Rigor Temperatures Research Articles

Effect of rigor temperature, ageing and display time on the meat quality and lipid oxidative stability of hot boned beef Semimembranosus muscle

The effects of rigor temperature (5, 15, 20 and 25°C), ageing (3, 7, 14, and 21days) and display time on meat quality and lipid oxidative stability of hot boned beef M. Semimembranosus (SM) muscle were investigated. Ultimate pH (pHu) was rapidly attained at higher rigor temperatures. Electrical conductivity increased with rigor temperature (p<0.001). Tenderness, purge and cooking losses were not affected by rigor temperature; however purge loss and tenderness increased with ageing (p<0.01). Lightness (L*) and redness (a*) of the SM increased as rigor temperature increased (p<0.01). Lipid oxidation was assessed using 1H NMR where changes in aliphatic to olefinic (Rao) and diallylmethylene (Rad) proton ratios can be rapidly monitored. Rad, Rao, PUFA and TBARS were not affected by rigor temperature, however ageing and display increased lipid oxidation (p<0.05). This study shows that rigor temperature manipulation of hot boned beef SM muscle does not have adverse effects on lipid oxidation.

A consumer sensory study of the influence of rigor temperature on eating quality and ageing potential of beef striploin and rump

Few consumer data are available on the effects of high rigor temperatures on eating quality of different muscles in the beef carcass. The aim of the present study was to investigate the effect of high rigor temperature (heat-toughening) on the consumer and quality traits of two beef muscles. A dataset containing consumer eating-quality scores for 3865 striploins (m. longissimus lumborum) and 734 rumps (gluteus medius) was analysed. Temperature at pH 6 (temp@pH6) was calculated for the striploin and carcasses with a temp@pH6 of &gt;35°C were classified as high rigor temperature (heat-toughened) carcasses. For short ageing periods (1–7 days), high rigor temperature striploins were assessed, by a consumer panel, as being more tender with higher overall liking and higher (more liked) flavour and juiciness, than were striploins entering rigor at a lower temperature. Beyond 14 days of ageing, the high rigor temperature striploins showed minimal improvement in tenderness and the other eating-quality attributes also showed minimal improvements. The consumer scores for tenderness, juiciness, flavour and overall liking for the rump decreased with increasing rigor temperature. High rigor temperature striploins were scored, by trained graders, to have a higher proportion of coarser and softer texture and paler colour. Carcasses defined as ‘high rigor temperature’ will show minimal ageing after extended storage and, at grading, have a higher proportion with pale colour and softer, coarser texture compared to lower rigor temperature carcasses. In conclusion, methods to reduce high rigor temperatures in beef carcasses would improve the acceptability of beef.

Muscle metabolism in sheep and cattle in relation to high rigor temperature – overview and perspective

An increasing number of Australian slaughter plants were found not to meet the Meat Standards Australia (MSA) pH–temperature window, due to high rigor temperatures, particularly at plants where grain-fed animals were slaughtered. Hence, the red meat processing industry in Australia supported a research program focused on resolving this issue, as carcasses that do not meet the MSA pH–temperature window are excluded from MSA grading. This special issue of Animal Production Science describes the outcomes of a major program identifying ante- and post-mortem factors related to heat-induced toughening in both beef and sheep meat through literature reviews and targeted research to find interventions to prevent the impact of high rigor temperature on meat quality, particularly tenderness. This paper provides an overview of the outcomes of the research program, some of which require further research before implementation. It is suggested that an entire supply-chain approach be applied to establish the most efficient and cost-effective way of reducing the incidence of high rigor temperature.

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.

Retail colour display life of chilled lamb as affected by processing conditions and storage temperature

This study explored the impact of i) processing conditions (electrical stimulation and pre rigor temperatures), and ii) storage temperature prior to retail display on the colour stability of lamb which had been vacuum-packaged for seven weeks before retail packaging in high-oxygen modified atmosphere (80% O2/20% CO2). A high pre rigor temperature (42°C) reduced colour stability while differences in colour stability between pre rigor temperatures of 5°C, 15°C and 25°C were limited. It was not affected by electrical stimulation, and did not interact with pre rigor temperature. In contrast, an increase in the storage temperature from the ideal temperature of −1.5°C to 2°C significantly decreased the colour stability of lamb loins. Even one week at 2°C at the end of the storage period had a substantial negative impact on the retail colour display life. The variability in colour increased over time, and the variability increased more for the temperature abuse treatments.

