Association of blood glucose,blood lactate,serum cortisol levels,muscle metabolites,muscle fiber type composition,and pork quality traits

The objective of this study was to investigate the relationship of blood glucose levels with blood lactate, serum cortisol levels, postmortem muscle glycogen and lactate content, muscle fiber type composition, and pork quality traits. Compared to pigs with lower blood glucose levels, pigs with higher blood glucose levels showed higher blood lactate and serum cortisol levels at exsanguination, and they had lower residual glycogen and higher lactate content in the muscle at 45 min postmortem. In addition, pigs with higher blood glucose levels had higher type IIB and lower type I area composition and finally exhibited lower muscle pH, paler color, and excessive loss of fluid on surface. These results imply that measuring blood glucose levels at exsanguination can be useful to indicate early glycolytic rates during postmortem and thus may be of value in the identification of pork with undesirable quality traits.     

The relation between glycogen, lactate content and muscle fiber type composition, and their influence on postmortem glycolytic rate and pork quality

This study examined the relation between glycogen, lactate content and muscle fiber type composition, and evaluated their influence on postmortem glycolytic rate and meat quality. Muscle samples were classified based on their glycogen and lactate content at 45 min postmortem. Muscles with low glycogen and high lactate levels showed low muscle pH_45 min and high R-values. However, muscles with low glycogen and lactate levels showed normal rates of postmortem glycolysis and normal meat quality. On the other hand, muscles with high glycogen and lactate content showed rapid postmortem glycolysis, paler surface color, higher drip loss, and higher extents of protein denaturation than muscles with high glycogen and low lactate content. These results may be partially explained by muscle fiber type composition. Muscles with low glycogen and lactate content at early postmortem are composed of significantly higher fiber type I and lower fiber type IIB as compared to muscles with high glycogen and lactate content.     

The influence of pork quality traits and muscle fiber characteristics on the eating quality of pork from various breeds

The purpose of this study was to compare parameters associated with pork quality, muscle fiber, and eating quality among various breeds, and to examine if differences in eating quality were associated to pork quality and muscle fiber characteristics. For carcass and pork quality, although there were significant differences among breeds, the values of parameters in all pigs were assigned a normal quality class, a likely outcome of the similarity in the area percentage of type I and IIB fibers. For eating quality, pork loins from Berkshire pigs were more tender and full of pork flavor than Landrace and Yorkshire pigs. Except juiciness and mouth coating, over 20% of the variability in the eating quality parameters can be explained by pork quality traits and muscle fiber characteristics using multiple regression analysis. Furthermore, differences in muscle pH_24 h, cooking loss, shear force, and NPPC marbling score could explain a large proportion of variation in eating quality parameters associated with the texture of pork.     

Effects of muscle cortisol concentration on muscle fiber characteristics, pork quality, and sensory quality of cooked pork

The effect of muscle cortisol concentration on muscle fiber characteristics and technological and sensory quality of pork was investigated. With the exception of the percentage of type IIA fibers, muscle fiber characteristics were not associated to cortisol levels. However, muscle cortisol concentration was positively associated with muscle pH(24h) (r = 0.23, P<0.05) and negatively associated with drip loss (r = -0.49, P<0.001), lightness (r = -0.24, P<0.05), shear force (r = -0.25, P<0.05), and texture profile analysis-hardness (r = -0.35, P<0.01). Additionally, the water-holding capacity of meat samples was affected by cortisol levels, with lower cortisol concentrations associated with less tender samples. These results indicate that the concentration of cortisol in the muscle is related with meat quality as well as the sensory quality of cooked pork.     

Control of fresh meat quality through manipulation of muscle fiber characteristics

Variations of fresh meat quality exist because the quality traits are affected by various intrinsic and extrinsic factors. Because the meat quality is basically dependent on muscle fiber characteristics, numerous studies have reported the relationship between quality traits and fiber characteristics. Despite intensive research, the relationship is yet to be fully established, however, the present knowledge suggests several potential ways to manipulate muscle fiber characteristics to improve meat quality. The present paper reviews the definition of fresh meat quality, meat quality traits and variations of meat quality. Also, this review presents recent knowledge underlying the relationship between fresh meat quality traits and muscle fiber characteristics. Finally, the present work proposes several potential factors including breed, genotype, sex, hormone, growth performance, diet, muscle location, exercise and ambient temperature that can be used to manipulate muscle fiber characteristics and subsequently meat quality in animals.     

