Introduction
Chilling is a critical postmortem process that influences both food safety and key meat quality traits. Historically, extreme chilling rates have been linked to quality defects, such as cold shortening from rapid temperature decline and pale, soft, and exudative pork resulting from delayed chilling (Bendall, 1973; Dransfield & Lockyer, 1985). Although such defects are now relatively rare in modern commercial processing, recent studies have demonstrated that even modest differences in postmortem chilling rate can affect meat quality. Carcass weight has been reported to influence the chilling rate of the ham and loin primals (Overholt et al., 2019; Price et al., 2022). Specifically, Price et al. (2022) reported that heavier carcasses (130 kg) chilled more slowly than lighter carcasses (104–122 kg), resulting in improved instrumental and sensory tenderness of loin chops. Given that pork carcass weights have increased by approximately 0.6 kg/year over the past 28 years, reaching a current industry average of 97 kg (USDA NASS, 2023), there is increasing concern about how heavier carcasses may affect chilling rates and meat quality. Additionally, chilling rate varies by carcass primal location, with hams generally chilling more slowly than loins (Arkfeld et al., 2016). However, these findings were derived from studies conducted in commercial plants equipped with blast chillers. Accordingly, it was anticipated that carcasses in the present study would exhibit slower temperature decline due to increased carcass weight and the limited chilling capacity of a conventional system in a non-commercial slaughter facility.
Whereas previous studies have focused on carcass weight or carcass primal location independently, this study aimed to evaluate their interactive effects on chilling rate and meat quality. This study also extends prior work by characterizing meat quality traits in select shoulder (serratus ventralis [SV] and triceps brachii [TB]) and ham (semimembranosus [SM] and semitendinosus [ST]) muscles. As carcass and primal weights increase, these muscles may offer potential as novel fresh chop candidates due to their increasing size and value (Metz et al. 2024). Therefore, the objective was to determine the effects of carcass weight and carcass primal location on postmortem muscle temperature decline and its relationship with pork quality traits.
Materials and Methods
All animal care and use procedures were approved by the Institutional Animal Care and Use Committee at the University of Illinois (Protocol # 23045) and followed standard practices described in the Guide for the Care and Use of Agricultural Animals in Research and Teaching (American Society of Animal Science [ASAS], 2020).
Pig background
The full experimental design used in this study is described in detail by Metz et al. (2024). Barrows and gilts were housed in the grower-finisher barn at the University of Illinois Swine Research Center (Champaign, IL, USA). Pigs, from 3 different commercial sire lines representative of modern swine genetics, were allocated into same-sex pens of 4 at approximately 10 wks of age based on the sire line, sex, and weights at day 0. Diets contained no dried distillers’ grains and were formulated to meet or exceed nutrient requirements for growing-finishing pigs (NRC, 2012). All pigs were between 24 and 29 wks of age at the time of slaughter. Whole carcasses (N = 71) were categorized based on hot carcass weight (HCW): Average (99–109 kg), Heavy (116–126 kg), and Very Heavy (134–144 kg). Carcass weight categories were defined to target commercially relevant distributions (USDA NASS, 2023). Both sexes and all 3 sire lines were represented in each weight category (Metz et al., 2024).
Slaughter and temperature measurement
Pigs were transported to the University of Illinois Meat Science Laboratory (Urbana, IL, USA) on 8 separate d over 8 wks. Pigs were held in lairage for a minimum of 16 h with free access to water but no access to feed. Ending live weight was recorded immediately before slaughter using a GSE Model 350 scale (GSE Scale Systems, Novi, MI, USA). All pigs were immobilized with electrical stunning and terminated through exsanguination under the supervision of the United States Department of Agriculture’s Food Safety and Inspection Service. Carcasses were split into left and right sides. Temperature loggers (Thermochron iButton Device, model DS1921G, range: −40°C to 85°C, Maxim Integrated, San Jose, CA, USA) were placed a minimum of 4.8-cm deep into primals on the right sides of carcasses at approximately 45 min postmortem (Supplemental Figure 1). Each temperature logger contained its own sensor and recorded temperature every minute from 1 h to 21 h postmortem. For the shoulder, temperature loggers were placed in the latissimus dorsi muscle on the lateral side of the carcass near the fourth rib (Addendum 1). Loin temperature loggers were placed in the longissimus dorsi muscle on the lateral side of the carcass near the 10th rib. Ham temperature loggers were placed in the semimembranosus muscle on the medial side of the carcass, posterior to the symphysis pubis bone. Ambient (air) temperature loggers were placed externally to each carcass, connected by a shroud pin in the spinous process of the thoracic vertebrae at approximately the fifth rib. Carcass weight categories were approximately equally represented across kill dates. Despite minor differences in the distribution of carcass weight categories across kill dates, the number of pigs slaughtered at each kill date was approximately equal to ensure a similar chilling load. Carcasses were placed into a cooler (3°C) equipped with an air-cooled medium temperature refrigeration unit (Copeland, Rushville, IN, USA) running 60,000 British thermal units at a −6°C coil temperature. Cooler was also equipped with 2 electric defrost fan coils set to defrost for 40 min, 3 times per day. At 1 h postmortem, ambient (air) temperature averaged from 2.5°C to 6.6°C and declined to an average temperature between −2.3°C and 2.5°C at 11 h postmortem. At 21 h postmortem, average ambient (air) temperature ranged between −0.4°C to 2.0°C. After 21 h, temperature loggers were removed from primals in carcasses, and temperature data were downloaded.
