Effect of wavelength on spatial measurements of light scattering for the measurement of pork quality.

White light from a xenon arc was focused onto the upper surface of 25-mm-thick transverse sections of pork longissimus muscle. A servo motor moved an optical fiber across the lower surface of the muscle to collect transmitted light, which then was passed through a grating monochromator and onto a photomultiplier for spatial measurements of scattering (SMS) and transmittance spectra. The SMS were calculated as the slope of the logarithm of transmittance relative to path length through the sample (which was calculated trigonometrically). Pale, soft, exudative (PSE) pork was measured with an index that included a subjective evaluation of meat color and objective measurements of reflectance, drip loss, and centrifugation fluid loss. The strongest correlation of SMS with PSE was at 610 nm (r = .86, P less than .005) and the strongest correlation of transmittance with PSE was at 650 nm (r = -.95, P less than .005). This supports the use of a red laser at 633 nm for the detection of PSE pork.     

Comparison of histochemical characteristics in various pork groups categorized by postmortem metabolic rate and pork quality

The purpose of the present study was to investigate the variations in histochemical characteristics of muscle samples segregated according to metabolic rates (MR) and pork quality attributes. A total of 231 crossbred Duroc x (Yorkshire x Landrace) pigs was evaluated. Samples of the LM were taken to evaluate histochemical characteristics, postmortem MR, and meat quality. Samples were classified into fast, normal, and slow MR groups based on muscle pH at 45 min and R-value. Drip loss and lightness (L*) were used to assign samples to 1 of 4 quality classes. Pale, soft, and exudative pork belonging in the fast group had the greatest (P < 0.05) percentage of type IIb fibers, and RSE (reddish-pink, soft, and exudative) pork belonging in the fast group had a similar tendency. Additionally, RFN (reddish-pink, firm, and nonexudative) pork belonging in the normal group showed a lower (P < 0.05) percentage of type IIb fibers than PSE or RSE, regardless of MR, and DFD pork had the lowest (P < 0.05) percentage of type IIb fibers. In general, the fast-glycolyzing PSE pork with the lowest pH at both 45 min and 24 h had greater percentages of type IIb fibers than the fast-glycolyzing RFN pork. There were more fiber-type composition differences between quality classes in pork undergoing a fast rate of metabolism compared with pork undergoing a normal rate of metabolism. It can be concluded that muscle histochemical characteristics are associated with early postmortem MR, the extent of glycolysis, and, thereby, pork quality; however, these effects are limited to the pigs exhibiting a fast glycolytic rate.     

Evaluation of factors in development of Vis/NIR spectroscopy models for discriminating PSE,DFD and normal broiler breast meat

1. To evaluate the performance of visible and near-infrared (Vis/NIR) spectroscopic models for discriminating true pale, soft and exudative (PSE), normal and dark, firm and dry (DFD) broiler breast meat in different conditions of preprocessing methods, spectral ranges, characteristic wavelength selection and water-holding capacity (WHC) indexes were assessed.

2. Quality attributes of 214 intact chicken fillets (pectoralis major), such as lightness (L*), pH and WHC indicators including drip loss (DL), water gain and expressible fluid were measured. Fillets were grouped into PSE, normal and DFD categories based on combination of L*, pH and WHC threshold criteria. Classification models were developed using support vector machine based methods on characteristic wavelengths selected from the unprocessed or 2nd-derivative spectra, respectively, in three spectral subsets of 400–2500, 400–1100 and 1100–2500 nm.

3. Better classification of three meat groups was obtained based on unprocessed spectra (72–94%) than 2nd-derivative spectra (55–72%). The classification based on 400–2500 nm (91% average) and 400–1100 nm (89% average) performed better than that on 1100–2500 nm (78% average). In terms of the three different WHC indicators, the combination of L*, pH and DL produced better results than the other two groups, with recognition accuracy of 94.4% using 400–2500-nm range.

