The ultra rapid chilling of pork

Pork carcasses and sides were ultra rapidly chilled in air at -30°C and 1 m/s for 4 h and compared with controls chilled in air at 0°C and 0·5 m/s for 24 h. All the required heat was removed during the 4-h process, there was a 1% saving in evaporative weight loss, the pork could be cut and packed immediately and there were no important differences in appearance and bacteriological quality. The loin from sides, but not carcasses, froze during chilling and showed a fourfold increase in drip loss. Loins from both sides and carcasses were tougher than the controls.     

The effects of spray-chilling carcasses on the shrinkage and quality of beef

After slaughter, alternate beef carcass sides (left, right) were allocated to an intermittent spray-chilling cooling treatment using water (4 cycles per hour; 60 s/cycle) and conventional air chilling (1-2°C; air velocity 0·5 m/s), or conventional air chilling only. Experiments 1, 2, and 3 (n = 19, 26 and 16 carcasses) involved spray-chilling for 4, 8, 12 h in shrouded sides, whereas experiment 4 (n = 16 carcasses) involved 8 h of spray-chilling in unshrouded sides. At 24 h post-slaughter all sides were ribbed (12 13 th ribs ), and assessed for meat and fat colour. Half the treatment and control sides in each experiment were aged for 6 days, while the boneless ribs and inside rounds were removed from the remaining sides, vacuum packaged and held for 6 days. After 6 days of storage, retail packs of rib steaks and round roasts were prepared and assessed for colour and drip losses over a 4-day period. Spray-chilling significantly reduced carcass shrinkage at 24 h post slaughter in experiments 1-4 by 0·48, 0·69, 0·89 and 1·48%, respectively. After 6 days of cooler storage, spray-chilling significantly reduced carcass shrinkage in experiments 3 and 4 only (0·47 and 0·94%). Weight and drip losses for vacuum packaged ribs and inside rounds were not influenced by spray-chilling over 6 days of storage. Spray-chilling had no influence on rate of pH decline, but reduced loin and round muscle temperatures by 1-2°C. Loin eye muscle colour and shear force were not affected by treatment, but in experiments 2, 3 and 4, fat colour was significantly lighter in spray-chilled compared to conventionally chilled sides. Colour changes and drip losses in retail packs over 4 days for rib steaks and round roasts were not related to spray-chilling. It was concluded that spray-chilling could provide a moderate reduction in carcass shrinkage during cooling without having a detrimental influence on muscle quality.     

The ultra-rapid chilling of lamb carcasses

Experiments were carried out on the effects of chilling lamb carcasses very rapidly in a pre-rigor condition. The chilling regime which was finally used was to cool the carcasses at an ambient temperature of -20°C and an air speed of 1·5 m/s for 3·5 h. Examination of striploins from carcasses subjected to this chilling regime showed that, after 7 day's storage, the meat was as tender as that from carcasses which had been conventionally chilled at 4°C for 24 h There were significant reductions in weight loss as a result of ultra rapid chilling, compared to conventionally chilled carcasses. The reductions obtained after 24 h varied between 0·8 and 0·9%, depending on whether the carcasses were washed or unwashed.     

Cryogenic chilling of pork carcasses: Effects on muscle quality, bacterial populations and palatability