Carcass characteristics
Carcass yield (dressing percentage) was expressed as a percentage determined by dividing HCW, including leaf fat, by the ending live weight. Left sides were ribbed between the 10th and 11th rib with a handsaw to expose the longissimus thoracis (LTL). Back fat thickness was measured at the 10th rib, approximately ¾ the distance of the LTL from the dorsal process of the vertebral column. The surface of the LTL was traced on acetate paper to determine the loin muscle area (LMA). These LTL tracings were measured twice at a later time with a digitizer tablet (Wacom, Vancouver, WA, USA) and Adobe Photoshop CS6 (Adobe Systems Inc., San Jose, CA, USA). Both measurements were averaged to determine the LMA. Following this, the right side of the carcass was weighed and fabricated into primal and subprimal cuts with a shoulder-loin separation between the fourth and fifth rib. Full carcass fabrication methods are described in detail by Metz et al. (2024).
Loin quality evaluation
Loin quality measurements for drip loss, pH, instrumental color, visual color, visual marbling, and subjective firmness were conducted by trained University of Illinois personnel at 1d postmortem on Canadian back loins (NAMP #414; NAMI, 2014). Instrumental color, visual color, visual marbling, subjective firmness, and pH were measured on the ventral surface of the longissimus dorsi at approximately the 10th rib location. Loins were allowed to oxygenate for at least 20 min before quality measurements. Loin ultimate pH was measured with a Hanna Foodcare Portable pH meter calibrated to pH 4 and 7 buffers at 4°C with a Hanna electrode (Hanna 4198163 pH 80 meter, −2.0–20.0 pH/±2000.0 mV; Hanna FC2323 meat-specific electrode, Hanna Instruments, Woonsocket, RI, USA). Instrumental CIE L* (lightness), a* (redness), and b* (yellowness) measurements (Commission Internationale de l’Eclairage [CIE], 1976) were determined with a Minolta CR-400 Chroma meter colorimeter (Konica Minolta, Osaka, Japan) with a 2° observer, an 8 mm closed aperture, a D65 illuminant, and calibrated with a machine-specific white tile. A single trained technician recorded visual color, visual marbling (NPPC, 1999), and subjective firmness (NPPC, 1991).
Loins were cut at the 10th rib location to collect a loin chop sample weighing approximately 50 g for drip loss analysis. Each drip loss chop was weighed (initial weight), attached to a hook, and suspended in a WhirlPak bag (Nasco Sampling, Madison, WI, USA) at 4°C. Chops were reweighed (final weight) after 24 h. Drip loss was expressed as weight lost as a percentage of initial weight.
Loins were sliced into 2.54 cm chops with a push-feed slicer (TREIF PUMA, Marel, Shelton, CT, USA) starting at the 10th rib location. From this reference point, chops were sliced posteriorly toward the sirloin end. The first chop posterior to the 10th rib location, Chop 1, was used for proximate analysis and was vacuum packaged, frozen, and stored at -20°C until use. Sequentially, chops 2 and 3 were used for Warner-Bratzler shear force (WBSF). Chops analyzed for shear force were vacuum packaged and aged for 14 d at 4°C. After 14 d, shear force chops were stored at −20°C until use for the determination of cook loss percentage and WBSF.
Ham and shoulder pH and color evaluation
Trained University of Illinois technicians measured ham quality at 1 d postmortem. For the SM, the lightest colored portion of the medial side was evaluated for color and pH. For the ST, color and pH evaluation were evaluated on the medial side of the muscle using the lightest colored (ST-light) and darkest colored (ST-dark) portions of the muscle as described by Kim et al. (2018). Ultimate pH was measured with a Hanna Foodcare Portable pH meter. Ham muscles were allowed to oxygenate for at least 20 min before evaluation of instrumental L* (lightness), a* (redness), and b* (yellowness) with a Minolta CR-400 colorimeter. The SV and TB muscles were fabricated from pork shoulders and sliced into 2.54-cm chops. Color and pH were measured at 1 d postmortem on the chop surface as described previously.
Moisture and fat percentage
Chops were allowed to partially thaw, to minimize moisture loss, before being trimmed free of subcutaneous fat and homogenized in a food processor (Hamilton Beach, model 70720, Glen Allen, VA, USA). Duplicate 10 g samples from each chop were placed into aluminum tins and covered with 2 sheets of filter paper. Samples were placed in a 110°C oven for a minimum of 24 h to remove moisture from the samples. Following the method described by Novakofski et al. (1989), extraction was completed using Soxhlet extraction, where the sample was washed with a chloroform-methanol solution for a minimum of 8 h. Samples were then dried again in a 110°C oven for a minimum of 24 h. Weights after drying and extraction-drying were used to calculate reported moisture and lipid percentages.
