J. C. Forrest

Development of technology for the early post mortem prediction of water holding capacity and drip loss in fresh pork.

Two different technologies were tested on the slaughterline for their ability to predict drip loss at 24 h, namely near infrared reflectance (NIR) and impedance measurements using a tetra polar measuring geometry at a frequency of 1000 Hz. The results demonstrate that NIR measurements (900-1800 nm) acquired during a 6 min period starting only 30 min post exsanguination through a fibre optic probe in combination with multivariate data analysis can be used for predicting drip loss 24 h after slaughter. A correlation higher than 0.8 was observed for a trial on 99 carcasses measured at a commercial slaughterhouse. The tetrapolar impedance measurements did not perform as well as NIR yielding a correlation of 0.5 with 24 h drip loss.

Early postmortem electrical stimulation simulates PSE pork development

Carcasses from 64 gilts were subjected to electrical stimulation (ES) at 3, 15, 25, 35, 45, and 55 min postmortem or were untreated (NS). Temperature and pH of longissimus muscles were recorded at 1, 7, 14, 20, 30, 40, 50, and 60 min, and 24 h postmortem. Muscle samples were collected at 1, 30 and 60 min, and 24 h for determining glycolytic metabolite concentrations. ES at 3, 15, and 25 min resulted in lower (P<0.05) muscle pH, but stimulation after 25 min had no effect on muscle pH. Likewise, ES prior to 25 min resulted in greater (P<0.05) muscle temperatures. Muscle lactate concentrations were greater (P<0.05) in carcasses stimulated before 45 min postmortem. Glucose 6-phosphate concentration decreased (P<0.05) during the first hr postmortem and increased (P<0.05) thereafter. ES of carcasses at 45 and 55 min resulted in higher (P<0.05) concentrations of muscle glucose 6-phosphate at 24 h compared with NS and early-stimulated carcasses. Muscle glycogen concentrations at 30 min in carcasses stimulated at 3, 15 and 25 min were lower (P<0.05) than NS carcasses. Carcasses stimulated at 3 and 15 min exhibited lower (P<0.05) concentrations of muscle glycogen at 60 min than NS carcasses. Carcasses stimulated at 3 and 15 min postmortem exhibited lower (P<0.05) color and firmness scores, while ES at 3 and 25 min postmortem resulted in lower (P<0.05) water holding capacity. ES had no significant effect on CIE L(∗), a(∗), b(∗), or 24 h muscle pH. These data show that ES of pork carcasses during the first 25 min postmortem creates PSE-like quality characteristics and suggest that ES is a potential model for studying pork quality development.

Effect of halothane genotype on porcine meat quality and myoglobin autoxidation.

The objective of this study was to determine effects of light (40-80 kg) or heavy (100-130 kg) slaughter weight and halothane status (positive, nn; negative, NN; and heterozygous, Nn), on meat quality. Longissimus muscle (LM) pH at 45 min (pH(45)) post-exsanguination was 6.25, 6.03, and 5.84 (different at p < 0.01) for NN, Nn, and nn genotype, respectively. At heavier weights (100-130 kg), genotype correlated (r = -0.71) with LM pH(45), 10th costae LM (TENLM) color score (r = -0.55), TENLM Hunter L(∗)-value (r = 0.47), water holding capacity (r = 0.42) and TENLM subjective firmness-wetness score (r = 0.51). Rate constants for metmyoglobin accumulation and oxymyoglobin autoxidation, indicators for fresh meat color stability, increased (p < 0.05) with decreasing pH. Color stability for NN muscle was more stable than nn muscle (p < 0.05). Electrofocusing of myoblobin revealed two bands (MW 17.10(3)) at pI 6.1 and 6.5 across genotypes. Because differences were not observed across genotypes, an observed increase (p < 0.05) in 24 hr myoglobin autoxidation rate constant (associated with increased expression of the HAL gene) are presumed dependent upon post-mortem muscle changes. These data show that changes in halothane status affect fresh pork quality and that lowered meat quality results in further color destruction due to altered chemical reactions involving myoglobin oxidation.