Comparing the histochemical characteristics and meat quality traits of different pig breeds

The purpose of this study was to compare the muscle histochemical characteristics and meat quality traits between Berkshire, Landrace, Yorkshire, and crossbred pigs. A total of 594 pigs were evaluated. A clear difference between histochemical properties was observed from the results for fiber type composition. In Berkshire pigs, the area percentage of type I fibers was higher (P < 0.001) and that of type IIb fibers was lower (P < 0.05) than those of other breeds. The muscle pH_45min and pH_24h were significantly higher in Berkshire pigs. Drip loss and color parameters were significantly different between the breeds (P < 0.001). The Berkshire pigs, which showed the highest muscle pH and lowest drip loss and L^* values, contained a significantly higher percentage of type I fibers than the other breeds. By comparing the fiber type compositions of the different breeds, the results imply that the longissimus dorsi muscle of Berkshire pigs is more oxidative than that of other breeds. A high pH value in Berkshire pigs is due to a high percentage of type I fibers and a low percentage of type IIb fibers. Based on these results, we conclude that muscle fiber composition can explain in parts the variation of meat quality across and within breeds.     

The influence of fiber size distribution of type IIB on carcass traits and meat quality in pigs

The effects of detailed characteristics such as the size and proportion of type IIB fibers in longissimus thoracis muscle on carcass traits and pork quality were investigated. A total of 96 pigs were classified into four groups by the proportion of different IIB fiber sizes. Group NS (high proportion of both small- and normal-sized IIB fibers) had a higher total number (136.4) and density (231.31) of type IIB fibers, backfat thickness (37.20 mm) and intramuscular fat content (4.77%) than the other groups (P < 0.05), whereas Group NS had the lowest values of cross-sectional area (3413.85 μm²) and diameter (60.15 μm) of type IIB fiber among the groups (P < 0.05). Pig muscles with higher percentage of large IIB fibers exhibit tougher, lighter and more exudative meat than pig muscles with a higher proportion of small- or normal-sized IIB fibers. Therefore, an increase in the proportion of large IIB fibers causes poor quality of pork.     

The relationship between muscle fiber characteristics and meat quality traits of highly marbled Hanwoo (Korean native cattle) steers

To investigate the relationships between muscle fiber characteristics and meat quality traits of Korean native cattle, Hanwoo, Longissimus dorsi (LD), Psoas major (PM) and Semimembranosus (SM) muscles obtained from 18 Hanwoo steers and the muscle fiber characteristics were measured by histochemical analysis. Fiber number, area percentages and density of type IIA and IIB were lower in SM muscle, but higher in PM muscle than other muscles. LD muscle had higher pH_24h, L^? value and fat content whereas SM muscle had lower L^? value and fat content. The lowest WBSF with longer sarcomere length was observed in PM muscle, while SM muscle showed the highest WBSF with shorter sarcomere length. Consequently, the percentage of type I and IIB were highly correlated with meat quality traits and inversely correlated with fat content, L^? value and WBSF. Fiber number and area percentage of type I had a positive correlation with fat content and L^? value and a negative correlation with WBSF. These results suggest that Hanwoo steers had high marbling, more lightness and tenderness when the percentage of type I was high and the percentage of type IIB was low in muscle.     

Sensory evaluations of porcine longissimus dorsi muscle: Relationships with postmortem meat quality traits and muscle fiber characteristics

The objective of this study was to investigate sensory evaluations and their relationships with meat quality measurements and histochemical characteristics in both fresh and cooked pork. Based on the results, postmortem meat quality traits were closely related to almost all the evaluated sensory attributes. With regard to histochemical characteristics, muscle fiber area was related to both fresh- (r = 0.18, P < 0.05) and cooked-meat color (r = −0.24, P < 0.01) as well as abnormal flavor intensity (r = 0.25, P < 0.01), and muscle fiber composition was associated with fresh pork color and taste acceptability after cooking. There were no significant relationships (P > 0.05) between type IIa muscle fiber content and the evaluated sensory attributes; however, good meat sensory quality was partially explained by the percentage of type I fiber.     