4. These analytical results suggest that for a better classification of true PSE, normal and DFD broiler breast meat with Vis/NIR spectra, unprocessed spectra wavelengths should be used, ranges of 400–1000 nm should be included in the data collection, and DL as an indicator of WHC might provide a better prediction model.     

Duplication of the pale, soft, and exudative condition starting with normal postmortem pork

The objective of the current study was to create an in vitro model that duplicated the development of PSE pork. Postrigor pork chops with various pH values and normal color were vacuum-packaged, and heated at approximately 42 degrees C for various times (0, 15, 30, 60, 120, or 240 min), or heated to temperatures that occur early postmortem (34, 37, 39, or 42 degrees C for 60 or 120 min) in a water bath. Chops were cooled and allowed to bloom, after which changes in Minolta and Hunter color values were assessed, and purge loss was determined. Warming postrigor pork with normal color and pH to early postmortem body temperature for various times successfully duplicated the characteristics of PSE pork. After 60 to 120 min at 42 degrees C or above, chops with pH < 5.8 lightened until L values were similar to those typical of PSE pork (Minolta L = 61.0). Change in chop color depended on length of time the samples were warmed, as well as on pH. Below 34 degrees C, temperature had no (P > or = 0.28) effect on color (Minolta L, a, b, and Hunter L*, a*, b*); however, at higher temperatures, color change depended on pH and warming time. A comparison of the time and temperature relationships for changes in lightness and purge suggested that the mechanisms of the two processes are not identical. The similarities in the dynamic range of color change, change in absolute color values, and time frame for changes in vitro and in vivo suggest similarity of the processes creating PSE in a carcass and in the in vitro model.     

Rheological characteristics of fresh and frozen PSE, normal and DFD chicken breast meat

1. Textural and rheological differences among broiler breast meat ranging from pale, soft and exudative (PSE) to dark, firm and dry (DFD) in their fresh and frozen (and thawed) forms were investigated. 2. The PSE meat showed significantly higher lightness values and lower pH and water holding capacity values than normal and DFD meats; DFD meat was also significantly different from normal meat. 3. During cooking, PSE meat lost significantly more liquid and produced a softer gel than normal or DFD meats; texture profile analysis parameters were lower for the PSE meat. 4. The storage modulus values (G', rigidity of elastic response of the gelling material) showed that DFD meat produced a more rigid gel during cooking (especially above 54 degrees C) and later during cooling (back to 30 degrees C) compared with the PSE meat. 5. Freezing resulted in a trend of lower G' values before, during and after cooking. The results indicated that meat proteins were damaged during freezing and PSE meat was more severely affected, or that more protein denaturation occurred in the PSE meat.     

Glycolytic potential of red, soft, exudative pork longissimus muscle

Red, soft, exudative (RSE) pork is red as "normal" pork and exudative as PSE pork. The origin of RSE quality is unknown. In the present study, we determined whether the occurrence of RSE pork is related to the presence of the RN (Rendement Napole) gene. A glycolytic potential [= 2 x (glucose + glycogen + glucose-6-phosphate) + lactate] of > 180 micromol lactate/g of meat was used as indicator for presence of the RN gene. At 1 d postmortem, pork loin samples were collected at a commercial slaughter plant, and meat quality characteristics and glycolytic potential were determined. Glycolytic potential of RSE pork (n = 42) was higher (P < .01) than that of RFN (red, firm, nonexudative) pork (n = 25): 137 vs 110 micromol lactate/g of muscle. The glycolytic potential of PSE pork (n = 28) was 161 micromol lactate/g of muscle, which was higher (P < .01) than the glycolytic potential of RFN or RSE pork. Using a glycolytic potential of 180 micromol lactate/g of muscle as suggestive for the presence of the RN gene, four (10%) of the RSE samples were from RN carriers. By the same criterion, the PSE group contained nine (32%) RN gene carriers. These results suggest that the occurrence of RSE quality is not related to the presence of the RN gene.     

Using pork to teach students quality variations and how they are measured. 1998 UW-AS-305 Class.

