strong ATPase and strong to moderate SDH reactions showed an intermediate response. Half of the fibre populations examined had an initial increase in absorbance of PAS-stained glycogen in some or all fibres.     

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.     

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。     

Attachment of bacteria to beef from steam-pasteurized carcasses

The extent to which a bacterial cocktail containing equal numbers of Pseudomonas fragi NCTC 10689, Listeria monocytogenes BL5/2, Salmonella Typhimurium LT2, and Escherichia coli JM 109 attached to loin surface cuts (7 by 5 cm) derived from steam-pasteurized beef carcasses has been evaluated. The extent of attachment was categorized as loosely attached (removed by rinsing), firmly attached (released by stomaching), and irreversibly bound. No significant difference (P > 0.10) in the attachment of bacteria to steam-pasteurized carcasses was found compared with control loin samples that had received no treatment. No significant difference (P > 0.05) was also found in the attachment strength between the different bacterial species tested. Most bacteria inoculated onto the loin cuts were reversibly bound, since they had been removed by rinsing and stomaching. The irreversible attachment of bacteria to loin cuts was found to vary significantly (P < 0.01) among the different carcass sets used but was independent of whether the carcass had undergone steam pasteurization treatment. Use of a bioluminescent strain of E. coli showed that cells bound preferentially to cut edges and convoluted areas on the loin surface and could not be removed by rinsing. The possible mechanisms of bacterial attachment and the suitability of steam pasteurization to remove contamination incurred during slaughter are discussed.