Bovine muscle shortening and protein degradation after electrical stimulation, excision and chilling☆

Electrical stimulation-dependent improvement in beef tenderness resulted from mechanisms other than avoidance of cold shortening in excised muscle chilled at a normal rate (10°C at 10h post-stimulation). At normal chilling rate, electrical stimulation enhanced degradation of the myofibrillar proteins, alpha actinin and troponin-T, and increased the amount of a 30 000 dalton protein, as assessed by gel electrophoresis, whereas sarcomere lengths were not different from unstimulated muscle. Under slightly accelerated chilling conditions (10°C at 5 h post stimulation), electrical stimulation prevented cold shortening but the meat was more tender than, and had the same sarcomere length as, unstimulated muscle chilled to 10°C in 10 h. Electrical stimulation did not improve the tenderness of beef chilled at a rapid rate (10°C at 2 h post stimulation), nor did it prevent cold shortening when muscles were chilled rapidly.

Effect of heating rate on shortening, ultrastructure, and fracture behavior of prerigor beef muscle

Rapidly heated prerigor beef is tender because of incompletely described myofibrillar disruption and tissue fracture. This study was designed to evaluate the effects of heating rate on heat-induced myofibrillar shortening, ultrastructural changes, and fracture behavior in prerigor triceps brachii muscle. Rapid heating (2°C/2 min) to 53°C caused (P < 0·05) more severe myofibrillar shortening in a shorter time and at higher muscle pH and temperature, less muscle weight loss, and shorter sarcomeres than slow heating (2°C/12 min) to 47 or 53°C. Rapid heating caused more extensive degradation of A and I bands, greater loss of the tridimensional pattern of myofibrils, more fragmentation and melting of myofibrils, widened intermyofibrillar spaces, and maximum separation of fiber bundles as compared to slow heating. Slow heating caused extensive shortening but not extensive degradation and disruption of myofibrils. Muscles slowly heated to 53°C sustained greater loss of structural integrity than those slowly heated to 47°C, but fracture behavior was similar. Separation and fracture occurred near the perimysial/endomysial junction in all heated samples, but the perimysium remained affixed to the endomysium at one side of the interface in many rapidly heated samples. Longitudinal fractures showed a granular endomysium and large numbers of supercontraction nodes alternating with areas of sarcolemmal membrane fragmentation and fiber tearing in rapidly heated samples. Alterations of myofibrillar ultrastructure and fiber structure, and separation of bundles, may account for enhanced tenderness of rapidly heated prerigor muscle.

Performance of Alternative Component Pricing Systems for Pork

One method of implementing value-based marketing is a component pricing system. This research develops and evaluates alternative component pricing systems for pork. Two electronic technologies for estimating carcass components (optical probe and electromagnetic scanner) were evaluated on two sets of data representing different populations. Model accuracy increased as additional components were added.

Evaluation of the prediction of alternative measures of pork carcass composition by three optical probes

The accuracy of 3 optical probes (HGP4 Hennessey Grading Probe, Destron-Feering PG-100 probe, and Giraldo OPTO-Electronic PG-200 probe) to predict the carcass percentage of 5 alternative measures of carcass composition (fat-tissue-free lean, lipid-free soft tissue, lipid-free lean, total fat tissue, and soft tissue lipid) was evaluated on 203 barrows and gilts of 7 genetic populations. The optical probe backfat depths were more closely correlated (P < 0.001, 0.963 to 0.983) than the LM depths (r = 0.695 to 0.734). The optical probe backfat depths were related to lean percentage (r = -0.82 to -0.88), total fat tissue percentage (r = 0.84 to 0.88), and soft tissue lipid percentage (r = 0.86 to 0.87). Optical probe LM depths were weakly related (P < 0.05; r = 0.23 to 0.34) to measures of carcass lean percentage and total fat tissue percentage (r = -0.16 to -0.26). Fat-free lean percentage was predicted with residual SD (RSD) of 3.7% for equations including last-rib midline backfat thickness, 2.4 to 2.7% for equations including optical probe backfat and LM depth, and 2.3% for ribbed carcass measurements. The RSD for the optical probe equations ranged from 2.1 to 2.4% for lipid-free soft tissue percentage and from 2.0 to 2.3% for lipid-free lean percentage. The RSD for the optical probe equations ranged from 2.9 to 3.3% for total fat tissue percentage and 2.5 to 2.8% for soft tissue lipid percentage. Quadratic and cross-product variables of optical probe fat depth, LM depth, and carcass weight were significant (P < 0.05) and reduced the RSD of the equations. Optical probe backfat and LM measurements can be used to predict alternative measures of carcass composition. The predicted relationships in fat-free lean percentage to backfat depth were nearly identical for each optical probe.