Using a total of eight pork loins representing DFD (dark, firm, and dry) and PSE (pale, soft, and exudative) conditions, 35 students conducted a series of objective and subjective measurements to demonstrate extremes in meat quality in a single 2-h laboratory. Students learned to objectively assess appearance, water-holding and water-binding capacity, ultimate pH (pHu), and shear force (cooked samples) by operating seven commonly known laboratory instruments. They also learned how to prepare and present samples for organoleptic analysis using hedonic and triangle tests. Finally, the students learned the factors related to meat quality and how extremely they can vary. Within one laboratory, they observed that DFD, when compared with PSE, averaged 1.5 units higher in pHu, 4.7% (absolute) less drip loss, bound 136% (absolute) more water, was darker in color (26 units lower L* value), was firmer with a more attractive structure requiring 1 kg/cm less force to shear, and was superior in organoleptic properties (overall 21% more desirable). Having 35 replicates to use for the data set, the results illustrated statistically significant variations in meat-quality traits and how they could be objectively measured. Nine months later, 12 of the students were surveyed. It was their perception that the laboratory was not any more effective than other laboratories in the same class, but they were able to remember 85% of the methods used to measure quality; about twice that of other methods taught in other laboratory sessions.     

Relationships between longissimus glycolytic potential and swine growth performance,carcass traits,and pork quality

The relationships between glycolytic potential and growth performance, carcass traits, and pork quality were investigated in a group of 72 pigs from the same genetic line. Glycolytic potential (GP) was determined on live-animal biopsy samples and postmortem samples taken from the longissimus muscle, and free glucose concentration was measured on the exudate from the longissimus muscle taken postmortem. The mean live-animal and postmortem GP and free glucose values were 201.6 micromol/g (range = 113.8 to 301.1), 149.8 micromol/g (range = 91.0 to 270.5) and 110.1 mg/dL (range = 30.0 to 406.0), respectively. Correlations between live-animal and postmortem GP and free glucose ranged from 0.47 to 0.70; however, all three measures were weakly related to growth and carcass traits (r = 0.03 to -0.22; P > 0.05). Correlations of GP and free glucose values with fresh pork quality measurements were moderate (r = 0.23 [P < 0.05] to -0.63 [P < 0.001]). Regression analysis suggested that a one standard deviation increase in live-animal and postmortem GP and free glucose resulted in an increase in L* values (0.99, 1.32, and 2.05, respectively) and drip loss (0.85, 1.10, and 1.39 percentage units, respectively), as well as a decrease in ultimate pH (0.05, 0.11, and 0.16, respectively). Correlations between GP and cooking loss and tenderness and juiciness scores ranged between 0.16 (P > 0.05) to 0.34 (P < 0.01). Free glucose concentration showed no relationship (P > 0.05) with cooking loss, tenderness, and juiciness. Regression analysis suggested that a one standard deviation increase in live-animal and postmortem GP increased cooking loss (1.26% and 1.65%, respectively) and would improve taste panel tenderness (0.54 and 0.44, respectively) and juiciness (0.40 and 0.48, respectively) scores. Increasing GP and free glucose was also associated with decreased longissimus fat and protein, and increased moisture contents (r = 0.14 [P > 0.05] to -0.45 [P < 0.001]). Overall, relationships with fresh meat quality characteristics were stronger for free glucose values than either live-animal or postmortem GP. Results from this study indicate that decreasing longissimus GP and free glucose concentrations may improve pork color and water-holding capacity.     