Two experiments were conducted to determine the effects of cryogenic chilling on the carcass shrinkage, meat quality, bacterial condition and palatibility of pork. In experiment I, pork sides were chilled at 1°C (n = 20), or immersed in liquid nitrogen (LN) for 1 or 3 min prior to placement in a 1°C cooler. Muscle temperature in the loin was significantly lower at 2 and 6 h post mortem in treated compared to control sides, and loin muscle pH was higher (P < 0·05) at 6 h post mortem in sides immersed for 3 min in LN. Carcass side shrinkage was reduced from 29·3 g kg(-1) in control sides to 20·9 and 13·5 g kg(-1) in sides dipped in LN for 1 and 3 min. Chilling treatment had no significant effect on the survival of mesophilic bacteria on carcass sides, on meat colour, drip loss, protein solubility or sarcomere length, but sides dipped for 1 min in LN has a higher muscle shear value than control sides. In experiment II, carcass sides from halothane positive (H+) and negative (H-) pigs were conventionally chilled (n = 49), immersed in LN for 3 min (n = 23), or electrically stimulated and chilled in LN for 3 min (n = 26). Similar results for temperature, pH, colour, protein solubility and drip loss in loin muscle were found to those in experiment I. Laboratory taste panel results showed that chilling treatment had no effect on palatability. Genotype produced meaningful differences in most palatability attributes with H+ pigs having less tender, less juicy and less desirable flavour than pork from H- pigs. Laboratory studies with inoculated fresh muscle slices showed that a 3 min immersion in LN resulted in a 10-fold reduction in the aerobic spoilage pseudomonads, but effects upon other spoilage bacteria and potential human pathogens were less pronounced. It was concluded that cryogenic chilling using LN reduced carcass shrinkage during cooling, but had no consistent effects on meat quality, palatability or bacterial numbers on the carcass. In contrast, genotype had a significant effect on most pork quality and palatability attributes.     

The effects of different chilling methods on meat quality and calpain activity of pork muscle longissimus dorsi

The objective of this study was to investigate the effects of conventional chilling (0 to 4 °C), rapid chilling (RC, -20 °C for 30 min, followed by 0 to 4 °C), and short-duration chilling (0 to 4 °C for 30 min, followed by 25 °C) on meat quality and calpain activity of pork muscle longissimus dorsi (LD). The muscle quality characteristics pH, color, cooking loss, pressing loss and tenderness, and calpain activities were measured 0-, 3-, 12-, and 24-h postmortem. Results show that the RC resulted in a faster temperature decline of the muscle, and prevented the meat pH and Commission Internationale de l'Eclairage L* value from declining during postmortem aging. RC also reduced meat cooking loss and pressing loss compared with the other two chilling methods. However, the chilling methods did not significantly affect meat shear force. During the first 24-h postmortem, there was not a noticeable change in the activity of m-calpain. But μ-calpain activity decreased regardless of chilling method. In the rapidly chilled carcasses, μ-calpain activity remained the same 3- and 12-h postmortem. However, in the short-duration chilled and conventionally chilled carcasses, the activity was visibly reduced. At 24-h postmortem, no clear zones on the gel were observed in all three treatments. PRACTICAL APPLICATION: Conventional and RC methods are commonly used for pork in commercial practice nowadays. Compared with conventional chilling, the effect of RC on quality parameters of pork varies. In recent years, short-duration chilling (SC) is widely used in many Chinese pig slaughtering facilities. However, few researchers have studied the effect of SD on pork quality. Therefore, the present study investigated the effect of different chilling methods on functionalities or quality of chilled pork meat.     

The effect of pre-slaughter showering and post-slaughter rapid chilling on meat quality in intact pork sides

Thirty pairs of Landrace or Large White pigs were used to determine the effects of pre- and post-slaughter cooling treatments on pork quality and yield. One animal from each pair was showered in cold water and after slaughter one side from each carcass was rapidly chilled and the other side was conventionally chilled. Two experiments were carried out in winter: they examined different times of exposure to cooling treatments; a further experiment was carried out in summer time. Showering caused a reduction in the temperature of the deep loin at 40 min post mortem (P < 0·01). Rapid chilling caused a further reduction in carcass temperature and the rate of pH fall was lower (P < 0·05) in the rapidly chilled sides. There was a strong indication that showering in the winter time lowered drip loss in slices of Longissimus dorsi muscle (P = 0·077) whereas showering in the summer time was not effective. Shower water temperature may have been important in this regard. Showering did not lower drip loss in intact pork legs. Rapid chilling was not effective in lowering drip loss in either slices of Longissimus dorsi or intact pork legs. Rapid chilling at -20°C for 3 h without an air blast lowered evaporative chill losses in sides of pork by 27-29% (P < 0·1) compared to normal chilling. Reduced treatments gave reduced effects. Neither treatment had any significant effect on cooking loss or toughness in broiled slices of pork Longissimus dorsi muscle.     