Skeletal muscle fiber type and myofibrillar proteins in relation to meat quality

Although numerous studies have reported the relationships among muscle fiber characteristics, lean meat content and meat quality, controversial perspectives still remain. Conventional histochemical classifications may be involved in a high level of error, subjectivity and it could not clearly explain variety of myofibrillar protein isoforms. Therefore, more information is needed on how different factors, such as species, breeds, gender, nutrient conditions, physiological state of animals, and environment factors, affect ultimate meat quality in order to evaluate these uncertainness. Unfortunately, there is little information that completely covers with relationship among the muscle fiber types, myofibrillar proteins and enzymatic proteolysis. In addition to the perspective of postmortem metabolism, protein quality control in skeletal muscle and proteolytic degradation of muscle proteins during postmortem period could help to clarify this relationship. Therefore, the present review will focus on muscle fiber types, typing methods, muscle proteins and meat quality, and will summarize aspects of enzymatic view of proteasome.     

Influence of myosin heavy- and light chain isoforms on early postmortem glycolytic rate and pork quality

This study addressed the influence of the content of myosin heavy- (MHC) and light chain (MLC) isoforms on early postmortem glycolytic rate and meat quality traits in the porcine longissimus muscle. The fast-glycolysing group showed lower contents of MHC slow and MLC 1s isoforms (P<0.05), and higher MHC fast isoform contents than the normal-glycolysing group (P<0.05). The MHC fast/slow ratio was correlated with lactate content (r=0.41) and early postmortem muscle pH (r=-0.51), and the content of the MLC 1s isoform was negatively correlated with lactate content and glycolytic potential (r=-0.38 and -0.36, respectively). Hence, both the MHC and MLC isoforms did influence metabolite contents, thus also affecting glycolytic rate, and suggested that the myosin isoforms, in particular the MHC isoforms, might also have some bearing on the extent of protein denaturation and pork quality during the early postmortem period.     

Correlations of trained panel sensory values of cooked pork with fatty acid composition,muscle fiber type,and pork quality characteristics in Berkshire pigs

The objective was to examine the relationship of trained panel sensory scores of cooked pork with fatty acid composition, muscle fiber type, and meat quality characteristics from Berkshire pigs. No or few associations were found between the panel sensory scores of cooked meat, especially tenderness attributes, and fatty acid composition; however, intramuscular fat content positively correlated with off-flavor score (r = 0.31). On the other hand, the morphological characteristics of muscle fibers were correlated with panel sensory values. Muscles with smaller cross-sectional area and higher density of fibers were more closely associated with softer, more tender panel scores and a lower number of chews than muscles with larger fiber area and lower density of fibers. The water holding capacity test of filter-paper fluid uptake was moderately correlated with panel scores of softness (r = 0.33), initial tenderness (r = 0.38), chewiness (r = 0.40), juiciness (r = − 0.27), flavor intensity (r = − 0.23), and off-flavor (r = 0.30). Panel sensory values of Berkshire pig meat was moderately related to postmortem meat quality, especially water holding capacity. A more thorough understanding of the relationships between fatty acid composition and muscle fiber type with palatability is needed.     

Heterocyclic amines in aged and thermally treated pork longissimus dorsi muscle of normal and PSE quality

Here we have studied the effects of ageing time (as non-aged, 24 h post mortem vs. aged, 3, 6 and 10 days post mortem, kept at 2 °C), muscle quality (normal vs. pale, soft and exudative [PSE]) and internal cooking temperature (T_i, 70 and 95 °C) on the content of HAs in grilled steaks. HA precursors (creatine, creatinine, free amino acids, monosaccharides), ageing, and the muscle quality indicators of drip loss, instrumentally measured colour, pH, non-protein nitrogen, and grilled-meat WBSF of the pork longissimus dorsi muscle were determined. In general, all of the ageing and muscle quality indicators and precursors of the HAs were influenced by ageing time. Creatine content decreased significantly, and creatinine increased with days of ageing, dependent on muscle quality. There was higher content of total free amino acids after 10 days of storage, as compared to non-aged pork. A higher level of free amino acids was seen in normal as compared to PSE pork muscle. The glucose content increased with ageing, and there was a higher glucose content in PSE as compared to normal muscle. Five specific HAs were measured: PhIP, MeIQx, DiMeIQx, Harman and Norharman. The total HA content increased with ageing (non-aged and normal pork HA content, 1.35 ng g⁻¹; after 3 days, 1.38 ng g⁻¹; after 6 days, 1.77 ng g⁻¹; and after 10 days, 3.49 ng g⁻¹) and it was dependent on the internal temperature; greater amounts of HAs were formed in samples grilled to T_i = 95 °C, than in samples grilled to T_i = 70 °C (8.34 vs. 2.36 ng g⁻¹). No marked differences due to muscle quality were seen in HA content at T_i = 70 °C (with the exception of MeIQx). The mean HA content of PSE samples grilled to T_i = 95 °C was 22% more than for the normal samples.     

