Preslaughter resting and hot-fat trimming e ects on the incidence of pale, soft and exudative (PSE) pork and ham processing characteristics

Transcription

1 Meat Science 54 (2000) 221±229 Preslaughter resting and hot-fat trimming e ects on the incidence of pale, soft and exudative (PSE) pork and ham processing characteristics B.L. Owen a, J.L. Montgomery b, C.B. Ramsey b, M.F. Miller b, * a Excel Corporation, PO Box 910, Plainview, TX 79072, USA b Department of Animal Science and Food Technology, Texas Tech University, 1 Lubbock, TX 79409, USA Received 22 February 1999; accepted 25 June 1999 Abstract E ects of preslaughter rest (0, 1, 2 or 3 h) and hot-fat trimming (HFT, one side) on muscle quality characteristics of hams and loins were tested with 120 pigs. Center-cut loins from each carcass side were vacuum packaged and stored for 7 or 14 days at 2 C. Pigs not rested before slaughter had a skin temperature 3 C higher and ham muscle temperatures 1 C higher than pigs rested 1±3 h (P<0.05). Three hour muscle ph was highest if pigs were rested for 1 h. HFT signi cantly accelerated carcass chilling rate, but did not a ect rate of muscle ph decline. After 14 days of aging, pigs not rested had lower sensory panel ratings for juiciness, tenderness, avor and overall mouthfeel of loin chops than pigs rested 1 or 2 h. Percentage bound water of hams was highest (P<0.05) if pigs rested 1 or 2 h rather than a shorter or longer times. Pigs should be rested 1 h before slaughter and HFT carried out to allow more rapid carcass chilling and improve muscle quality. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: PSE pork; Hot-fat trimming 1. Introduction Pork muscles after adequate post-mortem chilling vary widely in color and gross morphology ( rmness and structure; Bray, 1966). Pale, soft and exudative (PSE) pork is a condition in which certain muscles are very pale, soft and watery. PSE pork is associated with a rapid rate of post-mortem glycolysis, resulting in a ph below 5.4 while the carcass is still at a high temperature (36±40 C; Briskey, 1964). Meade and Miller (1990) estimated that the US pork industry loses $32 million annually because of PSE pork. Studies in US slaughter plants have shown that PSE levels uctuate from 6 to 33%, depending on the conditions of the slaughter plant (Kau man, Cassens, Scherer & Meeker, 1992). Grandin (1989) compared the incidence of PSE in pigs rested 2.5 h before slaughter versus pigs slaughtered within * Corresponding author. Tel.: ; fax: Mention of trade names and products are necessary, but does not mean Texas Tech University warrants these products to the exclusion of other products. Texas Tech publication T address: mfmrraider@aol.com (M.F. Miller). 15 min of their arrival at the plant. Resting the pigs dramatically reduced extreme PSE from 18% in unrested pigs to 1.3% in rested pigs. Fortin (1988) reported that resting pigs for 3 h before slaughter resulted in a 27% reduction in PSE. Van der Wal, Engel and Hulsegge (1997) accounted improved pork quality of rested pigs to lower muscle temperature and increased ultimate ph. Rapid chilling of pork carcasses may be an e ective means of reducing PSE pork, but increases the refrigeration requirements. Meade and Miller (1990) concluded that a 7 C reduction in internal ham temperature at 3 h post-mortem, resulting from hot-fat trimming (HFT), reduced incidence of PSE pork by 30%. Frederick, Miller, Jones, Meade and Ramsey (1994) reported internal ham temperatures at 2 h post-mortem from HFT carcass sides were about 3 C lower than control (not fat trimmed, NFT) sides. While some authors such as Milligan, Ramsey, Miller, Kaster and Thompson (1998) have looked at the e ects of resting and HFT on the incidence of PSE pork, none have researched the combination of HFT and resting for 0, 1, 2 and 3 h under spray chilling conditions using pigs from a wide genetic source. Thus, the objectives of /99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S (99)