Prediction of lean and fat composition in swine carcasses from ham area measurements with image analysis.

Video images of ham cross-sections were recorded from 71 pork carcasses (ranging in weight from 72 to 119kg). Three sets of prediction equations were developed to estimate pork carcass lean and fat composition from video image analysis (VIA) of ham cross-sectional area measurements, 10th rib back fat depth (TENFAT) and hot carcass weight (HCKg). Carcass data of dissected lean and fat in the four primal cuts (ham, loin, Boston button and picnic shoulder) were used as dependent variables in establishing regression equations. The first set of equations combined VIA ham measurements and total ham weight (HTKg). Regression models containing the single variable HTKg times ham percentage lean area (Vol. 1) or HTKg times ham percentage fat area (Vol. 2) accounted for 88% and 68% of the variation in total carcass lean weight (CLKg) and total carcass fat weight (CFKg) from the right side of each carcass, respectively. The second set of equations combined VIA ham measurements and TENFAT (cm). Multiple regression models involving TENFAT, Vol. 1, and Vol. 2 accounted for 91% and 90% of the variation in CLKg and CFKg. The third set of equations used VIA ham measurements, TENFAT and HCKg. Carcass lean weight was best predicted by HCKg, TENFAT, and ham lean area (HLA) (R(2)=.92). Carcass fat weight was best predicted by HCKg, TENFAT, and Vol. 2 (R(2)=.91). Overall correlations showed a high association between Vol. 1 and CLKg (r=.94, P<.0001) and Vol. 2 and CFKg (r=.83, P<.0001). Ham lean area was related to CLKg (r=.74, P<.0001) and ham fat area to CFKg (r=.81, P<.0001). The results of this study indicated video image analysis of ham cross-section slices combined with backfat depth at the 10th rib can be used for accurate estimation of total carcass lean or fat composition.

Shortening and tenderness of pre-rigor heated beef: Part 1 — Effect of heating rate on muscles of youthful and mature carcasses

Pre-rigor cooked beef is tender if the cooking produces severe shortening. This study was conducted to compare the effects of different heating rates on shortening and tenderness. Myofibrillar and cooking shortening and related changes were measured with physiograph recordings on pre-rigor M. triceps brachii strips suspended in paraffin oil during heating. Warner-Bratzler shear values were determined on M. triceps brachii samples heated at approximately the same rates at which the muscle strips were heated. Rapid heating (2°C/2min) produced more (p < 0·01) severe myofibrillar shortening that was complete at higher (p < 0·01) muscle temperatures than slow heating (2°C/12 min). Regardless of animal age, rapid heating resulted in a cooked product that was more (p < 0·01) tender than that produced by slow heating in the pre-rigor state and slow heating resulted in a more (p < 0·01) tender product than that achieved by rapid heating in the post-rigor state. Data on muscle shortening and from differential scanning calorimetry suggest that the tenderness produced from pre-rigor rapid heating results from a heat-induced active contraction.

Moisture absorption early postmortem predicts ultimate drip loss in fresh pork

Water-holding capacity is the ability of meat to hold moisture and is subject to postmortem metabolism. The objective of this study was to characterize the loss of moisture from muscle postmortem and investigate whether these losses are useful in predicting the ultimate drip loss of fresh pork. Cotton-rayon absorptive-based devices were inserted in the longissimus dorsi muscles of pork carcasses (n = 51) postmortem and removed at various intervals for 24h. Greatest moisture absorption was observed at 105 min post exsanguination. Drip loss varied (0.6-15.3%) across carcasses. Individual absorption at 75 min correlated (r = 0.33) with final drip loss. Correlations improved using individual absorption values at 90 min (r = 0.48) and accumulated absorption values at 150 min (r = 0.41). Results show that significant moisture is lost from muscle tissue early postmortem and suggest that capture of this moisture may be useful in predicting final drip loss of fresh meat.