Cook loss and WBSF
Loin chops for WBSF were removed from the freezer and allowed to thaw for approximately 24 h at 4°C. Each chop was weighed individually (initial weight) and cooked on a Farberware Open Hearth grill (model 455N, Walter Kidde, Bronx, NY, USA). Grills were pre-heated for 10 min before cooking. Once heated, the grill heating element temperatures ranged from 271 to 369°C. Grill grate temperatures ranged from 163 to 197°C. Internal temperatures were monitored during cooking using thermocouples (type K, range: −200°C to 1250°C, standard error: ±2.2°C, Omega Engineering, Stamford, CT, USA). Thermocouples were placed at approximately the geometric center of the chops and attached to an Omega HH378 Data Logger Thermometer (Omega Engineering, Norwalk, CT, USA). One chop was cooked to an internal temperature of 31°C, flipped, and cooked to a final internal temperature of 63°C. The other chop was cooked to an internal temperature of 36°C, flipped, and cooked to a final internal temperature of 71°C as described by Nethery et al. (2022). Chops were cooled to room temperature and were weighed a second time to calculate cook loss using the formula:
Four 1.25-cm cores were removed parallel to the muscle fiber direction. Cores were sheared perpendicular to muscle fiber orientation using the Texture Analyzer TA.HD Plus (Texture Technologies Corp., Scarsdale, 134 NY/Stable Microsystems, Goldalming, UK) with a load cell capacity of 100 kg and a blade speed of 3.33 mm/s. The average force to shear of the 4 cores was reported for each sample.
Statistical analysis
Carcass characteristics and meat quality data were analyzed as a one-way analysis of variance (ANOVA) using the MIXED procedure of SAS with the fixed effect HCW category and random effects of sex and sire line. Assumptions of ANOVA were tested with Levene’s test for homogeneity of variance in the GLM procedure of SAS. Normality of distribution of residuals was tested in the UNIVARIATE procedure of SAS. Temperature data were analyzed using the MIXED procedure of SAS (SAS Inst. Inc., Cary, NC, USA) with repeated measures modeling of anatomical carcass locations and HCW category as fixed effects. Ambient (air) temperature served as a random effect in the MIXED model. A compound symmetry covariance structure was used to assume constant variance and equal correlation. The effect of HCW category, carcass primal location, and their interaction was considered significant at P < 0.05. Least square means were calculated for the interaction effects of time and HCW category, as well as time and carcass primal location. Pairwise differences were evaluated with the SLICE option to examine the effect of carcass primal location, HCW category, and their interaction within each hour of postmortem chilling. Although postmortem temperature was recorded and analyzed at each hour from 1 to 21 h, only select time points (every 6 h) are presented in figures to improve figure clarity and interpretability. Full hourly comparisons are described in the results. Pearson correlation coefficients between loin quality traits and loin temperature were determined through the CORR procedure of SAS. Correlations were considered significant at P < 0.05. Correlations were considered weak at r ≤ |0.35|, moderate at |0.36| ≥ r ≤ |0.67|, and strong at r ≥ |0.68| (Taylor, 1990).
Results
Carcass characteristics
As expected, Very Heavy carcasses presented greater HCW (138.4 kg), followed by Heavy (122.0 kg) and Average (104.5 kg) carcasses (P ≤ 0.001; Table 1). In addition, Very Heavy carcasses had greater carcass yield when compared to Average (P < 0.001) and Heavy (P = 0.003) carcasses, but without differences between Average and Heavy carcasses (P = 0.16). Loin muscle area increased (P ≤ 0.001) with each carcass weight category. Similarly, 10th rib back fat depth increased with each carcass weight category (P ≤ 0.03).
Effect of carcass weight on carcass characteristics
| Carcass Weight Category1 | |||||
|---|---|---|---|---|---|
| Item | Average | Heavy | Very Heavy | SEM | P Value |
| Carcass count, n | 20 | 26 | 25 | ||
| Ending live weight, kg | 132.2a | 153.4b | 172.0c | 0.52 | <0.01 |
| Hot carcass weight,2 kg | 104.5a | 122.0b | 138.4c | 0.51 | <0.01 |
| Carcass yield,3 % | 79.04a | 79.52a | 80.49b | 0.25 | <0.01 |
| Longissimus muscle area, cm2 | 49.70a | 55.46b | 60.65c | 1.19 | <0.01 |
| 10th rib back fat depth, cm | 2.21a | 2.63b | 2.93c | 0.11 | <0.01 |
Carcasses were placed into weight categories based on HCW: Average (99–109 kg), Heavy (116–126 kg), Very Heavy (134–144 kg).
Hot carcass weight includes leaf fat.
Carcass yield, % = (hot carcass weight/ending live weight) × 100.
Least-squares means within a row having differing superscripts are considered significant (P ≤ 0.05).
Temperature decline
Carcass weight category affected carcass temperatures during the entire chilling period, 1 h to 21 h postmortem (P ≤ 0.001; Figure 1). Early postmortem (1 h to 2 h), there was already a tendency (P ≥ 0.06) for Very Heavy and Heavy carcasses to be warmer than Average carcasses. However, by 3 h postmortem, Very Heavy carcasses were at least 1.14°C warmer than Average carcasses (P = 0.002), but were not different (P = 0.37) from Heavy carcasses. At 4 h postmortem, Very Heavy carcasses remained warmer than Average carcasses by at least 0.97°C (P = 0.01) and exhibited a tendency (P = 0.09) to be warmer than Heavy carcasses. From 5 h to 17 h, Very Heavy carcasses were consistently warmer than both Average (P ≤ 0.03) and Heavy (P ≤ 0.04) carcasses. At 18 h postmortem, all 3 carcass weight categories differed from one another (P < 0.04) with Very Heavy carcasses being warmest, Heavy carcasses intermediate, and Average carcasses least warm. Finally, from 19 h to 21 h, Very Heavy carcasses were again warmer than both Average (P ≤ 0.03) and Heavy (P ≤ 0.04) carcasses. In general, Very Heavy carcasses exhibited a slower rate of chilling than Heavy and Average carcasses, particularly after 6 h postmortem.