X-ray diffraction measurements of postmortem changes in the myofilament lattice of pork

Postmortem changes in the lateral spacing between filaments of the longissimus muscle in pork were examined by small-angle x-ray diffraction. Samples that were fixed in glutaraldehyde as soon as they were collected showed a rapid decrease in filament spacing from 1 h to 3 h and then a further, slower decrease to 24 h. Samples that were examined immediately or were kept prior to examination in buffered Ringer's solutions at pH values similar to those expected in the carcass showed a rapid decrease in filament spacing from 1 h to 3 h and then little further change to 24 h. In contrast, samples taken at various times postmortem and stored in Ringer's solutions at pH 7.2 for several hours before examination showed little postmortem change in lattice spacing. Fixed samples showed similar changes to those of unfixed samples, but the lattice spacing always was less in fixed than in unfixed samples. These results support the classic theory that much of the water that may be lost by drip and evaporation from meat originates from the spaces between the filaments. The major factor that caused shrinkage of the filament lattice and loss of water from the fibrils was pH.     

Technical note: use of belt grill cookery and slice shear force for assessment of pork longissimus tenderness

The present experiments were conducted to determine whether improved beef longissimus shear force methodology could be used to assess pork longissimus tenderness. Specifically, three experiments were conducted to: 1) determine the effect of belt grill (BG) cookery on repeatability of pork longissimus Warner-Bratzler shear force (WBSF), 2) compare the correlation of WBSF and slice shear force (SSF) with trained sensory panel tenderness ratings, and 3) estimate the repeatability of pork longissimus SSF for chops cooked with a BG. In Exp. 1 and 2, the longissimus was removed from the left side of each carcass (Exp. 1, n = 25; Exp. 2, n = 23) at 1 d postmortem and immediately frozen to maximize variation in tenderness. In Exp. 1, chops were cooked with either open-hearth electric broilers (OH) or BG, and WBSF was measured. Percentage of cooking loss was lower (P < 0.001) and less variable for chops cooked with a BG (23.2%; SD = 1.7%) vs. OH (27.6%; SD = 3.0%). Estimates of the repeatability of WBSF were similar for chops cooked with OH (0.61) and BG (0.59). Although significant (P < 0.05), differences in WBSF (4.1 vs. 3.9 kg) between cooking methods accounted for less than 5% of the total variation in WBSF. In Exp. 2, the correlation of SSF (r = -0.72; P < 0.001) with trained sensory panel tenderness ratings was slightly stronger than the correlation of WBSF (r = -0.66; P < 0.001) with trained sensory panel tenderness ratings, indicating that the two methods had a similar ability to predict tenderness ratings. In Exp. 3, duplicate samples from 372 carcasses at 2 and 10 d postmortem were obtained, cooked with BG, and SSF was determined. The repeatability of SSF was 0.90, which is comparable to repeatability estimates for beef and lamb. Use of BG cookery and SSF could facilitate the collection of accurate pork longissimus tenderness data. Time and labor savings associated with BG cookery and the SSF technique should help to decrease research costs.     

Effect of stunning on pork muscle quality]

The following methods of insensitisation were tested for their effects on muscle pork quality: Electrocoma, 75 V, 15 sec; Electrocoma following intensive electrical stimulation and irritation of various parts of the animals's body, using the insensitising forceps; Dart gun insensitisation. Also tested was the action of muscle relaxants on pork quality. Minor deviation from proper practice of electrical insensitisation was found to cause no significant deterioration in cutlet muscle and ham muscle quality. However, intensive irritation immediately before insensitisation caused higher percentages of PSE (16.7 per cent) and DFD (16.7 per cent). Dart gun insensitisation was quite often followed by poorer quality in the form of watery and bright pork (25.0 per cent). This had detrimental consequences for boiled ham processing (higher loss rates). Sensorial assessment of boiled ham obtained from animals in various categories did not reveal any significant discrepancy between the above techniques. When muscle relaxants were used, muscle pork quality of pigs relaxed by means of succicholine dichloride was much better than that in animals to which electrical insensitisation had been applied. Characteristics of such better quality included slower decline in pH over 45 minutes after death and lower drip loss.     