2 222 B.L. Owen et al. / Meat Science 54 (2000) 221±229 this study were to determine the e ects of resting pigs before slaughter and a faster carcass chill rate (produced by HFT) on muscle quality characteristics in hams and loins from pigs from a wide genetic source. Also, the processing characteristics, sensory attributes, and texture parameters of boneless, smoked/cured hams from HFT and di erently rested pigs were determined. 2. Materials and methods 2.1. Selection and slaughter Forty pigs were selected each day for 3 days (to ensure genetic variability) and slaughtered by standard US industry procedures. Ten pigs per day were randomly selected for a preslaughter group that was unloaded from the truck, continuously moved and then slaughtered within 15 min of arrival. The remaining pigs were divided into three groups of 30 pigs each (10 per day) and allowed to rest 1, 2 or 3 h before slaughter. All pigs were held under water misters and had ad libitum access to water. Immediately before stunning, the skin temperature of the neck of each hog was determined using an Omega OS51 Noncontact Thermometer (Omega Engineering Inc., Stamford, CT). Re ectance values were obtained using a Fat-O-Meter (model 87, American Tech, Inc., Dubuque, IA). Immediately after entering the chill cooler, alternating right and left carcass sides were hot-fat trimmed. During this process, the skin and all fat in excess of 6 mm were removed from the ham and loin. The other carcass side was not hot-fat trimmed. All carcasses were spray chilled for 24 h Temperature and ph decline Temperature decline was monitored hourly for 4 h (beginning at 0.5 h after stunning), and at 24.5 h postmortem. Decline in muscle ph was monitored once per hour for the rst 4.5 h and at 24.5 h post-mortem. Temperature was measured with a Taylor Model 9865 Pocket Thermometer with a 10-cm stem (Taylor Co., Lawrenceville, GA) and the ph was monitored using an Orion Model 601 Digital Ionalyzer (Orion Research, Inc., Cambridge, MA) with a puncture electrode. Temperatures were taken at the center of the ham near the femur and ph measurements were in the M. longissimus muscle at the 10th and 11th rib interface (probes were removed and re-inserted hourly) Sample collection and color evaluation After 24 h chilling, the carcasses were fabricated into wholesale cuts. Loins were cut into boneless, center-cut loins (IMPS No. 412B). Color was evaluated 15 min after bloom instrumentally on the loins at the 10th rib for L*, a* and b* values, using a Minolta Chroma Meter model CR-200b (Illuminant D 65 was used with a 1 cm diameter aperature), and subjectively, by visual appraisal by three personnel. Color, texture and rmness were scored on a 5-point scale with 5=very dark, ne and rm; 3=reddish pink, moderately ne and moderately rm; and 1=very pale, coarse and soft, respectively (National Pork Producers Council, 1991). The inside ham muscle, semimembranosus (SM) was excised and color also was determined with the Minolta Chroma Meter before they were visually scored for ham face quality and color, texture, rmness on the 5-point scale. The SM muscle near the femur was evaluated for color and colorimeter values. Loin and ham muscles were stored for 7 days at 2 C. Each loin then was halved with one-half vacuum packaged and aged an additional 7 days (14 days total). The remaining portion of the loin was visually evaluated for color, texture and rmness, and color again was instrumentally measured using the colorimeter. The loins then were cut into 2.5-cm-thick chops and frozen at 40 C until sensory panel evaluations and Warner-Bratzler shear (WBS) force values were determined. SM were frozen at 7 days postmortem Shear force and sensory evaluation of loin samples Sets of 10 samples were randomly selected from the 30 loins in each treatment for sensory panel evaluation and WBS force determination. All chops were thawed to 2 C. Two chops from each loin were broiled on a Farberware Open Hearth electric broiler (Model 450n, Kidde, Inc., Bronx, NY) to an internal temperature of 40 C and turned. All chops were removed at 70 C and temperature was monitored with a digital meat thermometer (Taylor, model 9865). Muscle from one cooked chop was cut into cm pieces for sensory evaluation. Samples were served warm to a 7-member panel selected and trained according to Cross, Moen and Stan eld (1978). Panelists evaluated each sample on an 8-point scale for juiciness, tenderness, avor intensity, avor and overall mouthfeel (8=extremely juicy, tender, intense, and characteristic pork mouthfeel; 1=extremely dry, tough, bland, unsavory, and nonpork characteristics mouthfeel, respectively). The samples were served under red lights to mask color di erences. The panelists received water and apple juice to rinse their palates between samples. The other cooked loin chop was placed on a plastic tray covered with polyvinyl chloride lm and chilled for 24 h at 2 C before WBS force determination. Three 1.27-cm-diameter cores were removed parallel to the muscle ber orientation from each of the chilled chops after being held at room temperature for 3 h. Each core was sheared once through the center with a Salter WBS device (model , Manhattan, KS).

