The influence of myoglobin on the colour of minced pork loin

The influence of the total and chromatic absorbance at wavelengths of 525 nm (A₅₂₅ and A_525p) and 700 nm (A₇₀₀), and the relative content of oxymyoglobin (MbO₂), metmyoglobin (MetMb) and deoxymyoglobin (Mb), on the value of the colour parameters (L*, a*, b*, C* and h°) of minced pork loin, were evaluated. Lightness (L*) depended almost entirely on variation in total absorbance at a wavelength of 525 nm. Redness (a*) depended on the forms of myoglobin and A_525p, while yellowness (b*) depended mainly on the proportions of the reduced form (Mb), the oxygenated form (MbO₂) and the oxidised form (MetMb). Yellowness (b*) significantly increased with a decrease in the relative amount of Mb and an increase in relative amounts of MbO₂ and MetMb, although a greater impact was exerted by fluctuations in MbO₂ than MetMb. Variability of chroma (C*) depended mainly on proportions of the forms of myoglobin. Hue angle (h°) depended primarily on chromatic absorbance at 525 nm (A_525p).     

The significance of diet, slaughter weight and aging time on pork colour and colour stability

The objective of the present study was to investigate the effect of a diet with a low content of digestible starch, slaughter weight and subsequent aging time on meat colour and colour stability. Pork colour was determined as the extent of blooming of M. longissimus thoracis (LT) and M. semimembranosus (SM) after 1, 2, 4, 8 and 15 days postmortem and as colour stability during a subsequent storage period in air for 6 days. Compared to the control diet, the experimental diet resulted in a significantly lower postmortem muscle temperature (1°C; p<0.0001). Moreover, high slaughter weight (110kg) resulted in a higher postmortem temperature in LT (p<0.001) compared to low weight (85kg). Independent of feeding strategy and slaughter weight, the extent of blooming decreased during the first 2-4 days of aging in LT, however, the effect was more pronounced in meat from experimentally fed pigs and pigs with high slaughter weight. This effect was not seen in SM, where a gradual increase in blooming took place throughout the aging period. The colour stability was found to be superior in aged pork from experimentally fed pigs. The discoloration rate was faster in SM compared to LT. In conclusion, the present study shows that the diet composition can be used as a tool to control meat colour and colour stability in pork.     

Significance of storage time on degree of blooming and colour stability of pork loin from different crossbreeds

The objective was to investigate the effect of ageing time (1 day vs. 8 days postmortem) and sire breed used in the crossbreed (Duroc sired vs. Landrace sired pigs) on blooming ability and colour stability of pork M. longissimus dorsi (LD). The colour was measured during blooming (0, 10, 30, 60, 90 min and 24 h after cutting) and during subsequent display (1, 2, 3 and 6 days) at 3 °C. The contents of deoxymyoglobin (Mb), oxymyoglobin (MbO₂) and metmyoglobin (MetMb) were calculated. Ageing improved the blooming of LD from both crossbreeds with increased content of MbO₂ and decreased content of Mb, resulting in increased lightness, redness and yellowness. Ageing had smaller effect on colour stability with slightly lower MetMb in aged meat. Crossbreed affected both blooming and colour stability. LD from Landrace-sired pigs bloomed more than LD from Duroc-sired pigs, but more MetMb was formed during subsequent storage, although at a low level in both crossbreeds. The present data show superior colour characteristics of fresh pork aged for 8 days.     

Significance of early postmortem temperature and pH decline on colour characteristics of pork loin from different crossbreeds

The significance of early postmortem (pm) temperature and pH decline and the level of the muscle metabolites creatine phosphate (CP) and adenosine triphosphate (ATP) on the colour of porcine M. longissimus dorsi was studied in a factorially designed experiment. Two stress levels peri mortem (minimal stress vs treadmill exercise and electrical stunning of the pigs) and four genotypes (Duroc boars crossed with Landrace–Yorkshire sows vs. Hampshire–Duroc boars crossed with Landrace–Yorkshire sows, including carriers and non-carriers of the halothane and RN⁻ genes, respectively) were included. Early pm muscle temperature and the accompanying pH decline had a significant influence on the pork colour independent of genotype. The combination of high temperature and low pH early pm increased lightness and yellowness, which is ascribed to inactivation of oxygen-consuming enzymes and protein denaturation. The effect of early pm temperature and pH on pork redness was more complex. It appears to be closely related to the extent of heat generation, CP and ATP levels and pH immediately pm in the muscle, which influence the activity of oxygen-consuming enzymes.     