Measurement of the gristle content in beef by macroscopic ultraviolet fluorimetry

Ultraviolet light (365 nm) was directed at an angle of 45 degrees onto meat samples in a circular aperture (3 cm diameter). Fluorescence emissions were measured with a monochromator and a photomultiplier tube. Intact tendons and elastic ligaments had a strong fluorescence emission peak around 440 to 450 nm and only weak fluorescence around 510 nm. Tissues such as lean meat and adipose tissue that contain a matrix of reticular fibers (Type III collagen) had very low fluorescence around 440 to 450 nm so that their peak emittance was the weak fluorescence peak at 510 nm. The 510/440 nm ratio of fluorescence emissions was measured in comminuted meat samples containing varying mixtures of lean meat and gristle and varying mixtures of muscles with a high and low gristle content. The 510/440 nm ratio was correlated with the ratio of lean meat/gristle (r = .96, P less than .005). The 510/440 nm ratio was correlated with the ratio of longissimus/shank meat (two trials; r = .93, P less than .01; and r = .94, P less than .005). Results were only slightly changed when samples had dry surfaces or when samples were mixed with adipose particles. The relationship between the area of gristle in the samples and the 510/440 nm ratio was curvilinear with the greatest sensitivity to the fewest gristle fragments.     

Genetic analyses of growth, real-time ultrasound, carcass, and pork quality traits in Duroc and Landrace pigs: II. Heritabilities and correlations.

Knowledge of the genetic control of pork quality traits and relationships among pork quality, growth, and carcass characteristics is required for American swine populations. Data from a 2 x 2 diallel mating system involving Landrace and Duroc pigs were used to estimate heritabilities and genetic correlations among growth (ADG), real-time ultrasonic (US) measures of backfat thickness (BF) and longissimus muscle area (LMA), carcass characteristics, and various pork quality traits. Data were collected from 5,649 pigs, 960 carcasses, and 792 loin chops representing 65, 49, and 49 sires, respectively. Genetic parameters were estimated by REML assuming animal models. Heritability estimates were moderate to high for ADG, USBF, USLMA, carcass BF, and LMA, percentage of LM lipid (IMF), pork tenderness, and overall acceptability. Estimates were low to moderate for percentage of cooking loss, pH, shear force, percentage of LM water, water-holding capacity (WHC), pork flavor, and juiciness. Genetic correlations between US and carcass measures of BF and LMA indicate that selection based on US data will result in effective improvement in carcass characteristics. Selection for increased LMA and(or) decreased BF using US is, however, expected to result in decreased IMF and WHC, increased percentage of LM water and shear value, and in decreased juiciness, tenderness, and pork flavor. Average daily gain was favorably correlated with IMF and unfavorably correlated with shear force. Selection for increased ADG is expected to improve WHC but to decrease the percentage of LM water, with an associated decrease in juiciness. The results of this study suggest the feasibility of including meat quality in selection objectives to improve product quality. Favorable genetic correlations between IMF and eating quality traits suggest the possible merit of including IMF in the selection objective to improve, or restrict change in, pork eating quality.     

Preslaughter handling effects on pork quality and glycolytic potential in two muscles differing in fiber type composition

The objective of the present experiment was to investigate the effects of transportation, lairage, and preslaughter stressor treatment on glycolytic potential and pork quality of the glycolytic longissimus and the oxidative supraspinatus (SSP) or serratus ventralis (SV) muscles. In a 2 x 2 x 2 factorial design, 384 pigs were assigned randomly either to short (50 min) and smooth or long (3 h) and rough transport, long (3 h) or short (< 45 min) lairage, and minimal or high preslaughter stress. Muscle samples were taken from the LM at 135 min and from the SSP at 160 min postmortem for determination of the glycolytic potential and rate of glycolysis. At 23 h postmortem, pork quality was assessed in the LM and the SV. Effects of transport and lairage conditions were similar in both muscle types. Long transport increased (P < 0.01) the glycolytic potential and muscle lactate concentrations compared with short transport. Both long transportation and short lairage decreased (P < 0.01) redness (a* values) and yellowness (b* values) of the LM and SV. In combination with short lairage, long transport decreased (P < 0.05) pork lightness (lower L* values), and electrical conductivity was increased (P < 0.05) after long transport. Several interactions between stress level and muscle type (P < 0.001) were observed. High preslaughter stress decreased (P < 0.001) muscle glycogen in both the LM and SSP, but this decrease was greater in the LM. Lactate concentrations were increased (P < 0.001) only in the LM by high preslaughter stress. Increases in ultimate pH (P < 0.001) and decreases in a* values (P < 0.01) were greatest in the SV, whereas increases in electrical conductivity (P < 0.001) were greatest in the LM. The lack of interactions among transportation, lairage, and muscle type was attributed to the relatively minor differences in stress among treatments. It was concluded that, in glycolytic muscle types such as the LM, the high physical and psychological stress levels associated with stress in the immediate preslaughter period have a greater effect on the water-holding capacity of the meat and may promote PSE development. Conversely, oxidative muscle types tend to have higher ultimate pH values and produce DFD pork in response to intense physical activity and/or high psychological stress levels preslaughter.     

