The protective effect of electrical stimulation and wrapping on beef tenderness at high pre rigor temperatures

A three factorial experimental design involving electrical stimulation (ES/NES), wrapping (wrapped/unwrapped) and pre rigor temperature (15 °C or 35 °C) was applied to 70 beef M. longissimus lumborum muscles to obtain a wide variation in shear force and drip loss. The shear force of all treatment groups decreased during ageing. As anticipated, wrapping and electrical stimulation had positive effects on shear force. However, high pre rigor temperature (35 °C) did not result in higher shear force values if the muscles were electrically stimulated, wrapped or both. The results suggested that electrical stimulation protects against the negative effects of high pre rigor temperatures. The drip loss of all treatment groups increased during ageing in a manner that was unrelated to treatment but was correlated to tenderness (r² = 0.70; p < 0.0001). It was concluded that the application of electrical stimulation, whatever the pre rigor temperature, protects beef from toughening through the prevention of rigor shortening and the avoidance of inhibition of ageing enzymes.     

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.     

Examination of the effect of ageing and temperature at rigor on colour stability of lamb meat

A study of factors (ageing period, rigor temperature and vitamin E level) impacting on the colour stability of lamb m. longissimus thoracis et lumborum (LL) during 3 days of simulated retail display was undertaken. The LL were taken from 84 lambs from 3 slaughters. Slices of LL were measured fresh (24 h post-mortem) or after ageing for 5 days in vacuum packaging. The oxy/met ratio (630/580 nm), declined with display time, and increased with increasing temperature at pH 6.0. Redness (a*) values also declined with display time and a reduction in redness values was observed as LL pH at 24 h post-mortem and/or pH at 18 °C increased. There was no effect of ageing period or vitamin E level on the oxy/met ratio or a* values when the vitamin E level averaged 3.76 mg/kg LL. These results suggest that maximising vitamin E levels in lambs and achieving a moderate rate of pH decline will optimise colour stability irrespective of ageing period.     

Effect of concentrate feeding on instrumental meat quality and sensory characteristics of fallow deer venison

Venison from twenty four hybrid fallow deer does, 36 months old with an initial body condition score (BCS) of 2, was tested to determine the influence of feed type on meat quality. Feeding with concentrates increased BCS (P < 0.01) but did not affect ultimate pH (P > 0.05). BCS 4 animals had higher intra muscular fat (IMF) (P < 0.01), and more tender meat (P < 0.05). Venison from does fed over 24 weeks exhibited less redness (P < 0.01) than those fed for 19 weeks regardless of feed type.Panellists evaluated samples for colour, flavour, tenderness, juiciness and overall liking. They detected significantly (P < 0.05) stronger flavour in meat from animals fed concentrates. Male panellists detected flavour differences within meat from animals fed concentrates (P < 0.05), with longer feeding periods resulting in stronger flavour. There was no difference in overall liking, therefore finishing fallow deer on grain-based concentrate feeds prior to slaughter provided little commercial advantage.     

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.     

The impact of new generation pre-dressing medium-voltage electrical stimulation on tenderness and colour stability in lamb meat

Previous work identified that a large number of domestic lamb carcases processed in Australia do not meet the recommended pH/temperature window during chilling. New medium voltage electrical stimulation technology has been developed to alleviate this problem. This study used an optimised setting (800mA with a pulse width 0.5ms) to evaluate the effects on meat quality with a focus on tenderness and meat colour. In total 40 (electrically stimulated) and 40 (non electrically stimulated) lambs from 11 lots killed over 2 days were evaluated. There was a significant difference (P<0.05) between stimulation treatments for initial pH, rate of pH decline and the predicted temperature at pH 6.0. There was also a large difference in the number of carcases that met the recommended window (pH of 6.0, between 18 and 25°C), with an average 67.5% of stimulated carcases and 25% of unstimulated carcases meeting or falling just above the recommended window. The stimulation treatment had no significant (P>0.05) effect on sarcomere length or myofibrillar fragmentation index (MFI) of the m. longissimus (LL). After 1day of ageing LL samples from stimulated carcases had a significantly lower (P<0.05) shear force than non stimulated samples, but there was no difference between stimulation treatments after 5 days ageing. However, ageing period did have a significant effect (P<0.001) on both MFI and shear force, such that 5days aged product had higher MFI and lower shear force values. There were minimal effects of stimulation on colour stability.     