Temperature decline curves of the carcass from 1 h to 21 h postmortem of carcasses categorized as Average (99–109kg), Heavy (116–126kg), and Very Heavy (134–144kg).
As early as 1 h postmortem, hams and loins primals were warmer than shoulders primals (P ≤ 0.001; Figure 2). Specifically, at 1 h postmortem, hams were 4.21°C warmer and loins were 1.56°C warmer than shoulders (P ≤ 0.001), and hams were also 2.71°C warmer than loins (P ≤ 0.001). From 1 h through the end of the chilling period at 21 h postmortem, hams consistently maintained greater temperatures than both shoulders and loins (P ≤ 0.001). Although loin temperatures were initially greater than shoulder temperatures, shoulders and loins did not differ in temperature at 2 h postmortem (P = 0.85). However, by 3 h postmortem, shoulders became 1.22°C warmer than loins (P < 0.001), and this difference persisted through 21 h when shoulders remained 1.40°C warmer than loins (P < 0.001). Overall, hams chilled more slowly than shoulders, which in turn chilled more slowly than loins.
Temperature decline curves of the loin, shoulder, and ham from 1 h to 21 h postmortem.
Tendencies for an interaction between carcass weight category and carcass primal location were observed at multiple times during postmortem chilling (P ≥ 0.08). To highlight differences attributable to carcass weight in each primal, the effect of carcass weight category on temperature was presented separately for each primal (loin, shoulder, and ham). Within the loin primal (Figure 3A), carcass weight categories affected temperature at all time points (P ≤ 0.03). At 1 h postmortem, loin temperatures were greater in Very Heavy and Heavy carcasses compared to Average carcasses (P ≤ 0.01). By 6, 12, and 18 h postmortem, loins from Heavy and Average carcasses were similar in temperature, both of which were lower than loins from Very Heavy carcasses (P ≤ 0.001). By 21 h postmortem, loins from Very Heavy carcasses remained warmer than those from Average carcasses (P = 0.03), with Heavy carcasses intermediate but not different from either (P ≥ 0.11). Within the shoulder (Figure 3B), no differences in temperature were observed among carcass weight categories in the first 12 h postmortem (P ≥ 0.11). However, at 18 and 21 h, shoulders from Very Heavy carcasses were warmer than those from Average carcasses (P ≤ 0.04); while shoulders from Heavy carcasses exhibited intermediate temperature values not different from the other categories (P ≥ 0.11). Within the ham primal (Figure 3C), no temperature differences were detected among carcass weight categories at 1, 6, or 12 h postmortem (P ≥ 0.44). However, at 18 and 21 h postmortem, hams from Very Heavy carcasses were warmer than those from Average carcasses, with shoulders from Heavy carcasses intermediate but not different from either (P ≥ 0.22).
(A) Temperature decline curve of loins from carcasses categorized as Average (99–109kg), Heavy (116–126kg), and Very Heavy (134–144kg). (B) Temperature decline curve of shoulders from carcasses categorized as Average (99–109kg), Heavy (116–126kg), and Very Heavy (134–144kg). (C) Temperature decline curve of hams from carcasses categorized as Average (99–109kg), Heavy (116–126kg), and Very Heavy (134–144kg).
Carcass weight was correlated with loin temperature at each hour from 2 h to 21 h postmortem (P ≤ 0.03; Figure 4). The relationship between loin temperature and carcass weight increased from r = 0.26 at 2 h to a peak at 18 h postmortem (r = 0.54). The strength of the relationship between carcass weight and loin temperature declined slightly after 18 h postmortem, but the relationship was still moderately strong (r = 0.49) until the end of chilling at 21 h. Carcass weight was also correlated with both shoulder and ham temperature from 13 h to 21 h postmortem (P ≤ 0.04). The relationship between shoulder temperature and carcass weight increased from r = 0.25 at 13 h to its peak at 21 h postmortem (r = 0.50). Similarly, the relationship between carcass weight and ham temperature increased from r = 0.26 at 13 h to r = 0.60 at the end of chilling at 21 h.
(A) Pearson correlation coefficients (r) between hot carcass weight and loin temperature during chilling from 1 h to 21 h postmortem. (B) Pearson correlation coefficients (r) between hot carcass weight and shoulder temperature during chilling from 1 h to 21 h postmortem. (C) Pearson correlation coefficients (r) between hot carcass weight and ham temperature during chilling from 1 h to 21 h postmortem. Correlations were only reported when significant at P < 0.05.
Loin quality
Ultimate pH of loins tended to be greater in the Very Heavy carcasses (5.57 pH) compared to Average and Heavy carcasses (both 5.52 pH, P = 0.08; Table 2). No differences were observed among carcass weight categories for ventral loin surface NPPC color, marbling, firmness scores, or drip loss (P ≥ 0.35). Similarly, instrumental color measures (lightness, redness, and yellowness) did not differ (P ≥ 0.91) among carcass weight categories. While extractable lipid percentage was not affected by carcass weight (P = 0.19), moisture content was greater in loins from Average carcasses (73.90%) compared with Very Heavy carcasses (73.19%, P = 0.01). Cook loss and WBSF did not differ among carcass weight categories for loin chops cooked to either 63°C (P ≥ 0.33) or 71°C (P ≥ 0.40).