Influence of dietary creatine monohydrate and carcass cooling rate on colour characteristics of pork loin from different pure breeds

Increased creatine content in the muscle may delay postmortem (pm) lactate formation and postpone pH decline, hence potentially affect the colour of pork. The influence of dietary supplementation with 0 or 50 g creatine monohydrate (CMH)/d for 5 days prior to slaughter and two cooling rates of pig carcasses on the colour characteristics of pork loin from purebred Duroc and Landrace pigs was investigated. CMH increased the content of creatine phosphate in pork loin measured immediately following bleeding, delayed early pm pH decline and gave rise to less red and yellow colour, probably due to induction of a more pronounced oxidative muscle metabolism. A faster cooling rate pm induced darker and less yellow colour in loins from Duroc and Landrace pigs, while only loins from Landrace became less red. Loins from Duroc pigs were darker, less red and less yellow than loins from Landrace pigs, due to slower pH decline and a higher ultimate pH in these loins. Colour stability of pork loin during chill storage, measured as oxidation to metmyoglobin, was not affected by dietary CMH, cooling rate or pig breed. Consequently, the registered differences in colour between treatments during storage were merely due to the degree of initial blooming, and more attention to factors of importance for the degree of blooming should be in focus in future studies of factors of importance for meat colour.     

Evaluating an objective method to measure fresh pork loin firmness

The purpose of this study was to develop an objective method for measuring fresh pork loin firmness. A total of 42 fresh boneless pork loins were collected from a range of subjective firmness scores based on the whole boneless loin to create a population suitable for creating a prediction equation. Loins were subjectively scored by panelists prior to objectively being measured with a Texture Analyzer. An R(2) value of 0.54 was achieved for the prediction equation that was generated. A second trial was performed to test the equation resulting in an R(2) value of 0.30 concerning subjective and objective values. The results from these studies indicate that it is possible to create a standardized protocol in order to determine objective firmness that would be useful for future studies and for the development of hand held or online firmness measuring devices.     

Modelling quality variations in commercial Ontario pork production

This study explores the interactions of sensory and nutritional environment with genotype occurring in current commercial pork production in Ontario, Canada, which may interact to result in poor quality meat. The study focussed on identifying factors and signalling mechanisms that contribute to poor meat quality, in order to develop strategies to reduce the incidence of unacceptable product quality. In the first phase of the work reported here, animal behaviour and muscle metabolism studies were related to meat colour, tenderness and water-holding capacity measurements from commercially-produced pigs killed in a commercial packing plant. A partial least squares analysis was used to determine the most important of the principal production variables, peri-mortem biochemical measures and post-mortem carcass condition variables studied, in terms of their influence on water-holding, toughness and colour (L*-value). Variations between producer and kill day at the slaughterhouse were very strong contributors to variability in these three meat quality parameters, followed by pH variations. A second phase of the study is currently underway to characterize patterns of gene expression related to extremes of end-product quality and to reduce quality variations by nutritional and behavioural management strategies.     

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.     

Predicting Longissimusdorsi myoglobin oxidation in aged beef based on early post-mortem colour measurements on the carcass as a colour stability index

Sixty young bulls of the Pirenaica breed, representative of the beef production and marketing system in northern Spain, were used. The carcass grading and weight, pH at 24 h post-mortem, and objective colour measurements (CIE L^∗a^∗b^∗) were recorded on the Latissimus dorsi, Rectus abdominis and Longissimus dorsi in order to find indicators and predictors of beef colour stability (Longissimus dorsi metmyoglobin percentage on ageing for 3, 7 and 14 days) by means of early post-mortem measurements on the carcass.     

Effect of vacuum and modified atmosphere packaging on the quality of pork loin

The effect of packaging in protective atmospheres on the process of lipid oxidation, colour and water retention capacity of pork loin chops during refrigerated storage was investigated. The use of modified atmospheres with a high oxygen concentration (70%) acted as a pro-oxidation factor both for fatty acids and for cholesterol (an increase of 86.4% on the initial COPS content). No significant advantages were found in the use of these atmospheres concerning the colour of the meat. Vacuum packaging was seen to be an interesting alternative in the packaging of pork, due to the fact that it increases oxidative stability, which brings about greater colour stability and therefore increases the shelf life. The only disadvantage of this type of packaging is that it increases initial weight loss (5.1% on day 2 of storage).     