Relationships among glycolytic potential,dark cutting (dark,firm, and dry) beef,and cooked beef palatability

One hundred beef carcasses were selected at three packing plants and were used to determine the relationship between glycolytic potential (GP) and dark, firm, and dry (DFD) beef and to determine the effects of DFD status and GP on cooked beef palatability. Eight individual muscles were excised from one hindquarter of each carcass at d 7 postmortem: longissimus lumborum, psoas major, gluteus medius, tensor fasciae latae, rectus femoris, semimembranosus, biceps femoris, and semitendinosus. Ultimate pH, colorimeter readings, and Warner-Bratzler shear force were determined for all eight muscles at d 7 postmortem. A nine-member trained sensory panel evaluated cooked longissimus lumborum, gluteus medius, and semimembranosus steaks. Traits determined solely for the longissimus lumborum were GP (2 x [glycogen + glucose + glucose-6-phosphate] + lactate) and ether-extractable fat. A curvilinear relationship existed between GP and ultimate pH within the longissimus muscle. There appeared to be a GP threshold at approximately 100 micromol/g, below which lower GP was associated with higher ultimate pH and above which GP had no effect on ultimate pH. The greatest pH and muscle color differences between normal and DFD carcasses were observed in the longissimus lumborum, gluteus medius, semimembranosus, and semitendinosus muscles. Cooked longissimus from DFD carcasses had higher shear force values (46% greater) and more shear force variation (2.3 times greater variation) than those from normal carcasses. Dark cutting carcasses also had higher shear force values for gluteus medius (33% greater) and semimembranosus (36% greater) than normal carcasses. Sensory panel tenderness of longissimus, gluteus medius, and semimembranosus was lower for DFD carcasses than for normal carcasses. Longissimus and gluteus medius flavor desirability scores were lower for DFD than for normal carcasses. Steaks from DFD carcasses had more off-flavor comments than steaks from normal carcasses, specifically more "peanutty," "sour," and "bitter" flavors. The DFD effect of higher shear force values was approximately five times greater (+3.11 kg vs +0.63 kg) for carcasses with "slight" marbling scores than for carcasses with "small" marbling scores. In general, higher GP was associated with increased tenderness, even among normal carcasses. In conclusion, low GP was associated with DFD beef and resulted in substantially less-palatable cooked steaks.     

Optimal lairage times and conditions for slaughter pigs: a review

Keeping pigs in lairage provides a buffer to supply the slaughter line and allows the pigs to recover from the stress of transport. It has implications for the pigs' welfare by influencing their behaviour and ease of handling. In terms of pork quality, optimal lairage times for most pigs in the UK are probably one to three hours. Shorter lairage times are associated with more pale, soft, exudative (PSE) meat and longer times are associated with more dark, firm, dry (DFD) meat, more skin blemishes caused by fighting, and a lower carcase yield. However, when pigs have not been previously stressed by handling procedures, resting them in lairage may have no beneficial effects on the pigs' welfare or meat quality. At very high environmental temperatures there is evidence that a holding period of less than one hour may help to reduce the number of PSE carcases. At temperatures above 10 degrees C showering the pigs with water is beneficial. Fasting times need to be controlled to minimise the potential loss of carcase yield while reducing the volume of gut contents to reduce the risk of carcase contamination. Lairages can act as reservoirs of infection by pathogenic bacteria and there is evidence that longer holding times increase the risk of cross-contamination.     