Effects of variation in porcine MYOD1 gene on muscle fiber characteristics, lean meat production, and meat quality traits

Three single nucleotide polymorphisms (SNPs) in the porcine MYOD1 gene were used for association analysis and haplotype construction to evaluate the effects of their substitution. Four hundred and three pigs of Yorkshire and Berkshire breeds were used. The mRNA expression levels of MYOD1 were examined. The g.489C>T and g.1264C>A SNPs were significantly associated with several muscle fiber characteristics, the loin eye area, and lightness. Particularly, animals having hetero-genotypes of both sites showed good performance both in lean meat production and meat quality traits. The results of haplotype substitution were similar to the associations of individual SNPs. Moreover, the 2 SNPs had significant effects on mRNA expression. Therefore, the g.489C>T and g.1264C>A SNPs in MYOD1 may be meaningful DNA markers that can be used for improving important porcine economic traits.     

Strategic finishing feeding as a tool in the control of pork quality

A standard diet and two finishing feeding strategies known to reduce muscle glycogen stores were investigated in combination with exercise immediately prior to slaughter in pigs. The objective was to determine the influence of muscle glycogen at slaughter on temperature and pH in post-mortem muscle, the colour, drip loss and Warner–Bratzler shear force of the meat. The muscle glycogen stores were reduced by strategic finishing feeding. In general, pH_{45 min} was higher in muscles from strategically fed pigs compared with control pigs. Exercise also resulted in higher pH_{45 min} in control pigs compared to non-exercised control pigs, while the opposite was seen in muscles from strategically fed pigs. Exercise resulted in higher muscle temperatures in the carcasses irrespective of feeding strategy. pH_{24 h} were higher in M. biceps femoris and M. semimembranosus from exercised, strategically fed pigs compared with the corresponding controls. In contrast, irrespective of feeding strategy no difference in pH_{24 h} was registered in the meat of non-exercised pigs. Drip loss was lower in meat of strategically fed pigs compared with meat of control pigs. Moreover the drip loss was lowest in the meat of non-exercised pigs. The present study shows that strategic finishing feeding has high potential for the control of pork quality.     

Manipulation of critical quality indicators and attributes in pork through vitamin E supplementation, muscle glycogen reducing finishing feeding and pre-slaughter stress

The combination of a muscle glycogen reducing diet or a standard diet (control group) with normal (80 mg/kg) and high vitamin E levels (500 mg/kg) and exercise immediately prior to slaughter was used on 56 pigs to investigate the influence on meat quality indicators (pH and temperature) and attributes (drip loss, colour and Warner–Bratzler shear force). The drip loss was reduced in M. longissimus dorsi, M. biceps femoris and M. semimembranosus in pigs given the muscle glycogen reducing diet compared with the control groups, the greatest effect was seen in exercised pigs. These results can be explained by an early post mortem reduction in glycometabolism in pigs fed muscle glycogen reducing diets rather than by an increase in ultimate pH. Noticeably, high dietary vitamin E level increased muscle glycogen stores by about 10% on the day prior to slaughter but not on the day of slaughter in both dietary groups compared with the low dietary vitamin E level, which in fact reduced rather than improved the water-holding capacity, especially in pigs fed the standard diet.     