3 B.L. Owen et al. / Meat Science 54 (2000) 221± Boneless ham production The HM were thawed for 2 days at 2 C, trimmed of all surface fat and connective tissues, and ground through a three-hole kidney plate with 46-cm ori ces and weighed. Each HM was placed in a vacuum bag with a brine solution that contained 1 g of sodium erythrobate, 3.5 g of curing solution [salt (91.75%), sodium nitrite (6.25%), F, D and C red No. 3 ( %), and less than 2% sodium silicon aluminate and propylene glycol; A.C. Legg Co., Birmingham, AL], 9 g of phosphate, 19 g of dextrose, 32.5 g of salt and 127 g of water. The bags were sealed, and the HM were tumbled in a Lance massage tumbler (model LT5, Lance Ind., Allenton, WI) for 1 h and then placed in a chill cooler at 2 C overnight. HM were re-tumbled for 20 min and stu ed into 6.4-cm-diameter brous casings using a table top stu er (model D-7300, F. Dick Co., Esslingen, Germany) with a 3-cm lling tube. Following stu ng, hams were weighed to determine a precooked ham weight and cooked to an internal temperature of 65 C in a Vortron Processing Oven (model 2500, Vortron, Inc., Beloit, WI) using a three-cycle processing cycle: (1) 0.5 h at wet bulb (WB) 42 C and dry bulb (db) at 54 C, (2) 2 h at 53 CWBand66 C db with smoke and, (3) 63 C WB and 77 C db with smoke until the internal temperature of hams reached 66 C. Hams were chilled at 2 C for 24 h and reweighed to determine the cooked/chilled weight Ham yield determination Cooked ham yields were determined: Cooked yield, %=(cooked and chilled weight/raw weight)100. Sliceability (percentage of broken slices) was determined by cutting a 5-cm-thick section from each ham and slicing the section into as many 0.5-cm-thick slices as possible using a Berkel electric meat slicer (Berkel Inc., LaPorte, IN). Sliceability was calculated: Broken slices, %=100 (number of broken slices/total number of slices)100. Percentage free water was determined by the Carver Press Method (Ockerman, 1981). Percentage free water was calculated: free water, %=[expressed water area of meat61.1/total percentage moisture of meat sample] Shear force and sensory evaluation of ham samples Sets of 10 samples were randomly selected from each treatment for sensory panel evaluation and Warner- Bratzler Shear force (WBS) determination, as explained above. Panelists evaluated each sample on an 8-point scale for juiciness, tenderness, avor intensity, ham avor and overall ham mouthfeel (8=extremely juicy, tender, intense, tasty and ham mouthfeel; 1=extremely dry, tough, bland, unsavory and non-ham mouthfeel). The samples were served under red lights to mask any color di erences. To obtain WBS values, four 1.3-cmdiameter cores were removed from a 2.5-cm-thick ham slice parallel to the muscle ber orientation Objective texture parameters Ham cores (as described above) were compressed twice to 70% of their original height with an Instron 1132 Universal Testing Machine (Instron Corp., Canton, MA). Full scale load was set at 20 kg, chart paper at 20 mm/min and the crosshead speed at 50 mm/min. Hardness, springiness, cohesiveness and chewiness were determined according to Bourne (1978) Proximate analyses Ham slices were trimmed of rind and then ground using a Robot Coupe food processor (model R800, Robot Coupe Inc., Ridgeland, MS) for subsequent moisture, fat, ash and protein analyses according to the Association of O cial Analytical Chemists (AOAC, 1990) procedures Statistical analyses Data were analyzed using the Statistical Analysis System Package (SAS, 1990). Carcass characteristics were analyzed by the GLM package for a 2 (fat trim)2 (aging period)4 (rest period) factorial design (Steel & Torrie, 1980). Ham measurements were analyzed by Proc GLM Procedures for a 2 (fat trim)4 (rest period) factorial design (Steel & Torrie). No signi cant interactions were detected at P<0.05. Least squares means were separated by the protected Probability of Di erence method with an level of 5%. 3. Results and discussion 3.1. Skin and carcass temperature E ects of preslaughter rest period on skin temperature immediately before slaughter are presented in Table 1. Rested pigs had a skin temperature 3 C lower after 1 h than pigs not rested before slaughter. Presumably, skin temperatures are typically lower than core body temperatures of 37 C. These data show no advantage in lowering skin temperatures would be gained by resting pigs longer than 1 h. Santos, Almeida, Matias, Fraqueza, Roseiro and Sardina (1997) also found resting pigs 2±3 h slightly reduced skin temperature. Gariepy, Amiot and Nadai (1989) measured the skin temperature of pigs by infrared thermography and successfully detected the meat quality problem (PSE or DFD) antemortem. In our