Length of exposure to high post-rigor temperatures affects the tenderisation of the beef M. longissmus dorsi

This experiment examined the effect of length of exposure of bovine M. longissmus dorsi to high temperatures (37°C) on proteolytic activity during post-mortem aging and subsequent meat tenderness. To avoid confounding between pH decline and incubation treatments, the experiment was conducted on post-rigor meat (pH &lt; 5.6), which had entered rigor at 15°C. This meat was first incubated at 15°C until rigor (pH &lt; 5.6), whereupon samples were then reheated and maintained at 37°C for 0, 1 or 3 h. Following incubation, samples were aged at 1°C for 1–21 days. Control groups were incubated at either 15 or 37°C until pH &lt; 5.6, followed by aging at 1°C. High rigor temperatures accelerated post-mortem proteolysis early in the post-mortem period, as indicated by a rapid decline in shear force (P &lt; 0.01), but post-mortem aging ceased at about day 3 post-mortem and the high rigor temperature treatment was ultimately 30% tougher at day 21 post-mortem (P &lt; 0.01). The process of reheating samples from 15 to 37°C had minimal effect on tenderness levels, but was associated with a slight increase in proteolysis, identified by myofibril length, and was associated with an increase in cook loss percentage (P &lt; 0.05). Shear force in the length of exposure experiment was affected by an incubation time × post-mortem aging interaction (P &lt; 0.01). This indicated an initial acceleration of post-mortem aging with increased length of exposure, but also a reduction in the ultimate tenderness of product after extended post-mortem aging. This was presumably due to the loss of proteolytic enzyme activity caused by the instability of proteolytic enzymes at high ionic strength conditions such as those present in post-mortem muscle.

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 ( r 2 = 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.

PEER REVIEWED PAPERS

Sharks caught in tropical Australian waters occasionally exhibit tough texture. Two species of Carcharinid shark, originally known as the sorrah shark (Carcharinus sorrah) and the black spot shark (Carcharinus tilstoni), compose the majority of the catch. Experiments were conducted to identify the cause of tough texture and to improve the overall quality of the catch. The possibility that a cold shock reaction may occur was investigated by observing the contraction of fillets under a range of temperature conditions before freezing. The effect of on-board handling practices were evaluated using frozen shark fillets, which had been stored prior to freezing in refrigerated seawater at different rigor stages, temperatures and times as trunks. Fillets were analyzed for nu-cleotides, lactate, thaw pH, sarcomere length and raw and cooked shear force values. The existence of thaw rigor was also investigated. There was little difference in the texture between the individual strips of a fillet exposed to different temperatures but there were significant differences between individual sharks. A cold shock reaction could not be demonstrated in these species. The main influences on texture were of biological origin. The species, sex and size were found to have significant links with texture of fillets. The quality of the fillets deteriorated quicker during the warmer season and were at their worst if the trunks were kept on deck till post-rigor or held in 15°C refrigerated seawater before freezing.

Factors affecting tenderness of electrically stimulated poultry

Effective electrical stimulation parameters for breast muscle of poultry deboned at the end of the processing line were determined. For experimental studies, 14.3 half sine‐wave pulses per s, 80 V peak, 10 ms duration were applied for 60 s between head and cloaca of birds removed after stunning and bleeding and then returned to the processing line. Some birds were held at a constant temperature to determine rates of pH fall. Electrical stimulation caused a fall in pH of 0.26 pH units. The rate of pH fall was accelerated, so that at 20°C, ultimate pH after stimulation was reached in 120 min versus 300 min for no stimulation and at 40°C, ultimate pH after stimulation was reached in 220 min versus 80 min for no stimulation. Unrestrained muscle entering rigor mortis at 40°C shortened by 25.4% and when entering rigor mortis at 20°C shortened by 7.6% with the mean shear force being 13.42 and 8.13 kg F, respectively. The effectiveness of electrical stimulation was determined by comparing the shortening and tenderness of breast muscles that were either left on the carcass or after cutting them from the breast bone and humerus 60 min post stimulation and aged at 0–3°C for 72 h. For cut muscles, electrical stimulation reduced muscle shortening (P < 0.05). The greatest difference in tenderness occurred between stimulated intact breasts (mean 3.34 kg F) versus cut non‐stimulated breasts (mean 13.5 kg F) (P < 0.001), but there was still a significant difference in shear force between cut non‐stimulated versus cut stimulated breasts (P < 0.05). A commercial processing line using electrical stimulation (230 V, 14.3 half sine‐wave pulses per s, 10 ms duration), via rubbing electrodes to head/neck area and legs applied for 120 s, in the post stunning and bleeding area was examined. When the breast was cut from non‐stimulated muscles at 65 min post slaughter (6.5–7°C), the meat was tough with mean shear force of 8.7 kg F (maximum 15.5 kg F), and for stimulated cut muscles, the mean shear force value was significantly lower at 3.2 kg (P < 0.001). There was no significant difference between any of the stimulated muscles cut at 65–80 min and non‐stimulated intact muscles. With low rigor temperatures at 7°C, electrical stimulation has no disadvantages and allows early deboning without toughening.