Effects of dietary magnesium and short-duration transportation on stress response, postmortem muscle metabolism, and meat quality of finishing swine

Crossbred pigs, heterozygous for the halothane gene, were used to determine the effects of long-term dietary supplementation of magnesium mica (MM) and short-duration transportation stress on performance, stress response, postmortem metabolism, and pork quality. Pigs were blocked by weight, penned in groups (six pigs per pen), and pens (three pens per diet) were assigned randomly either to a control corn-soybean meal diet or the control diet supplemented with 2.5% MM (as-fed basis; supplemented at the expense of corn). Diets were fed during the early-finisher (0.95% lysine, as-fed basis; 43.7 to 68 kg) and late-finisher (0.85% lysine, as-fed basis; 68 to 103 kg) periods. At the conclusion of the 71-d feeding trial, 12 pigs from each dietary treatment were selected randomly and subjected either to no stress (NS) or 3 h of transportation stress (TS). Dietary MM had no effect (P > or = 0.40) on ADG or ADFI; however, G:F was improved (P < 0.05) during the early-finisher period when pigs were fed MM-supplemented diets. Plasma glucose concentrations were increased in TS pigs fed the control diet, but transportation did not affect plasma glucose in pigs fed 2.5% MM (diet x transportation stress; P = 0.02). Dietary MM did not affect blood lactate, cortisol, insulin, NEFA, Ca, or Mg concentrations in response to TS (diet x transportation stress; P > or = 0.13); however, circulating lactate, cortisol, and glucose concentrations increased in TS pigs (transportation stress x time; P < 0.01). The LM from TS pigs fed MM had higher initial (0-min) and 45-min pH values than the LM from NS pigs fed the control diet (diet x transportation stress x time; P = 0.07). Lactic acid concentration and glycolytic potential were greater in the LM of TS pigs fed MM than TS pigs fed control diets (diet x transportation stress; P < or = 0.01). Although some trends were identified, neither MM (P > or = 0.15) nor TS (P > or = 0.11) altered the color or water-holding capacity of the LM and semimembranosus. The transportation model elicited the expected changes in endocrine and blood metabolites, but dietary MM did not alter the stress response in pigs. Conversely, although pork quality traits were not improved by dietary MM, delaying postmortem glycolysis and elevating 0- and 45-min muscle pH by feeding finishing diets fortified with MM may benefit the pork industry by decreasing the incidence of PSE pork in pigs subjected to short-duration, routine stressors.     

Differences in calpain system,desmin degradation and water holding capacity between commercial Meishan and Duroc × Landrace × Yorkshire crossbred pork

The objective of this study was to examine the differences in calpain system, desmin degradation, pH values and water holding capacity (WHC) between muscles of commercial Meishan and Duroc × Landrace × Yorkshire crossbred pigs. Meishan pork presented better WHC evidenced by lower purge loss at days 1 and 3 and less centrifugation loss at day 1 post mortem (P < 0.05). pH values at 45 min post mortem in Meishan pork were significantly higher compared to crossbred pork (P < 0.05). Calpain‐1 messenger RNA (mRNA) expression was lower in Meishan pork compared to that from crossbred pork (P < 0.05). Additionally, calpain‐1 activity, the ratio of calpain‐1 to calpastatin activity and desmin degradation were lower in Meishan pork compared to those from crossbred pork samples (P < 0.05). The results indicate that the calpain system including mRNA expression and activity were different between commercial Meishan and crossbred pork resulting in difference in the degree of desmin degradation during post mortem aging. pH values at 45 min and 24 h post mortem rather than calpain activity and desmin degradation could explain the higher water holding capacity in commercial Meishan pork.     