4 224 B.L. Owen et al. / Meat Science 54 (2000) 221±229 Table 1 Least squares means and SEM for live pig skin temperatures and carcass traits by rest period a Rest period (h) Trait SEM Skin temperature ( C) 32.2a 29.3b 29.1b 28.9b 0.44 Carcass trait c Re ectance value a,b Means in a row bearing unlike letters are di erent (P<0.05). c Carcass traits were determined with a Fat-O-Meter at Monfort, Inc. experiments re ectance values were not di erent (P>0.05) among resting treatments. Average ham temperature at 0.5 h post-mortem when the carcasses entered the chill cooler was 1 C higher (P<0.05) for pigs not rested before slaughter than for those allowed to rest (Table 2). At 1.5 h post-mortem, pigs not rested had ham temperatures 1±2 C higher (P<0.05) than rested pigs and pigs rested 2 h before slaughter had the lowest ham temperatures. At 2.5 h post-mortem no signi cant di erences were found between pigs rested 0 and 1 h, while pigs rested 2 and 3 h were signi cantly di erent. At 3.5 and 4.5 h postmortem no signi cant di erences were found for ham temperatures of pigs from any rest period. Therefore, resting pigs 2 h before slaughter would have the greatest e ect on decreasing ham temperatures during the rst 2 h post-mortem. The rst 2 h post-mortem is a crucial time when PSE development would be greatest due to increased proteolysis and rate of ph decline (Briskey, 1964; Tabilo, Flores, Fiszman & Toldra, 1999). However, at 24.5 h post-mortem pigs not rested had the lowest ham temperatures (P<0.05). Although signi cant di erences existed between rest periods at these times, these di erences would have little or no e ect on the incidence of PSE because protein degradation and resulting decreases in muscle quality occurs during the rst 2±4 h post-mortem (Judge, 1969). HFT accelerated ham chilling rate 1±3 C/h for the rst 4 h of chilling. HFT resulted in lower ham temperatures (P<0.05) for all times measured after the carcasses were placed in the cooler at 0.5 h post-mortem. The results for carcass chilling agree with Frederick et al. (1994) who reported a decrease in internal ham temperatures (P<0.05) between HFT and NFT sides of stressed and unstressed pigs up to 4 h post-mortem. However, unlike the current study, they found no signi cant di erences after 4 h chilling Muscle ph HFT did not a ect the ph decline of the M. longissimus muscle. However, resting the pigs before slaughter a ected the rate of ph decline at all times measured. At 0.5, 1.5, 2.5 and 3.5 h post-mortem, loin muscles from pigs rested 1 h had a higher (P<0.0001) ph than pigs not rested or rested longer. At 24.5 h postmortem, pigs rested for 3 h had lower (P<0.0001) ph values than other pigs. These results indicate resting pigs 1 h before slaughter produced a higher initial muscle ph than not resting or resting longer, and pigs rested 1 h before slaughter maintained a higher ph during the crucial early post-mortem period of rigor development. Santos et al. (1997) also found resting hogs 2±3 h prior to slaughter increased ultimate muscle ph. Results from the present study indicate the impact of low ph and high temperature would be o set by HFT. Resting pigs Table 2 Least squares means and SEM for post-mortem temperature of hams and ph decline of loin muscles by rest period and hot-fat trimming a Trait and time post-mortem Rest period (h) SEM Yes No SEM Ham temperature ( C) 0.5 h 41.9a 40.9b 40.8b 40.9b h 39.8a 38.6b 36.9c 38.7b b 38.8a h 34.6a 34.0a 31.9c 33.0b b 34.2a h 28.8a 29.0a 28.0a 28.2a b 29.7a h 24.3a 24.2a 23.2a 24.2a b 25.4a h 2.8a 3.3b 3.7bc 3.8c b 3.8a 0.19 Loin ph 0.5 h 6.06a 6.29b 6.11a 6.16a h 5.83a 6.09b 5.84a 5.73a h 5.72a 5.89b 5.72a 5.54c h 5.72a 5.81b 5.60c 5.52c h 5.71a 5.69ab 5.61b 5.45c h 5.54a 5.60a 5.56a 5.43b a,b,c Means in a row within main e ects bearing unlike letters are di erent (P<0.05).