Initial chilling rate of pre-rigor beef muscles as an indicator of colour of thawed meat

The effect of three rigor temperatures and two muscles of different fibre composition on the colour of thawed meat were determined. Within 45 min post-mortem, m. semitendinosus (ST) and m. biceps femoris (BF) from unstimulated heifer sides were held at 0, 10 and 35°C until they entered rigor. The rate of pH fall was higher at 35°C than at 0 and 10°C; and the pH values were lower (first 12 h post mortem) in the ST than the BF. Hunter L*, a* and b* and the hue angle increased with increasing rigor temperature ( P<0.001). The ST was lighter and yellower and had greater hue angle than the BF. Colour parameters were plotted against the rate of muscle cooling in the first hour post mortem and linear regression lines were fitted to the data and equations were derived that gave a good indication of the colour and colour stability of the muscles as meat.

Effect of rigor temperature on muscle shortening and tenderisation of restrained and unrestrained beef m. longissimus thoracicus et lumborum

Pairs of muscularis longissimus thoracicus et lumborum (LTL) from young bulls were removed within 1 h of slaughter. Small portions of the muscles were placed in a rigormeter to continously follow the isometric tension and isotonic shortening developed, at constant temperatures of 15, 20, 25, 30 and 35°C, as the muscle went into rigor. The bulk LTL was placed in water baths at the same temperature. One of the bulk pairs was tightly restrained by wrapping, to reduce muscle shortening, the other was unrestrained free to shorten. For the bulk samples, shear values were measured using a Warner–Bratzler instrument (1, 7 and 14 days post mortem), and sensory attributes were measured using a sensory panel (7 and 14 days post mortem). Minimum tension and shortening occurred at 15°C. The activation energy for the muscle shortening process was larger than for the isometric tension process. This indicates that the isometric tension data, collected during rigor, does not solely reflect muscle shortening. Thus, a counteracting process that decreases the tension response, most likely ageing is simultaneously detected. Meat that went into rigor at 15°C had least shortening and was always more tender than meat going into rigor at higher temperatures. For meat entering rigor at temperatures higher than 15°C, restraining of the muscle by wrapping, significantly ( p<0.05) decreased the amount of muscle shortening and resulted in an improved meat tenderness ( p<0.001). It was also observed that at rigor temperatures higher than 15°C the meat tenderness is affected negatively by a reduced ageing capacity. It therefore appears that muscle shortening and enzyme activity both affect tenderness and that both are highly affected by rigor temperature and have the greatest beneficial effect at a rigor temperature of 15°C.

The effect of high post-mortem temperature on the development of pale, soft and exudative pork: Interaction with ultimate pH

The effects of post-mortem temperature and ultimate pH (pH u, 24 h post mortem) on the development of the pale, soft and exudative (PSE) characteristics in pig longissimus dorsi muscle were studied. Ten out of the 13 pigs used received pre-slaughter injections of adrenaline in order to deplete muscle glycogen stores. The two muscles from each pig were held at 12 or 35°C during rigor mortis development. Results from covariance analysis, using pH u as covariate, showed that a high temperature (35°C) resulted in a dramatic increase in internal light scattering (FOP) 24 h post mortem and a significant decrease in water- and salt-soluble proteins. Cooking loss, sarcomere length and drip loss did not vary significantly with rigor temperature. Interaction between temperature and pH u was estimated by assessing the relationship between pH u and the difference between the two rigor temperatures for selected traits. The best predictive model was a segmented quadratic model with a plateau which gave significant results for FOP, drip loss, water- and salt-soluble proteins. The effect of temperature decreased curvilinearly when pH increased until a constant value above which no noticeable difference was recorded (drip loss, water- and salt-soluble proteins) or a constant difference was reached (FOP). The pH values corresponding to the convergence points differed from one trait to another. They ranged from 5·72 to 6·22. These results illustrate the importance of muscle glycogen content at slaughter and subsequent pH u with regard to the development of temperature-induced PSE meat.

Electrical Stimulation of Mutton

ABSTRACTElectrically stimulated ovine muscles, restrained from shortening during rapid chilling at 0‐1 or 15‐16°C, had lower Warner‐Bratzler (WB) shear force values after 1 and 2 days aging at 0‐1°C than un‐stimulated controls, but were not significantly different at ≥4 days aging. Direct measurement of muscle fiber length showed that contraction values obtained for muscles assigned to go into rigor at 0, 15, 30 or 40°C were significantly less for stimulated muscles than for control muscles at 0°C, but of same magnitude or at rigor temperatures ≥15°C. WB shear force values indicated that, at temperatures ≥15°C, increase in tenderness due to stimulation became small after 7 days aging at 0‐1°C, whereas at 0°C aging further increased improvement due to stimulation. Results were thus consistent with electrical stimulation reducing myofibrillar shortening at rigor temperature &lt;15°C but at temperature ≥15°C stimulation had the same effect as a few days aging.