Consumer evaluation of venison sensory quality: Effects of sex,body condition score and carcase suspension method

Intact fallow bucks (n = 20) and non-pregnant fallow does (n = 24) (Dama dama), in the body condition score (BCS) of 2, 3 and 4 (lean, prime and fat) and rising 2 year old red deer stags (n = 26) (Cervus elaphus) of the same BCS range (2–4) were used in this study to determine the impact of sex, BCS and method of carcase suspension on consumer perception of venison quality. Consumers were asked to evaluate cooked meat samples (M. gluteus medius) on an unstructured line scale for colour, flavour, tenderness, juiciness and overall liking. Meat from both fallow deer and red deer was preferred by consumers when carcases had hung by the pelvic suspension (PS) method compared with the Achilles tendon (AT) method of hanging (p < 0.001). Consumers also noted a difference in colour between sexes in fallow deer venison, with venison from 36 month-old does being darker (p = 0.015), and preferred venison from does over 18–24 month-old bucks. There was a significant difference in the consumer scores for tenderness in red deer stags of BCSs 2 and 4 (p = 0.05) with panellists determining BCS 4 animals to be more tender; however no tenderness differences were observed for fallow deer does compared with bucks.     

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.     

Alternating frequency to increase the response to stimulation from medium voltage electrical stimulation and the effect on objective meat quality

The use of alternating frequencies during stimulation can increase stimulation response of a medium voltage electrical stimulation unit (MVS) by increasing the rate of pH decline. Various combinations of frequency modulation were tested in experiment 1 to determine the treatment resulting in the greatest stimulation response; the lowest initial pH, fastest rate of pH decline, highest temperature at pH 6 and the highest number of carcasses with a pH of 6 by 25(o)C and the treatment achieving the highest number of carcasses in the pH temp window (temperature at pH 6 between 18-25(o)C). The objective meat quality of these treatments compared to an unstimulated treatment was tested in experiment 2. Modulating the frequency (Hz) across the 6 segmented electrodes of the MVS by 10, 15, 25, 10, 15, 25Hz (Treatment 6, using a pulse width: 2.5ms, current: 1A) resulted in the greatest stimulation response. This treatment may be suitable for abattoirs that hot bone sheepmeat and require fast pH declines to ensure minimal cold shortening of meat. However, this treatment did not result in the tenderer meat despite the higher stimulation response. This treatment may have induced a greater number of contractions overall and therefore a greater pH decline response but resulted in less myofibrillar disruption compared to the other treatments due to a concomitant decreased force of contraction thus reducing potential tenderisation. Maintaining a constant frequency of 15Hz (Treatment 1; pulse width: 2.5ms, current: 1A) resulted in a higher number of carcasses in the pH temp window required (temperature at pH 6 between 18-25(o)C) in part A (P<0.05) and in addition to the higher tenderness levels this treatment may be more appropriate to satisfy the overall demands of abattoirs using these systems. This paper has also demonstrated electrical stimulation results in tenderer meat compared to unstimulated meat even after 30d of ageing (2.53±0.4 compared to 2.85±0.1 for the loin (M. longissimus thoracis et lumborum) (P<0.01) possibly due to a protective benefit of stimulation on meat tenderness. Overall, no detrimental effects of modulating frequency were observed on drip loss or retail colour display despite a greater rate of colour change observed with the modulated frequency treatment and the longer aged product.     

Effects of electrical stimulation, chilling temperature and hot-boning on the tenderness of bovine muscles

The objective of this study was to determine the effects of hot-boning, low voltage electrical stimulation (ES) and chilling temperature on the tenderness of bovine M. longissimus dorsi (LD) and M. semimembranosus (SM) muscles. LD (n=32) and SM (n=32) muscles were subjected to different post-mortem treatments; hot-boning (before 90min post-mortem), cold-boning (at 48h post-mortem), low voltage ES and rapid or slow chilling. Hot-boned muscles which were not electrically stimulated (NES) had higher Warner Bratzler shear force (WBSF) values (P<0.001) and shorter sarcomeres (P<0.001) than cold-boned muscles. Hot-boned muscles subjected to ES had lower pH values (P<0.001) post-stimulation and up to 8h post-mortem than NES muscles. At both chilling temperatures WBSF values were lower in ES hot-boned LD and SM muscles at days 2, 7 and 14 post-mortem than NES muscles. Hot-boned muscles subjected to slow chilling had longer sarcomeres (P<0.001) than those subjected to fast chilling. In hot-boned SM muscles, ES resulted in longer sarcomere lengths (P<0.001). However, ES did not have a significant effect on the sarcomere length of LD muscles. As indicated by WBSF values all muscles tenderised during ageing, including muscles which were 'cold shortened'. Proteolysis was not the main reason for differences in WBSF values between ES and NES muscles as judged by qualitative sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). A combination of slow chilling and ES had a positive effect on hot-boned muscles with respect to WBSF values.     