5 B.L. Owen et al. / Meat Science 54 (2000) 221± h before slaughter would also allow a slower ph decline during the crucial hours of early rigor development. The extended resting of pigs may be detrimental to pork quality as a result of the observed ghting during the establishment of a new pecking order in pigs that are mixed Muscle quality characteristics HFT and the resulting faster chilling rate had no e ect (P<0.05) on the CIE L*, a* orb* values of M. longissimus or SM muscles at any cooler aging time (Table 3). However, loins from pigs not rested before slaughter had higher (P<0.006) L* (lightness), a* (red), and b* (yellow) values at 24.5 h (1 day) post-mortem than pigs rested 1, 2 or 3 h. No signi cant di erences in L*, a*, b* values of loin muscles were found among the rested pigs. For loins aged 7 and 14 days, no signi cant di erences were found in CIE color values among rest periods. Resting pigs 1 h before slaughter created lower L* values (darker), which can be correlated to PSE intensity utilizing the relationship developed by Oscar Mayer Co. (Borchert, 1990). The higher L* values for pigs not rested in the present study agrees with the ndings of Grandin et al. (1989) and Fortin (1988). For inside ham muscles, pigs not rested and pigs rested 3 h before slaughter had higher L* values than pigs rested 1 or 2 h before slaughter. L* values for pigs rested 1 or 2 h before slaughter were lower (P<0.05) than for pigs rested 3 h, but were not signi cantly di erent from pigs not rested. Inside ham muscles from pigs rested 3 h before slaughter had higher (P<0.05) CIE b* values (more yellow) than pigs not rested or those rested 1 or 2 h. The high b* values in the 3 h rested hams may be a re ection of the increased ph values at 24.5 h postmortem. CIE L* values and Wisconsin color scores were used to determine the e ects of preslaughter resting and NFT on the incidence of PSE hams (Borchert, 1990, Table 3; NPPC, 1991). Pigs rested 1 h before slaughter had the lowest occurrence of PSE muscle while pigs rested 3 h had the highest incidence of PSE muscle. These results suggest pigs should be rested 1 h before slaughter to allow a higher percentage of pigs to achieve lower body temperatures before slaughter and reduce percentage of PSE muscle by about 10%. These results may vary greatly depending upon the time of year and ambient temperatures. This study was conducted during the summer, when ambient temperatures were high. Further investigation on the e ects of time of year and length of rest period before slaughter on ultimate muscle quality would help determine the best rest period as ambient temperatures vary Loin palatability Rest period did not a ect any sensory attribute for loin chops aged 7 days. After loins were aged 14 days, initial and sustained juiciness, initial and sustained tenderness, avor and overall mouthfeel were lower (P<0.05) for loin chops from pigs not rested than for pigs rested 1 h (Table 4). All of these traits except sustained tenderness and avor also were lower (P<0.05) if the pigs were not rested compared to resting 2 h. Flavor intensity and WBS values were not a ected by the resting period (P>0.05). These data suggest the combination of resting pigs 1 or 2 h before slaughter and 14 days aging produces a more juicy, tender, avorful loin chop with a higher overall mouthfeel rating than other treatment combinations. For loins aged 14 days, HFT sides had lower (P<0.05) avor intensity ratings than NFT sides although the di erence was small. Overall, resting 1±2 h and HFT had no detrimental e ects on pork sensory attributes. No detrimental e ects were shown on pork tenderness ratings. Results from research on sensory attributes of loin chops from Table 3 Least squares means and SEM for CIE color values of loins after 1, 7 and 14 days post-mortem and inside ham muscles at 1 day post-mortem by rest period and hot-fat trimming a Trait and day post-mortem Rest period (h) SEM Yes No SEM Loin, 1 day L* 48.9a 46.0b 47.0b 47.2b a* 9.4a 7.8b 8.0b 8.2b b* 4.5a 3.0b 3.6b 3.7b Ham, 1 day L* 46.0ab 43.6b 45.0b 48.5a a* b* 3.8a 3.6a 3.6a 4.9b Percentage PSE c 26%a 17%b 19%b 27%a 35% 41% a,b Means in a row within main e ect bearing unlike letters are di erent (P<0.05). c % PSE is gured using L* values and Wisconsin color scores (Borchert, 1990; NPPC, 1991).