Shrouding, Spray-chilling and Vacuum-packaged Aging Effects on Processing and Eating Quality Attributes of Beef

Sixteen beef sides were shrouded or unshrouded and then chilled using a conventional air or a water spray-chilling system. After chilling, the semitendinosus (ST) muscle was excised from each side, cut into four roasts, vacuum-packaged and aged for 3, 10, 24, or 38 days. Spray-chilling of shrouded and unshrouded sides was more effective than air chilling in lowering muscle temperature after cooling 8 hr. Unshrouded, spray-chilled sides had the least shrinkage after 24 hr. Trained panel scores and instrumental analysis of cooked roasts showed meat tenderness and juiciness were unaffected by shrouding and chilling methods; however, roasts aged 24 and 38 days were more tender than those aged 3 days.     

Electrical stimulation and ultra-rapid chilling of pork

Six pigs were stimulated at 5 min post mortem and six remained unstimulated. All the pigs were split hot and one side from each pig was rapidly chilled in two stages (air at -40°C and 1 m/s for 80 min followed by 0°C and 0·5 m/s for 130 min) and the other side was conventionally chilled (air at 0°C and 1 m/s for 24 h). The weight loss from rapidly chilled sides was approximately 1% less than that from conventionally chilled controls. Cooked samples of Longissimus dorsi were tougher from unstimulated rapidly chilled sides (0·23 J) than from unstimulated conventionally chilled sides (0·18 J), whilst samples from both stimulated treatments were significantly more tender (0·15 J). These differences in toughness are thought to be due to a combination of cold shortening and lack of conditioning. The average pH in the longissimus dorsi of both rapidly and conventionally chilled stimulated sides at 50 min post mortem was 5·57 and samples from these muscles were slightly paler and more watery than the unstimulated controls.     

The quality of pork and the shelf life of the chosen carcass elements during storage depending on the method of carcass chilling

The aim of this study was to analyze the influence of the chilling method on meat quality and the microbiological durability of pork cuts during storage. The left half‐carcasses were put through the shock tunnel and the right half‐carcasses were placed directly in the chilling room. After chilling, pH measurements were taken in two muscles. The carcasses were cut, and drip loss, marbling, and color of LL muscle were estimated. The microbiological quality of meat elements was estimated according to the procedure included in the EC regulation. The total viable count tests were done after chilling, 8, 12, 14, 16, and 18 days of storing. The drip loss was higher in the group that was chilled slower. In the group of carcasses chilled quickly lower mass losses were observed. The positive effect of ?26 °C in the shocking tunnel on the microbial quality of carcass and vacuum packed primal cuts was not as intensive as expected. As showed the above presented results of the study, the economic aspect of pork carcass chilling system first of all should be taken under consideration in meat production.

Practical applications

The study shown that very low temperatures in the shock tunnel in chilling process of the pig carcasses (e.g., ?26 °C) do not bring the expected results as a significant increase in the shelf life of meat cuts and quality of meat. Therefore, it is useful to modify the regime of temperature through the use in industrial practice of higher temperatures in the shock tunnel. The economic aspect of pork carcass chilling system first of all should be taken under consideration in choosing of the chilling method.     

Chilling pig carcasses: Effects on temperature, weight loss and ultimate meat quality

Effects of conventional (4°C, air velocity 0·5 m/s) and forced chilling at -5°C (120 min) or -30°C (30 min) with air velocities of 1, 2 or 4 m/s, followed by conventional chilling till 24 h post mortem on temperatures, meat quality and weight losses, were studied. Experiments were carried out in six batches of six slaughter pigs each (crossbred gilts, weighing 105-110 kg. The subcutaneous temperature decreased very rapidly to values below 0°C when 'ultra' rapid chilling (-30°C) at high air velocities (4 m/s was used. Immediately after rapid chilling, when the carcasses were railed into a conventional chiller, the subcutaneous temperature increased above the air temperature, after which the decline in temperature was continued. Temperature inside the biceps femoris muscle decreased from the start of chilling rather slowly according to an asymptotic curve until ultimate values of 4°C were reached. Theoretically calculated temperatures during slaughter and chilling were comparable with the measured values; indicating that a finite-element calculation method in combination with a cylindrical model for heat transport can be used to predict muscle temperatures for various chilling regimes. Losses in carcass weight, 24 h after conventional and forced chilling at -5°C, were about 2%. After 'ultra' rapid chilling (-30°C) the losses were reduced to 1·3% when air velocity was increased to 4 m/s. Meat quality of the longissimus lumborum muscle was not significantly affected by the various chilling regimes except for the variables related to tenderness. The Warner-Bratzler shear forces were higher (P < 0·05) together with shorter sarcomere lengths (P < 0·10) after 'ultra' rapid chilling at a high (4 m/s) air velocity, indicating an increased risk of cold shortening.     