Effect of electrical stimulation on quality of tenderstretched chevon sides

Thirty male Black Bengal goats 5-8 years of age, slaughtered at the Kolkata slaughter house, India, by the traditional 'halal' method, were used to assess the effect of electrical stimulation on tenderstretched sides of chevon carcasses. Five groups (T1, T2, T3, T4 and T5) were treated with variable voltages of 35, 110, 330, 550, 1100 with fixed 50Hz and 10pulses/s for a duration of 3min. Different quality parameters, such as, fibre diameter, sarcomere length, water holding capacity (WHC), pH, microbial content and taste panel score were studied at 24 and 48h post-stimulation. pH, WHC and fibre diameter decreased whereas sarcomere length showed an increasing trend in electrically stimulated meat, which was also microbiologically more stable. The non-stimulated control meat was tougher than the electrically stimulated chevon as evident through taste panel scoring. Treatment 3 (T3), i.e. 330V, 50Hz and 10pulses/s, showed superiority over the other four treatments in the majority of the important meat quality parameters.     

Effects of transport time and rest period on the quality of electrically stimulated male cattle carcasses

Forty-five castrated Nelore-breed male cattle, with average age of 37 months, were randomly chosen. The cattle were submitted to the combination of two transport times (up to 2 h and approximately 5 h) and five rest periods (0 h, 6 h, 12 h, 18 h and 24 h). The carcasses were electrically stimulated. After 24 h postmortem, the average of the ultimate pH in the M. Longissimus dorsi (LD) was considered normal (5.57–5.72) for eight out of nine cattle groups. The shear force (SF) was higher for cattle that were not allowed a rest period (0 h) on both transport times, however it was not significant (p > 0.05). This result was compatible with the sarcomere length (SL), which were shorter for those carcasses. The rest period and transport time had no influence on the L^∗ (lightness) values, but a^∗ (redness) values increased until the 12th hour of rest. The b^∗ (yellowness) value was negative for the cattle without a rest period (0 h) and transported for 5 h. The cattle transported for up to 2 h could be allowed a 6-h rest period only, and the cattle transported for 5 h could be allowed a 12-h rest period without the meat quality being affected significantly.     

Combination of low voltage electrical stimulation and early postmortem temperature conditioning on degradation of myofibrillar proteins in Korean native cattle (Hanwoo)

The combination effect of low voltage electrical stimulation (LVES) and early postmortem (PM) temperature conditioning (2, 16, and 30°C until 3 h PM) on degradation of myofibrillar proteins were determined from Korean native cattle (Hanwoo). Myofibrils were removed at 1, 2, 3, 7, and 14 days of PM storage (2°C) and analyzed for titin, nebulin, desmin, and troponin-T by SDS-PAGE and by Western blot analysis. Degradation rate of myofibrillar proteins was affected by the combination of LVES and temperature conditioning. LVES-30°C treatment resulted in faster degradation of titin, nebulin, desmin, and troponin-T during PM storage than the other treatments. Degradation of titin took place more slowly than nebulin, desmin or troponin-T.     

Reassessing the principles of electrical stimulation

The mechanisms by which electrical stimulation (ES) of carcasses can be used to modulate meat quality are reviewed. Evidence to support an effect of ES on tenderness (and other meat quality attributes) based solely on changes in the pH/temperature profile within carcass muscles are presented. The interactions between electrical parameters and the contraction responses of carcass muscles are described to provide generalised principles to guide the design of electrical stimulation technology. The commercial risks to meat quality of inappropriate use of electrical stimulation, particularly excessive stimulation to produce PSE-like conditions, are considered.     

Effect of pelvic suspension on the instrumental meat quality characteristics of red deer (Cervus elaphus) and fallow deer (Dama dama) venison

The effect of pelvic and Achilles tendon suspension of red and fallow deer carcasses on meat quality parameters were compared. Venison was evaluated from red deer stags (n = 14), bucks (n = 14) and fallow deer does (n = 10) between 12 and 36 months old. Immediately after slaughter, carcasses were split down the dorsal midline and assigned to one of the two hanging methods and pH and core body temperature measured. Twenty-four hours post-slaughter muscles were excised. Venison from fallow deer and red deer stags pelvic-suspended had significantly lower (P < 0.001) cooked shear force values than Achilles hung carcasses. There was no significant difference between hanging technique for other characteristics measured. These data indicated that pelvic suspension should be adopted by the deer industry to increase tenderness of venison.     