Effect of carcass weight category on loin and chop quality
| Carcass Weight Category1 | |||||
|---|---|---|---|---|---|
| Item | Average | Heavy | Very Heavy | SEM | P Value |
| Carcass count, n | 20 | 26 | 25 | ||
| Ventral loin surface2 | |||||
| pH | 5.52 | 5.52 | 5.57 | 0.02 | 0.08 |
| NPPC color score3 | 3.33 | 3.29 | 3.28 | 0.12 | 0.96 |
| NPPC marbling score4 | 1.63 | 1.46 | 1.66 | 0.12 | 0.35 |
| NPPC firmness score5 | 3.15 | 3.19 | 3.16 | 0.10 | 0.94 |
| Lightness,6 L* | 49.07 | 48.81 | 48.60 | 0.81 | 0.91 |
| Redness,6 a* | 5.63 | 5.59 | 5.79 | 0.40 | 0.92 |
| Yellowness,6 b* | 10.63 | 10.43 | 10.50 | 0.39 | 0.93 |
| Drip loss,7 % | 5.04 | 5.71 | 4.70 | 0.48 | 0.25 |
| Moisture, % | 73.90a | 73.45ab | 73.19b | 0.19 | 0.02 |
| Extractable lipid, % | 2.97 | 3.14 | 3.48 | 0.21 | 0.19 |
| Aged Loin Chops8 | |||||
| WBSF, kg (63°C) | 3.02 | 3.14 | 3.27 | 0.12 | 0.33 |
| Cook loss,9 % (63°C) | 17.44 | 18.80 | 19.00 | 0.59 | 0.11 |
| WBSF, kg (71°C) | 3.47 | 3.70 | 3.66 | 0.14 | 0.40 |
| Cook loss, % (71°C) | 29.08 | 27.46 | 26.57 | 0.92 | 0.13 |
Carcasses were placed into weight categories based on HCW: Average (99–109 kg), Heavy (116–126 kg), Very Heavy (134–144 kg).
Early postmortem traits were evaluated 1 d postmortem.
NPPC color based on the 1999 standards measured in half-point increments, where 1 = palest, 6 = darkest.
NPPC marbling based on the 1999 standards measured in half-point increments, where 1 = the least amount of marbling, 6 = the most amount of marbling.
NPPC firmness based on the 1991 scale measured in whole point increments, where 1 = softest, 5 = firmest.
L* measures darkness (0) to lightness (100; greater L* indicates a lighter color), a* measures redness (greater a* indicates a redder color), and b* measures yellowness (greater b* indicates a more yellow color).
Drip loss, % = ((Initial wt, g.)/(Final wt., g)) ×100.
Loin chops were aged for 14 d.
Cook loss, % = [(initial weight, kg – cooked weight, kg) ÷ initial weight, kg] × 100.
Least-squares means within a row having differing superscripts are considered significant (P ≤ 0.05).
No correlations were observed between ultimate pH and carcass temperature at any hour from 1 h to 18 h (P ≥ 0.11; Table 3). However, weak positive correlations emerged between 19 and 21 h postmortem (r = 0.23 to 0.31, P ≤ 0.05). Visual color and subjective firmness were not correlated with temperature at any time point (P ≥ 0.19; Table 4). Visual marbling scores were also uncorrelated with temperature during early (1 to 6 h) and late (19–21 h) postmortem periods (P ≥ 0.07) but demonstrated a weak positive correlation from 7 to 18 h (r = 0.24 to 0.30, P ≤ 0.04).
Correlation between postmortem loin temperature from 1 h to 21 h postmortem and loin quality traits1
| Variable | ||||
|---|---|---|---|---|
| Item | pH | Drip Loss,2 % | Moisture, % | Extractable Lipid, % |
| Temp at 1 h | −0.067 | 0.191 | −0.191 | −0.121 |
| (0.58) | (0.13) | (0.11) | (0.32) | |
| Temp at 6 h | 0.071 | −0.078 | −0.142 | 0.157 |
| (0.56) | (0.54) | (0.24) | (0.19) | |
| Temp at 12 h | 0.086 | −0.179 | −0.199 | 0.278 |
| (0.47) | (0.15) | (0.10) | (0.02) | |
| Temp at 18 h | 0.191 | −0.258 | −0.308 | 0.3789 |
| (0.11) | (0.04) | (0.01) | (< 0.01) | |
| Temp at 21 h | 0.311 | −0.270 | −0.325 | 0.36 |
| (0.01) | (0.03) | (0.01) | (< 0.01) | |
Upper row is the correlation coefficient between traits. P value for difference from zero provided in parentheses.
Drip loss, % = ((Initial wt, g.)/(Final wt., g)) ×100.
Correlation between postmortem loin temperature from 1 h to 21 h postmortem and NPPC subjective measurements1
| Variable | |||
|---|---|---|---|
| Item | NPPC Color Score2 | NPPC Marbling Score3 | NPPC Firmness4 |
| Temp at 1 h | −0.194 | −0.118 | 0.038 |
| (0.11) | (0.33) | (0.75) | |
| Temp at 6 h | 0.080 | 0.221 | −0.039 |
| (0.51) | (0.06) | (0.74) | |
| Temp at 12 h | 0.147 | 0.291 | −0.018 |
| (0.22) | (0.01) | (0.88) | |
| Temp at 18 h | 0.129 | 0.259 | −0.029 |
| (0.29) | (0.03) | (0.81) | |
| Temp at 21 h | 0.040 | 0.137 | −0.004 |
| (0.74) | (0.25) | (0.98) | |
Upper row is the correlation coefficient between traits. P value for difference from zero provided in parentheses.