冷却肉的冷却与包装

生猪宰后胴体迅速进行冷却处理,使胴体温度在24小时内降为0～4℃,并在后续的分割、包装、流通和零售等过程中,始终处于0～4℃范围内的生鲜肉称之为冷却肉.微生物污染是冷却肉产品质量的重要危害.冷却肉的流通,目前采用加工厂内真空大包装,运输到超级市场后,制作成托盘保鲜小包装.     

Effects of cryogenic chilling on beef carcass grade, shrinkage and palatability characteristics

Alternate right or left sides of 90 carcasses were randomly selected and chilled at -70°C for 5 h, held at +16°C for 4 h and held at 1°C for 15 h (rapid chill-RC). The remaining sides were chilled at -7°C for 24 h (conventional chill-CC). Physical measurements and USDA quality grade data were obtained at 24 h post mortem and palatability samples were collected at 3-5 days post mortem. RC sides had 0·9% less shrinkage (P < 0·05) at 24 h post mortem when compared to paired CC sides. Beef sides that were given the RC treatment had a darker, softer lean (P < 0·01) and received higher marbling scores (P < 0·01) at 24 h post mortem than did CC sides. Loin steaks from RC sides had longer sarcomeres, less shear resistance and higher sensory panel tenderness ratings. It may be possible to rapidly chill carcasses with less carcass shrinkage and with no detrimental effects on USDA quality grade or on beef palatability.     

Colour stability of bovine Longissimus and Psoas major muscle as affected by electrical stimulation and hot boning

From eight electrically stimulated and eight non-stimulated cows the righthand-side longissimus and psoas major muscles were hot boned within 1 1 2 h post mortem, vacuum packaged and chilled and storred at 1±1°C. Immediately after slaughter, the lefthand carcass-sides were blast-chilled for 1 1 2 h and subsequently chilled at 1±1°C until the following day. After cold boning, the longissimus and psoas major muscle were packaged, chilled and stored as the hot boned muscles. After 12 days of storage, steaks, cut from the primals, were displayed at 1±1°C under continuous illumination (300-400 lx). Colour measurements after 0, 2 and 4 days of display revealed a significant (p<0·10) effect of time of boning on non-stimulated psoas major muscle (lower values for a (?), b (?) values, chroma and %R630-%R580). Significant effects of electrical stimulation were not observed. Changes in hue tended to be more pronounced when the meat had been stimulated. Changes in chroma were largest (p<0·10) is non-stimulated, hot boned psoas muscle. Analysis of variances showed that in the longissimus muscle significant effects (p<0·10) of time boning and electrical stimulation were present. The effect of time of boning was often influenced by the use of electrical stimulation. Changes in hue and chroma indicated that hot boned samples had a higher colour stability than cold boned controls, especially when the carcasses had not been stimulated electrically. The observed differences in colour stability were rather small in all treatment groups and are not expected to present any practical merchandising problem.     

Hot cutting of goat carcasses following early post-mortem high temperature ageing

Hot cutting of goat sides into bone-in joints, such as leg, shoulder and loin, 3 h after the sides were left hanging at an ambient temperature of 34°C with (treatment II) or without (treatment I) subsequent chilling prior to freezing did not adversely affect colour of meat, tenderness, cooking loss or water-holding capacity compared with normal chilling. The latter process (treatment III) significantly (P < 0·05) increased evaporative weight loss from the sides. Differences in colour, shear force, evaporative weight loss, cooking loss, drip loss from the leg joint and water-holding capacity between treatment I, where sides were hung at room temperature for 3h, and treatment II, where sides were given an additional chilling period of 21h after hanging, were not significant. These findings indicate that, in countries with ambient temperatures above 30°C, goat sides or carcasses can be cut hot after a 3h hanging period at ambient temperature and subsequently frozen without deterioration in the quality or processing properties of the meat.     