Effect of low-voltage electrical stimulation after dressing on color stability and water holding capacity of bovine longissimus muscle

The effect of low voltage electrical stimulation after dressing (ES) on color stability and water holding capacity (WHC) of beef was investigated. Nine Swedish red cattle were slaughtered and the left side was electrically stimulated (80 V, 35 s) approximately 30 min after stunning, whereas the other side was not treated and used as control. Color and its stability, WHC, and protein solubility were evaluated on longissimus lumborum muscles from the two sides. ES produced a brighter red color at 24h mainly by increasing the oxygenation capacity of myoglobin (P<0.01), which was attenuated by postmortem aging. ES did not affect WHC, protein solubility and color stability (P>0.05). Therefore, this technology could accelerate meat tenderization without any negative effect on commercial attributes, such as color or drip of bovine longissimus muscle.     

SmartStretch™ technology. III. The impact of medium voltage stimulation and SmartStretch™ technology on sheep topside (m. semimembranosus) meat quality traits under commercial processing conditions

This study evaluated the interaction between medium voltage electrical stimulation, SmartStretch™ stretching and ageing treatments on key meat quality traits of hot boned sheep m. semimembranosus. Medium voltage stimulation reduced initial pH (P < 0.001), but did not impact on other meat quality traits. There was a significant interaction between stretch treatment and ageing (P < 0.001) for shear force such that samples which were both stretched and aged were the most tender. Sarcomere length was significantly (P < 0.001) increased by SmartStretch™ treatment. Control (no stretching) resulted in greater (P < 0.05) cooking loss, but there was significantly less purge loss (P < 0.05). The ratio 630/580 nm and a* colour values at 0 and 5 days decreased at a significantly (P < 0.05) slower rate when SmartStretch™ was applied. Overall medium voltage stimulation did not inhibit the effectiveness of the SmartStretch™ treatment. The SmartStretch™ treatment provided significant improvement in tenderness and the potential to increase meat display time.     

The effects of a beta-agonist treatment, vitamin D3 supplementation and electrical stimulation on meat quality of feedlot steers

In this study, 20 young steers received no beta-agonist (C), 100 animals all received zilpaterol hydrochloride (Z), with 1 group only receiving Z while the other 4 groups received zilpaterol and vitamin D3 at the following levels (IU/animal/day) and durations before slaughter: 7 million for 3 days (3D7M); 7 million for 6 days (6D7M); 7 million for 6 days with 7 days no supplementation (6D7M7N) and 1 million for 9 days (9D1M). Left carcass sides were electrically stimulated (ES) and the right side not stimulated (NES). Samples were aged for 3 or 14 days post mortem. Parameters included Warner-Bratzler shear force (WBSF), myofibril filament length, sarcomere length and calpastatin and calpain enzyme activity. Both ES and prolonged aging reduced WBSF (P<0.001). 6D7M, 6D7M7N and Z remained significantly tougher than C (P<0.001), while 3D7M and 9D1M improved WBSF under NES conditions. ES is more effective to alleviate beta-agonist induced toughness than high vitamin D3 supplements.     

Effects of transport time and season on aspects of rabbit meat quality

The aim of this study was to determine whether transport times of up to 7 h can have a significant effect on instrumental meat quality traits in rabbits. Spain has very hot summers and cold winters; therefore, we performed replicates in two seasons. To evaluate the effect of transport time and season on rabbit meat quality, we assessed four meat quality parameters: pH, water holding capacity (WHC), texture (compression and Warner–Bratzler analyses), and colour (CIEL*a*b*). We also considered the effect of the position of the animals on the transport vehicle. After slaughter, we analysed steaks of Longissimus dorsi from all transported animals (n = 216). Average pH at 24 h and WHC did not differ significantly between transport time treatments. Position on the vehicle did not influence the measures of meat quality. Transport time had a significant effect on all the meat texture parameters measured by compression, but did not affect shear force or toughness. Transport time influenced a* but not L* or b*. Transport time had much less of an effect on meat quality than time of year; therefore the effect of season appeared to be independent of transport time. Position on the vehicle had no effect on meat quality. Based on our results, we conclude that the transport process can affect instrumental meat quality.