6 226 B.L. Owen et al. / Meat Science 54 (2000) 221±229 PSE versus normal chops have been con icting. Sayre, Keirnat and Briskey (1964) reported that PSE muscles had lower juiciness and tenderness scores than normal muscles. Butcher and Zeuthen (1971), Kemp, Montgomery and Fox (1976), and Topel, Miller, Berger, Rust, Parrish and Ono (1976) found PSE pork scored lower than normal pork in juiciness, tenderness, avor and overall satisfaction. As is the case with sensory evaluation, no accord is found about the e ects of the PSE condition on WBS values among researchers. Searcy, Harrison and Anderson (1969), Merkel (1971), and Kemp et al. (1976) all reported PSE pork had lower shear values than normal pork while Butcher and Zeuthen (1971) reported the reverse Ham yield and processing characteristics Resting pigs 1 h before slaughter resulted in a lower (P<0.05) percentage of free water expression by ham slices when compared to not resting or resting pings 3 h (Table 5). HFT of carcass sides did not a ect expression of free water. In contrast to our ndings Ramsey, Hamman and Miller (1995) found HFT lowered the percentage of free water in pork muscle. The lower free water suggests hams from pigs rested 1 h before slaughter had an increased bind between ham pieces than in hams from pigs rested for a shorter or longer time. Hams from pigs rested 1 h had the lowest incidence of PSE, which may explain the changes in free water. Fox, Moody, Kemp and Henning (1970) reported that high quality hams bound (P<0.01) more water than hams of medium or low quality. Cooking loss also was not a ected by any treatment. Our observations are in agreement with Dalrymple and Kelly (1966) who also found that PSE and normal hams did not di er in cooking loss, but di er from the conclusions of Jeremiah and Wilson (1987) and Merkel (1971). No di erences were noted across treatments for WBS values of hams. Previous research on WBS values of hams made from di ering (PSE vs normal) quality groups is con icting. Kemp et al. (1971) and Fox et al. (1970) reported WBS values of hams made from PSE semimembranosus muscles were lower (P<0.05) than of hams made from high quality semimembranosus muscles. In our study, cooking loss during smoking and cooking was not a ected by any treatment. While percentage free water expression was e ected by resting, an explanation for cooking loss not being di erent does not exist Sensory evaluation Treatments did not a ect juiciness of the hams (P>0.05). Initial and sustained tenderness scores of hams were higher (P<0.05) if pigs were not rested or were rested 3 h before slaughter than if pigs were rested 1 or 2 h. The increased water bind resulting from resting may be responsible for this e ect. Ham avor ratings were higher (P<0.05) if pigs were rested 2 or 3 h before slaughter than if pigs were rested for a shorter time. Overall ham mouthfeel ratings were higher (P<0.05) if pigs were rested for 2 or 3 h (P<0.05) than 1 h. The lower tenderness ratings for pigs rested 1 h before slaughter may be explained by a greater resistance to chewing produced by a greater bind between ham pieces and lower proteolysis (Tabilo et al., 1999). Cross, Smith and Carpenter (1971) found cured hams from normal (gross morphology) semimembranosus muscles had lower (P<0.05) tenderness ratings than hams produced from PSE or DFD semimembranosus muscles. Hot-fat trimming of carcasses a ected only sustained tenderness Table 4 Least squares means and SEM for sensory measures and Warner±Bratzler shear values of loin chops aged 14 days by rest period and hot-fat trimming Trait and day post-mortem Rest period (h) f SEM Yes No SEM Loin, 14 days Initial juiciness a 5.3g 5.7f 5.6f 5.5fg Sustained juiciness a 5.1g 5.5f 5.4f 5.3fg Initial tenderness b 5.8g 6.2f 6.1f 6.0fg Sustained tenderness b 5.7g 6.2f 6.0fg 5.9fg Flavor intensity c g 6.2f 0.05 Flavor d 5.7h 6.1f 6.0fg 5.8gh Overall mouthfeel e 5.3g 5.8f 5.7f 5.5fg WBS (kg) a 5=slightly juicy. b 6=moderately tender, 5=slightly tender. c 6=moderately intense. d 6=moderately tasty, 5=slightly tasty. e 5=slightly characteristic pork mouthfeel. f,g,h Means in a row within main e ects bearing unlike letters are di erent (P<0.05).