Effect of electrical stimulation, hip suspension and ageing on quality of chilled pig meat

Carcasses from 60 Large white pigs, weighing 62-85 kg, were split and half were stimulated (700 V, 12·5 Hz for 90 s) 20 min after slaughter. Half of the stimulated (ES) and half of the non-stimulated sides were suspended from the Obturator foramen at 40 min after slaughter and resuspended from the Achilles tendon after 6 h. The sides were then subjected to one of two chilling treatments: (a) air at -15°C until M. longissimus dorsi (LD) in the lumbar region was below 10°C (approx. 3 h from slaughter), followed by air at 1°C for the remainder of chilling; (b) air at 1°C throughout. Rapid chilling increased toughness of LD but not M. semimembranosus (Sm). Stimulation improved tenderness in both muscles, increased drip loss in Sm and increased paleness in LD which could be reversed by rapid chilling. Pelvic suspension reduced drip and improved tenderness with similar magnitude to ES. Ageing improved tenderness in all except pelvic suspended sides but ES produced the most tender pork at 7 days.     

"Chilled" pork-Part I: Sensory and physico-chemical quality

Chilled meat exportation comprises chilling within 48h post-mortem to temperatures <0°C without freezing and holding under these conditions for several weeks. The effects of this ageing on sensory quality of pork are unknown and hence the objective of this study was to compare the sensory quality of Canadian pork as found in an export (Japan) market and locally. Regardless that the Japanese market's quality criteria were met, pork sorted on-line differed (P<0.05) from that for the domestic market only for lightness, exudate and cooking loss; no differences in intramuscular fat content were observed. Overall, a trained panel scored weaker pork and meat flavours and odours in the export than the domestic pork as a result of either the quality by selection if roasted or the ageing (-1.7°C, 43days exported chilled or 3.1°C, 5days domestic) if grilled or shabu shabu. Grilled pork was also more tender, sweeter and had stronger caramel flavour with the chilled ageing.     

Investigation of methods to detect mechanically recovered meat in meat products - III: Microscopy

Carcasses from 36 Large White gilts, 70–80 kg live weight, were randomly allocated to three experimental groups. Pigs in the first group were electrically stimulated with low voltage during bleeding (85v, 14Hz for 64 s) and split before cooling. The left sides were rapidly chilled in air at -15°C for 75 min and then at 1°C until 24 h post-slaughter; right sides were chilled conventionally in air at 1°C for 24 h. In the second group, two different treatments were used 20 min post-slaughter: left sides were stimulated with low voltage, and right sides with high voltage (700 v, 12·5 Hz for 90 s). Both sets of sides were chilled rapidly. Carcasses from the third group were not stimulated, and sides chilled either rapidly or conventionally. Drip loss, colour and texture were measured in M. longissimus thoracis et lumborum at 3 and 10 days post-slaughter.

At 3 days post-slaughter the high voltage, treatment gave meat which was the most tender, was not pale and lost no more drip than unstimulated controls. Low voltage stimulation during bleeding gave meat which was 18% more tender than the unstimulated controls, but the improvement in tenderness was not as great as the 28% achieved with high voltage. Unexpectedly, low voltage stimulation applied 20 min after slaughter, was almost as effective in improving tenderness (by 17%) as low voltage applied during bleeding.

Tenderness improved from 3 days to 10 days in all stimulated samples, but not in unstimulated controls. The results suggest a degree of coldtoughening in the latter, even with conventional chilling, and a positive effect of electrical stimulation on tenderness, independent of its protective action against cold-shortening.     