NPPC color based on the 1999 standards measured in half-point increments, where 1 = palest, 6 = darkest.
NPPC marbling based on the 1999 standards measured in half-point increments, where 1 = the least amount of marbling, 6 = greatest amount of marbling.
Ventral loin surface instrumental lightness, redness, and yellowness were not correlated with temperature at any time point from 1 h to 21 h postmortem (P ≥ 0.09; Table 5). Drip loss demonstrated no association with temperature from 1 to 17 h postmortem (P ≥ 0.06), but a weak negative correlation from 18 to 21 h postmortem (r = −0.26 to −0.29, P ≤ 0.04). Moisture content was not correlated with temperature from 1 to 13 h postmortem (P ≥ 0.08), but weak negative correlations appeared from 14 to 21 h postmortem (r = −0.24 to −0.33, P ≤ 0.04). Extractable lipid content was not associated with temperature from 1 h to 10 h (P ≥ 0.07) but demonstrated weak correlations from 11 to 15 h postmortem (r = 0.24 to 0.33, P ≤ 0.04), and moderate correlations from 16 to 21 h postmortem (r = 0.36 to 0.38, P ≤ 0.002).
Correlation between postmortem loin temperature from 1 h to 21 h postmortem and loin instrumental color measurements1
| Variable | |||
|---|---|---|---|
| Item | Lightness,2 L* | Redness,3 a* | Yellowness,4 b* |
| Temp at 1 h | 0.108 | −0.031 | −0.041 |
| (0.37) | (0.80) | (0.73) | |
| Temp at 6 h | −0.154 | −0.031 | 0.081 |
| (0.20) | (0.80) | (0.50) | |
| Temp at 12 h | −0.193 | 0.109 | 0.151 |
| (0.11) | (0.37) | (0.21) | |
| Temp at 18 h | −0.169 | 0.130 | 0.126 |
| (0.16) | (0.28) | (0.30) | |
| Temp at 21 h | −0.057 | 0.084 | 0.115 |
| (0.63) | (0.48) | (0.34) | |
Upper row is the correlation coefficient between traits. P value for difference from zero provided in parenthesis.
L* measures darkness (0) to lightness (100; greater L* indicates a lighter color).
a* measures redness (greater a* indicates a redder color).
b* measures yellowness (greater b* indicates a more yellow color).
NPPC firmness based on the 1991 scale measured in whole point increments, where 1 = softest, 5 = firmest.
There were no correlations between WBSF and carcass temperature at any time point for chops cooked to either 63°C (P ≥ 0.43) or 71°C (P ≥ 0.42; Table 6). Cook loss percentage for chops cooked to 63°C was not correlated with carcass temperature from 2 h to 21 h postmortem (P ≥ 0.08), though a weak correlation was observed at 1 h postmortem (r = 0.27, P = 0.02). For chops cooked to 71°C, no early (1–4 h) correlations were observed (P ≤ 0.07), but weak negative correlations were present from 5 to 12 h (r = −0.23 to −0.35, P ≤ 0.04) and from 16 h to 20 h postmortem (r = −0.33 to −0.23, P ≤ 0.05). This correlation was slightly stronger between 13 to 15 h (r = –0.36, P ≤ 0.002).
Correlation between postmortem loin temperature from 1 h to 21 h postmortem and Warner-Bratzler shear force and cook loss of loin chops1
| Variable | ||||
|---|---|---|---|---|
| Item | WBSF (63°C) | Cook Loss2 (63°C) | WBSF (71°C) | Cook Loss2 (71°C) |
| Temp at 1 h | 0.092 | 0.268 | 0.042 | −0.050 |
| (0.44) | (0.02) | (0.73) | (−0.68) | |
| Temp at 6 h | −0.050 | −0.034 | −0.616 | −0.260 |
| (0.68) | (0.78) | (0.61) | (0.03) | |
| Temp at 12 h | −0.071 | −0.029 | −0.064 | −0.354 |
| (0.55) | (0.81) | (0.60) | (< 0.01) | |
| Temp at 18 h | −0.080 | 0.111 | −0.013 | −0.292 |
| (0.51) | (0.36) | (0.92) | (0.01) | |
| Temp at 21 h | −0.019 | 0.209 | 0.098 | −0.196 |
| (0.87) | (0.08) | (0.42) | (0.10) | |
Upper row is the correlation coefficient between traits. P-value for difference from zero provided in parentheses.
Cook loss, % = [(initial weight, kg – cooked weight, kg) ÷ initial weight, kg] × 100.
Ham and shoulder quality
For both the SV and TB muscles, there were no differences in ultimate pH or instrumental color between carcass weight categories (P ≥ 0.11; Table 7).
Effect of carcass weight category on shoulder quality
| Carcass Weight Category1 | |||||
|---|---|---|---|---|---|
| Item | Average | Heavy | Very Heavy | SEM | P Value |
| Carcass count, n | 20 | 26 | 25 | ||
| Serratus ventralis2 | |||||
| pH | 5.82 | 5.88 | 5.87 | 0.06 | 0.71 |
| Lightness,3 L* | 42.69 | 42.62 | 42.35 | 0.75 | 0.94 |
| Redness,4 a* | 15.76 | 16.33 | 16.27 | 0.44 | 0.58 |
| Yellowness,5 b* | 5.88 | 6.88 | 6.50 | 0.42 | 0.21 |
| Triceps brachii2 | |||||
| pH | 5.90 | 5.83 | 5.92 | 0.06 | 0.56 |
| Lightness,3 L* | 41.12 | 39.57 | 40.06 | 0.55 | 0.11 |
| Redness,4 a* | 15.40 | 15.45 | 15.13 | 0.66 | 0.92 |
| Yellowness,5 b* | 4.52 | 5.24 | 5.07 | 0.31 | 0.21 |
Carcasses were placed into weight categories based on HCW: Average (99–109 kg), Heavy (116–126 kg), Very Heavy (134–144 kg).