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.     

Pre-slaughter transport, AMP-activated protein kinase, glycolysis, and quality of pork loin

Numerous studies have revealed that pre-slaughter stress, like transport, increases the occurrence of pale, soft, and exudative (PSE) pork meat. The molecular mechanism underlying this phenomenon, however, is poorly defined. In this study, we investigated the effects of pre-slaughter transport and subsequent rest on energy metabolism, AMP-activated protein kinase (AMPK) activation, and glycolysis in postmortem pork loin. Results indicated that pre-slaughter transport accelerated ATP depletion, which led to lower energy status in postmortem muscle immediately post-exsanguination when compared with control. The lower energy status led to AMPK activation within 1h postmortem, subsequently increasing glycolysis, leading to rapid glycolysis and high incidence of PSE meat. Allowing pigs to rest after transport restored energy status in muscle ante-mortem. Higher energy status then prevented premature and rapid AMPK activation in postmortem muscle and lessened the negative effects of pre-slaughter transport on meat quality. AMPK regulated glycolysis in postmortem muscle, at least partially, through phosphorylation and activation of phosphofructose kinase-2, since fructose-2,6-diphosphate content, an allosteric activator of phosphofructose kinase-1, was well correlated with AMPK activation and glycolytic rate. This suggests that AMPK is a potential molecular target for the control of PSE incidence in pork.     

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∗.     

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.     

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.     

Effect of Duroc content, sex and ageing period on meat and eating quality attributes of pork loin

This study was conducted to determine the effect of percentage Duroc content of entire male and female pigs and ageing period on meat and eating quality attributes of pork loin (M. longissimus thoracis et lumborum). A total of 84 pigs [entire males (n=42) and female (n=42)] of 0% Duroc (100% Large White), 50% Duroc (Duroc×Large White) or 100% Duroc (n=14 pigs per sex×genotype combination) were slaughtered at a liveweight of 100 kg. Steaks from the M. longissimus lumborum of female pigs were aged for either 2 or 7 days post-slaughter and evaluated using a consumer taste panel. Eating quality attributes of tenderness, flavour and overall liking of pork loin steaks from female pigs were not (P>0.05) influenced by Duroc content. Pork from 100% Duroc pigs was juicier (P=0.05) and had a higher (1.84%, P=0.05) intramuscular fat content than pork from 0 and 50% Duroc pigs (1.40 and 1.25%, respectively). Pork from entire male pigs had a lower (P<0.001) intramuscular fat content, was darker (P<0.01) in colour and recorded higher (P<0.01) Warner Bratzler shear force values compared with pork from female carcasses. Ageing pork loin steaks in vacuum bags for 7 days improved tenderness (P<0.01), flavour (P<0.05) and overall liking (P<0.05) compared with steaks aged for 2 days post-slaughter. Ageing of pork steaks for 7 days post-slaughter improved eating quality attributes far more effectively than increasing percentage Duroc content of pigs, which only influenced consumer scores for juiciness.     

Effect of tiger nut fibre on quality characteristics of pork burger

Horchata is a refreshing beverage obtained from tiger nut tubers that yields high amount of by-products. These by-products have a high content of fibre that allows its application in the development of dietary fibre rich foods. The utilization of increasing levels (0%-control, 5%, 10% and 15%) of tiger nut fibre (TNF), in the formulation of pork burgers was evaluated. This evaluation was based on: chemical composition, physicochemical, cooking characteristics and sensory properties of burgers. Pork burgers elaborated with TNF had higher nutritional value (higher fibre content) and better cooking characteristics (higher cooking yield, fat retention and moisture retention) than control burgers. Some of the negative changes in colour (a* decrease and b* increase) and texture (chewiness and springiness increase) parameters due to TNF addition observed in raw burgers were masked by the stronger modifications due to the cooking process. Burgers with TNF were perceived as less greasy, less juicy, more grainy and with less meaty flavour than controls; although this perception did not reduce the overall acceptability of burgers. Overall acceptability scores were slightly lower in burgers with 15% TNF, although no significant differences were detected with the scores of control, 5% and 10% TNF burgers. TNF addition to burgers is a promising and convenient application as dietary fibre of burgers was significantly increased without changes in sensory acceptance.     