Physical and sensory attributes of hot-processed and conventionally chilled hams and bellies from electrically stimulated and non-stimulated pork carcasses

Forty-eight fresh hams and bellies were obtained from 24 market weight hogs (x = 94·5 kg) of which twelve were electrically stimulated (ES) by pulsing current immediately after exsanguination. The left side of each non-stimulated (NS) carcas was fabricated after conditioning for 3h post mortem at 17°C (NS hot-processed). The left sides of ES carcasses were fabricated 1 h pm. The right sides were fabricated following a 24 h cooler chill at 2°C (conventionally chilled: CP). Hams from ESCP carcasses had higher (P < 0·05) smokehouse yields than hams from NS carcasses. Hams that were hot-processed had higher smokehouse yields than the NSCP hams. Time of fabrication (1, 3 or 24h post mortem) did not affect smokehouse yields. Conventionally chilled bellies obtained from ES carcasses showed higher (P < 0·05) residual nitrite levels than those front electrically stimulated hot-processed (ESHP) carcasses. No differences were found for residual nitrite levels in the non-electrically stimulated sides. Panelists were unable to detect any sensory differences from the bacon strips. Sensory scores of ham slices were more juicy for non-stimulated hot-processed carcasses (NSHP) than those from ESHP carcasses. Panelists found the ham slices from NSCP carcasses to be more tender (P < 0·05) than those from electrically stimulated cold-processed (ESCP) carcasses. Results from this study clearly indicated that hot-processing of pork can provide hams and bellies that are acceptable for the production of cured hams and bacon of comparable quality and yield to those currently being produced under conventional processing methods.     

The chilling of carcasses

Biochemical processes and structural changes that occur in muscle during the first 24h postmortem play a great role in the ultimate quality and palatability of meat and are influenced by the chilling processes that carcasses are subjected to after slaughter. For beef and lamb, employing chilling parameters that minimize cold shortening is of greatest importance and can be best addressed by ensuring that muscle temperatures are not below 10°C before pH reaches 6.2. For pork, because of the impact of high muscle temperatures and low pH on the development of pale, soft, and exudative (PSE) pork, a more rapid chilling process is needed to reduce PSE with the recommended internal muscle temperature of 10°C at 12h and 2-4°C at 24h. Spray chilling, a system whereby chilled water is applied to carcasses during the early part of postmortem cooling, is used to control carcass shrinkage and to improve chilling rates through evaporative cooling. Delayed chilling can be used to reduce or prevent the negative effects of cold shortening; however, production constraints in high-volume facilities and food safety concerns make this method less useful in commercial settings. Electrical stimulation and alternative carcass suspension programs offer processors the opportunity to negate most or all of the effects of cold shortening while still using traditional chilling systems. Rapid or blast chilling can be an effective method to reduce the incidence of PSE in pork but extreme chilling systems may cause quality problems because of the differential between the cold temperatures on the outside of the carcass compared to the warm muscle temperatures within the carcass (i.e., muscles that are darker in color externally and lighter in color internally).     

Improving pork quality by electricalstimulation or pelvic suspension ofcarcasses

This investigation compared the separate and combined effects on meat quality of electrical stimulation (ES) and pelvic suspension of pig carcasses chilled rapidly or conventionally. Sides from 80 pigs, 80–90 kg live weight, were allocated to one of four treatments followed by either conventional chilling (1°C for 24 h) or rapid chilling (-20°C for 2–3 h, before 1°C until 24 h post-slaughter). The four treatments were: Achilles suspended, with and without high voltage ES, and pelvic suspended, with and without ES.

The quality attributes: pH, colour and opacity, drip loss, instrumental and sensory texture were measured in M. longissimus thoracis et lumborum, at 10 days post-slaughter. Rapid chilling reduced the evaporative weight loss by 0·5% There were no significant effects of treatment on colour or opacity, although ES samples were slightly paler. Drip loss was also slightly greater with ES, particularly when combined with pelvic suspension, but in no case was the meat classified as PSE. Instrumental measurements of 'texture showed improved tenderness from both ES and pelvic suspension, even after 10 days ageing. The improvement was less pronounced when ES and pelvic suspension were combined Taste panelling confirmed that samples treated by ES or pelvic suspension, separately or combined, were significantly more tender than samples from non-ES, Achilles hung sides. ES and pelvic suspension were equally effective in improving the tenderness of pork loin. Pelvic suspension did not suffer the disadvantage of increased drip loss that occurred with ES in this study.