Measurement was taken on the chop surface.
L* measures darkness (0) to lightness (100; greater L* indicates a lighter color).
a* measures redness (greater a* indicates a redder color).
b* measures yellowness (greater b* indicates a more yellow color).
Ultimate pH did not differ among carcass weight categories (P ≥ 0.11) for the ST-light, ST-dark, or SM muscles (Table 8). Instrumental lightness (L*) of the ST-light was also similar across carcass weight categories (P = 0.15). However, the ST-light from Average carcasses was redder (greater a* values) than that from Heavy and Very Heavy carcasses (P ≤ 0.03), with no differences in redness observed between Heavy and Very Heavy carcasses (P = 0.68). Similarly, the ST-light of Average carcasses was more yellow (greater b* values) than from Heavy carcasses (P = 0.004), while the yellowness of the ST-light from Very Heavy carcasses was intermediate and not different from either Average or Heavy carcasses (P ≥ 0.08).
Effect of carcass weight category on ham quality at 1 d postmortem
| Carcass Weight Category1 | |||||
|---|---|---|---|---|---|
| Item | Average | Heavy | Very Heavy | SEM | P value |
| Carcass count, n | 20 | 26 | 25 | ||
| Semitendinosus, Light2 | |||||
| pH | 5.70 | 5.76 | 5.83 | 0.05 | 0.11 |
| Lightness,3 L* | 55.71 | 52.86 | 54.88 | 1.14 | 0.15 |
| Redness,4 a* | 11.32a | 9.68b | 9.92b | 0.48 | 0.03 |
| Yellowness,5 b* | 7.34a | 5.19b | 6.05ab | 0.55 | 0.02 |
| Semitendinosus, Dark6 | |||||
| pH | 5.85 | 5.90 | 5.89 | 0.05 | 0.76 |
| Lightness,3 L* | 42.78b | 44.99a | 43.29b | 0.68 | 0.04 |
| Redness,4 a* | 16.31 | 14.88 | 15.63 | 0.54 | 0.14 |
| Yellowness,5 b* | 6.07a | 4.58b | 4.76b | 0.39 | 0.01 |
| Semimembranosus7 | |||||
| pH | 5.62 | 5.63 | 5.65 | 0.02 | 0.49 |
| Lightness,3 L* | 52.86 | 51.71 | 53.39 | 1.00 | 0.39 |
| Redness,4 a* | 10.27 | 10.27 | 10.66 | 0.45 | 0.74 |
| Yellowness,5 b* | 4.86 | 3.63 | 4.87 | 0.50 | 0.09 |
Carcasses were placed into weight categories based on HCW: Average (99–109 kg), Heavy (116–126 kg), Very Heavy (134–144 kg).
Measurement taken on the medial side of the semitendinosus.
L* measures darkness (0) to lightness (100; greater L* indicates a lighter color).
a* measures redness (greater a* indicates a redder color).
b* measures yellowness (greater b* indicates a more yellow color).
Measurement taken on the distal side of the semitendinosus from the femur.
Measurement taken on the medial side at the blonde spot.
Least-squares means within a row having differing superscripts are considered significant (P ≤ 0.05).
For the ST-dark, Heavy carcasses had lower lightness (L*) values compared to both Average and Very Heavy carcasses (P = 0.04), which did not differ from each other (P = 0.58). Redness (a*) did not differ between carcass weight categories for the ST-dark (P ≥ 0.14). However, Average carcasses demonstrated a more yellow (greater b* value) ST-dark than both Heavy and Very Heavy carcasses (P = 0.01), which again did not differ from each other (P = 0.72). No differences in lightness or redness were observed between carcass weight categories for the SM muscle (P ≥ 0.39). However, the SM tended to be bluer in color (lower b* value) in Heavy carcasses than in the Average and Very Heavy carcasses (P = 0.09).
Discussion
Consistent with previous studies (Coulter et al., 1995; Daudin and Kuitche, 1996; Overholt et al., 2019; Price et al., 2022), heavier carcasses in the present study exhibited slower chilling rates. Price et al. (2022) reported that increasing carcass weight by 10 kg resulted in a decrease in chilling rate of 0.25°C/h during the first 5 h postmortem, with 25.4% of the variation in chilling rate due to carcass weight. In the present study, although temperature differences among carcass weight categories were relatively small during the first 6 h postmortem, these differences became more pronounced by 21 h, indicating a compounding effect over time. The reduction in temperature decline observed in heavier carcasses may be attributed to decreased carcass surface area exposed to air movement relative to total volume as carcass weights increase. This, in turn, may slow the release of heat from the surface of the carcass (Overholt et al., 2019). Additionally, although minor differences in 10th rib back fat depth were observed between HCW categories, subcutaneous fat distribution is not uniform across primals, complicating the interpretation of its specific insulative effects.