Deep freezing to maintain the freshness of pork loin during long-term storage

Food Science and Biotechnology - As storage temperature impacts frozen meat quality, we evaluated the ideal freezing and storage temperatures for pork loin, and effects of long-term storage...     

Impact of RN genotype and ageing time on colour characteristics of the pork muscles longissimus dorsi and semimembranosus

The effect of RN genotype on pH decline, ultimate pH, pigment content, blooming and colour stability during 6 days of display at 5 °C was studied in two pig muscles, M. longissimus dorsi (LD) and M. semimembranosus (SM), and furthermore the effect of anaerobic storage time (2 days vs. 9 days of ageing) on the same parameters was examined. The postmortem pH decline was faster and the ultimate pH lower in LD and SM of the RN⁻ genotype compared with corresponding muscles from the rn⁺ genotype. Pork of the RN⁻ genotype was initially lighter and more red and yellow than pork of the rn⁺ genotype due to a higher degree of blooming, which might be explained by the faster pH decline and/or lower ultimate pH. The level of oxymyoglobin (MbO₂) was decisive for the redness of both muscles during display in air despite a higher presence of metmyoglobin (MetMb). Pork of the RN⁻ genotype was thus redder than that of the rn⁺ genotype throughout display in air despite higher oxidation to MetMb. Ageing for 9 days in chill improved the blooming potential in pork of both genotypes compared with 2 days of ageing, resulting in superior meat colour. However, only in pork from the RN⁻ genotype, the colour was not negatively affected by ageing time upon display in air.     

The influence of RN genotype, including the new V199I allele, on the eating quality of pork loin

The eating quality of M. longissimus dorsi (LD) from RN⁻ homozygotes, RN⁻ heterozygotes and RN⁻ non-carriers was investigated in a Swedish Hampshire×Finnish Landrace pig population. The recently identified new allele (V199I, here denoted rn*) at the RN locus was also detected among the pigs selected and included in the sensory evaluation. The number of animals varied from 10 to 15 in the five genotype groups; RN⁻/RN⁻, RN⁻/rn+, RN⁻/rn*, rn+/rn+ and rn+/rn* (in total 59 pigs). In addition, one pig was determined to be rn*/rn* but was excluded from the analysis. The three genotypes in which the RN⁻ allele was represented (RN⁻/RN⁻, RN⁻/rn+ and RN⁻/rn*) had higher glycogen and lower protein contents as well as lower ultimate pH (measured 48 h post-mortem) in LD than the non-carriers (rn+/rn+ and rn+rn*). Of the sensory parameters evaluated (tenderness, chewing time, chewing residual, juiciness, meat flavour and acidity), the five RN genotypes only affected acidity significantly; the RN⁻ allele contributing to a more acid taste in LD. The influence of the rn* allele resembled that of rn+ on the sensory parameters. When the material was divided into three groups (homozygous, heterozygous and non-carriers of the RN⁻ allele) the juiciness was found to be significantly influenced by RN genotype, and LD from animals that were homozygous and heterozygous with respect to the RN⁻ allele exhibited a higher juiciness than LD from non-carriers. The RN⁻ allele also tended to contribute to greater tenderness, which was significantly higher in LD from heterozygous carriers than from non-carriers of the RN⁻ allele. A more rapid decline in pH (measured as pH at 45 min and 3 h post-mortem) contributed to a greater tenderness in LD (according to a trained panel and Warner-Bratzler shear force). In addition to the RN genotype, the decline in pH was influenced by carcass weight, which varied between 71 and 97 kg, and by stunning procedure, which changed during the course of the study from individual to group stunning with CO₂. The individual stunning procedure contributed to a lower pH in the initial post-mortem phase (pH₄₅), whereas a higher carcass weight and the RN⁻ allele lowered the pH in the mid-post-mortem region (pH_3h and pH_24h), significantly (P0.05). The pH continued to decline after 24 h post-mortem and the ultimate pH was not reached until 48 h post-mortem. The cooking loss, juiciness and acidity were related to the specific characteristics of the RN⁻ carriers, such as higher glycogen content, lower protein content and lower ultimate pH (pH_48h).