Effect of dietary alpha-lipoic acid on growth, body composition, muscle pH, and AMP-activated protein kinase phosphorylation in mice

The effects of alpha-lipoic acid (ALA) on the growth, body composition, postmortem AMP-activated protein kinase (AMPK) activation, and 24-h muscle pH were investigated. Thirty male C57BL/6J mice were fed diets containing 0, 0.5, or 1.0% ALA (DM basis). At the end of the 3-wk feeding trial, carcass weights decreased (P < 0.05) 14 and 30% for mice fed 0.5 and 1.0% ALA, respectively, compared with the 0% group, with decreases in BW as the levels of dietary ALA increased. This change in carcass weight occurred because carcass fat content for mice receiving 0.5 and 1.0% ALA was 7.32 and 8.09% lower (P < 0.05), respectively, than for the 0% ALA treatment, and because gonadal fat decreased (P < 0.05) 85% in mice fed 1.0% ALA compared with those fed 0% ALA. Dietary ALA caused a slight increase (P < 0.05) in carcass moisture content, with no (P = 0.07) effect on protein and ash content. Furthermore, ALA supplement decreased (P < 0.05) ADFI (DM basis) from 4.3 g/d for 0% ALA-fed mice to 3.4 g/d for 1.0% ALA-fed mice. At 20 min postmortem, pH was greater (P < 0.05) in muscle of mice fed 1.0% ALA than in muscle of mice fed 0% ALA. Ultimate (24-h) pH values differed (P < 0.05) among treatments, and mean values were 5.83, 6.08, and 6.29 for 0, 0.5, and 1.0% ALA, respectively. Phosphorylation of AMPK alpha subunit at Thr172, an indicator of AMPK activation, was decreased (P < 0.05) in muscle of ALA-treated mice at 20 min postmortem. Because AMPK has a crucial role in the control of glycolysis, the reduction in AMPK activation decreases glycolysis, and thereby increases the ultimate pH of postmortem muscle. In summary, dietary ALA supplement can decrease fat accumulation in mice, and because ALA increased muscle pH at 20 min and 24 h postmortem, these results suggest that dietary ALA supplementation might decrease carcass fatness and prevent the development of PSE pork and poultry. However, further research is required to test the effects of ALA in swine and poultry.     

The halothane gene, energy metabolism, adenosine monophosphate-activated protein kinase, and glycolysis in postmortem pig longissimus dorsi muscle

The presence of the halothane gene results in PSE meat. However, the exact mechanisms linking the halothane gene and the incidence of PSE meat remain unclear. We hypothesize that the presence of the halothane gene accelerates energy consumption in postmortem muscle, which activates adenosine monophosphate-activated protein kinase (AMPK), leading to enhanced glycolysis and PSE meat. To test our hypothesis, energy status, AMPK activity, and glycolysis in the postmortem LM of the halothane gene carrier and halothane-negative pigs were compared. The results showed that the presence of the halothane gene accelerated energy depletion in postmortem muscle immediately after exsanguination, leading to rapid and early depletion of ATP, as shown by an increase in the (adenosine monophosphate + inosine monophosphate):ATP ratio in postmortem LM. In addition, an early AMPK activation was observed in LM from halothane carriers. The fructose-2,6-diphosphate concentration in postmortem LM was well correlated with AMPK activation. To be a potent stimulator of phosphofructose kinase, the increase in fructose-2,6-diphosphate is expected to activate phosphofructose kinase, a key enzyme controlling glycolysis, leading to enhanced glycolysis and early accumulation of lactic acid. In summary, this study showed that the presence of the halothane gene induced early energy depletion, which could be a primary reason causing AMPK activation, leading to accelerated glycolysis and an increased incidence of PSE meat. However, AMPK might also be activated by other mechanisms besides energy depletion, which warrants further studies.