7 B.L. Owen et al. / Meat Science 54 (2000) 221± Table 5 Least squares means and SEM for processing and sensory characteristics of ham slices by rest period and hot-fat trimming Rest period (h) j Trait SEM Yes No SEM Free water (%) a 23.7j 21.1k 22.9jk 25.1j Broken slices (%) b WBS (kg) Cooking loss (%) c Sensory traits Initial juiciness d Sustained juiciness d Initial tenderness e 6.5j 6.0k 6.1k 6.5j Sustained tenderness e 6.6j 6.2k 6.3k 6.7j k 6.6j 0.07 Flavor intensity f Ham avor g 6.0k 5.9k 6.4j 6.4j Saltiness h Ham mouthfeel i 5.9jk 5.8k 6.1j 6.2j a Calculated by: expressed water area of meat61.1/total moisture100. b Calculated by: number of broken slices/total number of slices100. c Calculated by: 100 (cooked and chilled weight/uncooked weight)100. d 5=slightly juicy, 6=moderately juicy. e 6=moderately tender, 7=very tender. f 6=moderately intense, 7=very intense. g 5=slightly tasty; 6=moderately tasty. h 5=slightly salty, 6=moderately salty. i 5=slight ham mouthfeel, 6=moderate ham mouthfeel. j,k Means in a row within main e ects with unlike letters di er (P<0.05). Table 6 Least squares means and SEM for objective texture parameters and proximate analyses of cooked hams by rest period and hot-fat trimming Rest period (h) b Trait SEM Yes No SEM Instron analyses Cohesiveness Hardness (kg) Springiness (cm) 0.63c 0.68b 0.66bc 0.66bc Chewiness a Proximate composition (%) Ash Ether extract Moisture Protein a Chewiness=cohesivenesshardnessspringiness. b,c Means in a row within main e ects with unlike letters di er (P<0.05). scores, which were lower (P<0.05) if the sides were HFT Objective texture parameters and proximate analyses Cohesiveness, hardness, and chewiness (Table 6) were not a ected by treatments, but springiness values were slightly higher (P<0.05) for pigs rested 1 h before slaughter than for pigs not rested before slaughter. Springiness (originally called elasticity) is de ned as the height that the samples recover during the time that elapses between the end of the rst bite and the start of the second bite (Bourne, 1978). The increased binding between ham pieces for pigs rested 1 h before slaughter may have resulted in a ham cores with greater resistance to change or elasticity. Ash, ether extract, moisture and protein contents of the cooked and smoked hams were not a ected by either rest period of the pigs or HFT of the carcasses (P>0.05).

8 228 B.L. Owen et al. / Meat Science 54 (2000) 221± Conclusions Results from this study indicate that pigs should be rested 1 h before being slaughtered. This rest period allowed live skin temperatures to decline, which resulted in a lower ham temperature post-mortem, improved loin and ham muscle scores, provided a slower ph decline, improved palatability of loin chops aged 14 days, and reduced free water in cooked hams. Resting pigs for a longer time resulted in no improvements in pork quality and would require a greater increase in the pen space required for resting pigs before slaughter at the pork packing facility. This rest period resulted in higher binding between ham pieces, which produced a lower percentage free water and ham muscles that were more springy. Hot-fat trimming resulted in lower sensory panel ratings for sustained tenderness, indicating an increase in binding between muscle pieces. Hot-fat trimming had no e ect on any other attribute measured. HFT increased chilling rate and would enable pork carcasses to be rapidly chilled in the same facilities without the expense of adding additional refrigeration and would allow packers to continue to use the same equipment. Packers could actually reduce the refrigeration demands because less total carcass mass and heat units would require chilling. HFT results in faster temperature declines and reduces the chance for increased protein denaturation at low ph's early postmortem. Thus, in combining the utilization of a 1 h rest and HFT the costs of increased pen space for the 1 h resting should be o set by the savings in refrigeration and trimming due to HFT. The study demonstrates improved pork quality can be gained by the pork industry by implementing a 1 h rest prior to slaughter and hot fat trimming. References Association of O cial Analytical Chemists (1990). O cial methods of analysis (15 ed.). Arlington, VA: Association of O cial Analytical Chemists. Borchert, L. L. (1990). Personal Communication. Director, Research and Development. Oscar Mayer Co. Madison, WI. Bourne, M. C. (1978). Texture pro le analysis. Food Technology, 32, 62±66. Bray, R. W. (1966). Pork quality Ð de nition, characteristics and signi cance. Journal of Animal Science, 25, 839±842. Briskey, E. J. (1964). Etiological status and associated studies of pale, soft, exudative porcine musculature. Advanced Food Resources, 13, 89±178. Butcher, L., & Zeuthen, P. (1971). The e ect of aging on the organoleptic qualities of PSE and normal pork loins. In Proceedings of the 2nd International Symposium on Condition Meat Quality Pigs (p. 247). Pudoc, Wageningen, Netherlands. Cross, H. R., Moen, R., & Stan eld, M. (1978). Training and testing of judges for sensory analysis of meat quality. Food Technology, 32, 48±52. Cross, H. R., Smith, G. C., & Carpenter, Z. L. (1971). E ect of quality attributes upon processing and palatability characteristics of commercially cured hams. Journal of Food Science, 36, 982±986. Dalrymple, R. H., & Kelly, R. F. (1966). Processing, composition, and organoleptic characteristics of normal and pale, soft, exudative pork. Journal of Animal Science, 25, 883(Abstr. 