Effect of visual marbling on sensory properties and quality traits of pork loin

Pork loins (N = 53) were selected from a commercial packing plant to determine the influence of subjective marbling score on sensory attributes and eating quality properties. The pork loins were obtained from commercially raised hybrid barrows (average carcass weight = 67.7 kg), originating from nine cooperating herds, and fed similar diets throughout the finishing period. Carcass quality measurements, trained sensory panel analyses, fatty acid composition, thiobarbituric acid-reactive substance (TBARS) index, and cholesterol content were assessed and analyzed on the individual pork loins. With an increase in marbling level, there was a corresponding decrease in drip loss (P = 0.049) and observed increases in pH (P = 0.001), sensory tenderness (P = 0.001), and sensory juiciness scores (P = 0.017). The most notable results demonstrated that protein concentrations were reduced as marbling levels amplified (P = 0.012). The increase in marbling score was observed to be a significant source of variation in polyunsaturated fatty acid (PUFA) concentrations. Linoleic and arachidonic acids decreased in both raw and cooked samples as marbling score increased. The data demonstrated that visual marbling score does have an influence on sensory properties and pork quality.     

Trained sensory perception of pork eating quality as affected by fresh and cooked pork quality attributes and end-point cooked temperature

The present study evaluated individual and interactive influences of pork loin (n = 679) ultimate ph (pH), intramuscular fat (IMF), Minolta L∗ color (L∗), Warner-Bratzler shear force (WBSF), and internal cooked temperatures (62.8 °C, 68.3 °C, 73.9 °C, and 79.4 °C) on trained sensory perception of palatability. Logistical regression analyses were used, fitting sensory responses as dependent variables and quality and cooked temperature as independent variables, testing quadratic and interactive effects. Incremental increases in cooked temperature reduced sensory juiciness and tenderness scores by 3.8% and 0.9%, respectively, but did not influence sensory flavor or saltiness scores. An increase of 4.9 N in WBSF, from a base of 14.7 N (lowest) to 58.8 N (greatest) was associated with a 3.7% and 1.8% reduction in sensory tenderness and juiciness scores, respectively, with predicted sensory tenderness scores reduced by 3.55 units when comparing ends of the WBSF range. Modeled sensory responses for loins with pH of 5.40 and 5.60 had reduced tenderness, chewiness, and fat flavor ratings when compared with responses for loins with pH of 5.80 to 6.40, the range indicative of optimal sensory response. Loin IMF and L∗ were significant model effects; however, their influence on sensory attributes was small, with predicted mean sensory responses measurably improved only when comparing 6% and 1% IMF and L∗ values of 46.9 (dark) when compared with 65.0 (pale). Tenderness and juiciness scores, were related to a greater extent to loin WBSF and pH, and to a lesser extent to cooked temperature, IMF and L∗.     

Influence of meat exudates on the quality characteristics of fresh and freeze-thawed pork

The influence of the accumulated exudates released from pork loin of itself on the quality characteristics of fresh and freeze-thawed pork during cold storage was investigated. Pork loins were divided into four groups (fresh pork with exudates, fresh pork without exudates, freeze-thawed pork with exudates and freeze-thawed pork without exudates) and stored at 1.0 °C for 7 days. Exudate amount increased due to freeze-thawing and with storage, and most quality traits such as drip loss, cooking loss, tenderness, lightness, redness, and moisture content were affected by freeze-thawing (p < 0.05). Freeze–thaw increased drip loss but decreased moisture content, cooking loss, tenderness, lightness and redness of meat (p < 0.05). Microbial growth was solely affected by exudate removal and the removal of initial exudates decreased microbial growth (p < 0.05). Exudates were positively correlated with total protein content and total plate count but negatively correlated with pH and cooking loss. Therefore, removing meat exudates and avoiding freeze can slow down the quality deterioration of pork during cold storage.     

The relationship between exsanguination blood lactate concentration and carcass quality in slaughter pigs

A group of 128 cross-bred barrows were used to determine the relationship between exsanguination blood lactate concentration ([LAC]) and carcass quality following commercial marketing conditions. After 10 h of feed withdrawal, pigs were loaded on a truck with a hydraulically lifted second deck and transported approximately 1 h to the slaughter facility. Pigs were rested for 8 h and stunned with carbon dioxide. Blood lactate concentration was measured on exsanguination blood. Fourteen pork quality measurements were obtained following normal post-mortem processing. Pearson correlations were used to determine the relationships between [LAC] and the meat quality parameters. Exsanguination blood lactate concentration ranged from 4 to 19.7 mM. Higher lactate was associated with lower 60 min pH (P = 0.0004) and higher drip loss (P = 0.02). These results suggest that under low-stress loading and standard marketing conditions, exsanguination [LAC] is predictive of the rate of early post-mortem metabolism.