Hams consistently chilled more slowly than loins from 1–21 h postmortem, confirming prior observations (Arkfeld et al., 2016; Jones et al., 1993; Melody et al., 2004; Overholt et al., 2019; Rosenvold et al., 2010). Arkfeld et al. (2016) and Overholt et al. (2019) both reported that hams chilled more slowly than loins, no matter the carcass weight, with loins reaching ambient temperature sometime during chilling and hams not reaching ambient temperature during the 21 h postmortem, where temperature was recorded. In pigs lighter than the current industry standard, Melody et al. (2004) also reported that after 24 h of chilling, the semimembranosus exhibited increased temperatures compared with longissimus dorsi and psoas major muscles. Despite a wealth of information on postmortem temperature decline of hams and loins, the temperature decline of shoulder primals had not been extensively investigated before the present study, which may be increasingly relevant for novel fresh chop fabrication as primal weights increase (Metz et al., 2024). Notably, in the present study, shoulder primals exhibited a chilling pattern intermediate between loins and hams, with loins cooling more rapidly and hams more slowly. This differs from previous research involving lighter-weight pigs, where shoulders were reported to chill similarly to hams and slower than loins in both rapid and stepwise chilling systems (James et al., 1983; Rosenvold et al., 2010).
The within-primal temperature figures help illustrate the interaction observed and highlight how carcass weight affects chilling rate within each primal, which is more relevant to commercial processing than comparing across different primals. Where carcass weight effects on temperature decline of shoulder and ham primals only materialized in late chilling (18 h postmortem and after), carcass weight categories influence the rate of loin primal cooling during the entire chilling period. These findings highlight the need for temperature management in heavier carcasses to be primal-specific.
Several studies have reported decreases in slice shear force values with increased carcass weight. For example, et al. (2017) and Price et al. (2022) reported decreases of 1.26 kg and 1.01 kg, respectively, in slice shear force for every 10 kg increase in carcass weight, using chops cooked to 71°C. This slice shear force reduction in tenderness has been linked to slower postmortem temperature decline, which may prolong enzymatic activity and extend the duration of postmortem metabolism (Moeller et al., 1976, 1977). Conversely, other studies have observed no effect of increased carcass weight on shear force (Beattie et al., 1999; Cisneros et al., 1996; Latorre et al., 2004; Rice et al., 2019). In the present study, objective tenderness of loin chops cooked to either 63°C or 71°C did not differ among carcass weight categories, despite differences in loin temperature at 21 h postmortem. Despite differences in grill heating element and grill grate temperatures, chops were cooked to a precise 63 or 71°C using constant temperature monitoring. Importantly, prior research has demonstrated that cooking rate only explained 3.2% and 5.4% of variability in WBSF of pork chops cooked to 63°C and 71°C, respectively (Nethery et al., 2022). Likewise, no differences were observed in other key loin quality traits, including color, marbling, and drip loss. It is important to note that this study was conducted under conventional chilling conditions, whereas prior studies, representative of current market weights, were performed in large commercial operations employing blast-chilling systems (Harsh et al., 2017; Price et al., 2022). Differences in chilling systems may partially account for the variation in observations across studies.
Weak correlations between loin temperature and ultimate pH were observed only in late chilling (19 h to 21 h postmortem), which was unexpected given their established relationship during postmortem metabolism (Briskey, 1964; Briskey and Wismer-Pedersen, 1961). Additionally, early postmortem carcass temperature has been reported to influence the rate of tenderization (Huff-Lonergan et al., 2010; Marsh, 1977). However, in the present study, no correlations were detected between loin temperature and either ultimate pH or objective tenderness measures across most of the chilling period.
Instrumental color values for the SV and TB shoulder muscles in the present study align with those reported by Bohrer et al. (2024), with no changes observed across carcass weight categories. Similarly, SM muscle color was unaffected by increasing carcass weight, contrasting with earlier reports of increased redness in heavier carcasses (Đurkin et al., 2012; Harsh et al., 2017). Specifically, Đurkin et al. (2012) noted a 0.34 unit increase in SM a* values per 10 kg increase in live weight. In contrast, increases in carcass weight were associated with decreased instrumental yellowness (b*) in ham muscles. Both the ST-dark and ST-light became less yellow in color as weight increased, and a similar trend was observed in the SM. While Bohrer et al. (2024) reported that ST and SM were inherently more yellow than loin chops, the relevance of changes in yellowness to consumer perception remains unclear. As heavier carcasses yield larger muscle dimensions, particularly in the shoulder and ham, future work should evaluate the sensory attributes and eating quality of these muscles to assess their viability as alternatives to traditional pork loin chops.
Conclusion
Increasing carcass weight up to 144 kg resulted in slower temperature decline, but did not adversely affect loin, shoulder, or ham quality traits. Notably, the instrumental color of the shoulder and ham muscles remained relatively consistent across weight categories. Additionally, differences in chilling behavior among primals may require consideration in commercial processing to optimize chilling strategies across carcass regions.
Conflict of Interest
The authors declare no conflicts of interest regarding the content of this manuscript.
Author Contributions
Kaitlin Guthrie conducted the study, collected data, analyzed data, and wrote the draft manuscript; Joe Metz collected data, and reviewed the manuscript; Bailey Harsh conceived the study, secured funding, edited the manuscript, and provided supervision.
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Image of temperature probe location in ham, loin, and shoulder of pork carcasses. Ambient (air) temperature probes were secured to the outside of each side by shroud pin into the neck bones.