27). Fortin, A. (1988). The e ects of resting time on PSE in pork loins from hogs transported for two hours. Animal Research Institute, Agriculture, Canada. Ottawa. Fox, J. D., Moody, W. G., Kemp, J. D., & Henning, W. (1970). Physical, chemical and histological properties of low, medium and high quality hams at various intervals during curing and aging. Journal of Animal Science, 31, 323±326. Frederick, T. L., Miller, M. F., Jones, D. K., Meade, M. K., & Ramsey, C. B. (1994). Hot-fat trimming of pork carcasses to reduce pale, soft and exudative pork. Journal of Muscle Foods, 5, 165±173. Gariepy, C., Amiot, J., & Nadai, S. (1989). Ante-mortem detection of PSE and DFD by infrared thermography of pigs before stunning. Meat Science, 25, 37±41. Grandin, T. (1989). The e ect of rest time on PSE in pork carcasses. Final Report to Monfort, Inc., Greely, CO. Jeremiah, L. E., & Wilson, R. (1987). The e ects of PSE/DFD conditions and frozen storage upon the processing yields of pork cuts. Canadian Institute of Food Science and Technology, 20, 25±30. Judge, M. D. (1969). Environmental stress and meat quality. Journal of Animal Science, 28, 755±760. Kau man, R. G., Cassens, R. G., Scherer, A., & Meeker, D. L. (1992). Variations in pork quality. National Pork Producers Council, Des Moines, IA. Kemp, J. D., Montgomery, R. E., & Fox, J. D. (1976). Chemical, palatability and cooking characteristics of normal and low quality pork loins as a ected by freezer storage. Journal of Food Science, 41, 1±3. Kemp, J. D., Fox, J. D., Moody, W. G., & Crouse, J. D. (1971). Relationship of fresh ham traits to cured ham quality. Journal of Animal Science, 33, 362±365. Milligan, S. D., Ramsey, C. B., Miller, M. F., Kaster, C. S., & Thompson, L. D. (1998). Resting of pigs and hot-fat trimming and accelerated chilling of carcasses to improve pork quality. Journal of Animal Science, 76, 74±86. Meade, M. K., & Miller, M. F. (1990). The use of rapid chilling to reduce pale, soft and exudative pork from highly stressed hogs. Journal of Animal Science, 68(Suppl. 1), 351(Abstr. 293). Merkel, R. A. (1971). Processing and organoleptic properties of normal and PSE porcine muscle. In Procedings 2nd International Symposium Condition Meat Quality Pigs (p. 261). Pudoc, Wageningen, Netherlands. National Pork Producers Council (1991). Procedures to evaluate market hogs (3rd ed.). IA: Des Moines. Ockerman, H. W. (1981). Quality control of post-mortem tissue (Vol. 1, 10th ed.). Wooster, OH: The Ohio Agriculture Research and Development Center. Ramsey, C. B., Hamman, L. L., & Miller, M. F. (1995). Vitamin/ mineral nutritional modulation, stress and hot/fat trimming e ects on quality of pork from pigs monomutant for the PSE gene. Journal of Animal Science, 73(Suppl. 1), 160(Abstr. 203). SAS (1990). SAS User's Guide: Statistics. Cary, NC: SAS Institute. Santos, C., Almeida, J. M., Matias, E. C., Fraqueza, M. J., Roseiro, C., & Sardina, L. (1997). In uence of lairage environmental conditions and resting time on meat quality in pigs. Meat Science, 45, 253±262. Sayre, R. N., Keirnat, B., & Briskey, E. J. (1964). Processing characteristics of porcine muscle related to ph and temperature during rigor mortis development and to gross morphology 24 h post-mortem. Journal of Food Science, 29, 175±181. Searcy, D. J., Harrison, D. L., & Anderson, L. L. (1969). Palatability and selected related characteristics of three types of roasted porcine muscle. Journal of Food Science, 34, 486±489.

9 B.L. Owen et al. / Meat Science 54 (2000) 221± Steele, R. G. D., & Torrie, J. H. (1980). Principles and procedures of statistics: a biometrical approach (2nd ed.). New York: McGraw- Hill. Tabilo, G., Flores, M., Fiszman, S. M., & Toldra, F. (1999). Postmortem meat quality and sex a ect textural properties and protein breakdown of dry-cured hams. Meat Science, 51, 255±260. Topel, D. G., Miller, J. A., Berger, P. J., Rust, R. E., Parrish, F. C. Jr., & Ono, K. (1976). Palatability and visual acceptance of dark, normal and pale colored porcine M. longissimus. Journal of Food Science, 41, 628±630. Wal, P. G., van der Engel, B., & Hulsegge, B. (1997). Causes for variation in pork quality. Meat Science, 46, 319±327.