A second mutant allele (V199I) at the PRKAG3 (RN) locus- I. Effect on technological meat quality of pork loin

The effect of three alleles (RN(-), rn(+) and a second mutant allele V199I, denoted rn*) at the PRKAG3 (RN) locus on such meat quality traits as pH, internal reflectance (FOP), Warner-Bratzler shear force, water-holding capacity and cooking loss were studied. M. longissimus dorsi (LD) from a total of 334 crossbreed pigs, entire males and females, Hampshire (H) and Finnish Landrace (L) of three combinations H × LH, LH × H and LH × LH, were used. The PRKAG3 alleles were identified with a DNA test and all possible RN genotypes, RN(-)/RN(-) (23%), RN(-)/rn(+) (24%), RN(-)/rn* (33%), rn(+)/rn(+) (8%), rn(+)/rn* (9%) and rn*/rn* (2%), were found. Water, intramuscular fat, protein and glycogen contents were determined. All the three alleles at the RN locus affected the studied technological meat quality traits of pork loin, except for the internal reflectance 24 h post mortem and the shear force. The RN(-) allele was dominant over the other two alleles, rn(+) and rn*, in LD with regard to ultimate pH, water-holding capacity and cooking loss, giving lower ultimate pH and water-holding capacity and higher cooking loss. The rn* allele affected ultimate pH in LD of non-carriers of the RN(-) allele, giving higher ultimate pH. The RN(-) allele was also dominant over the other two alleles in residual glycogen content in entire male pigs, but not in female pigs, where the rn* allele had a glycogen-lowering effect. The water content was higher and the protein content lower in LD of all RN(-)/- animals compared with the other genotypes, while no significant differences were found with regard to IMF content. Water-holding capacity, cooking loss and shear force were higher in LD of entire males compared with females.     

Sensory quality and the incidence of PSE of pork in relation to crossbreed and RN phenotype

The effects of crossbreed and of RN phenotype on pork and its eating quality were evaluated in four different pig crossbreeds [involving Swedish Landrace (L) × Yorkshire (Y) sows and Hampshire (H), Duroc (D), Yorkshire (Y) or Hampshire × Yorkshire (HY) as the terminal sire]. Pigs from the LYH crossbreed were also classified as either carriers or non-carriers of the RN(-) allele. In the crossbreeds investigated, M. longissimus dorsi (LD) and M. semimembranosus (SM) from LYH were found to have the lowest pH as measured 24h post-mortem (pH(24h)). The low pH in the LYH crossbreed was due to the large proportion of RN(-) carriers it had (approximately 70%). The non-carriers of the RN(-) allele in the LYH crossbreed had a pH(24h) close to that of LYD, LYY and LYHY. In a selected group of pigs (N=50), the ultimate pH in the ham muscles M. biceps femoris (BF), M. quadriceps femoris (QF), M. gluteus medius (GM) and M. semitendinosus (ST) was also found to be lower in RN(-) carriers of LYH than in the other crossbreeds. As determined visually, LYD had the highest frequency (2%) of pale, soft and exudative meat (PSE), in LD. Ham from RN(-) carriers of LYH had the highest frequency (23%) of PSE meat around the femur, indicating that when the pH is low, the deep musculature, in which the chilling rate can be slow, is particularly sensitive to the development of PSE. According to assessments by members of a trained sensory panel, tenderness was significantly greater in LD from carriers of the RN(-) allele in LYH than in LD from LYD, LYHY and non-carriers of LYH. The tenderness of LD from LYY was rated as intermediate. The intramuscular fat content was found to be highest in LD from LYD, no relationship between intramuscular fat content and tenderness being found. The RN(-) carriers of LYH received the highest ratings in terms of juiciness. In conclusion, the sensory ratings demonstrated the great eating quality of LD from carriers of the RN(-) allele, indicating that abandoning the Hampshire crossbreed or eliminating the RN(-) allele from it, would result in the meat being less tender.     

A second mutant allele (V199I) at the PRKAG3 (RN) locus-II. Effect on colour characteristics of pork loin

Three alleles at the PRKAG3 (RN) locus that influence the glycogen content of pork were found to be segregating in Hampshire×Landrace crossbred pigs, RN(-), rn(+) as well as second mutant allele V 199I (here denoted rn*). The effect of these three alleles on ultimate pH, pigment content, internal reflectance (FOP), surface colour measured by tristimulus colorimetry (L*, a*, b*) and fractions of deoxymyoglobin (Mb), oxymyoglobin (MbO(2)) and metmyoglobin (MetMb) of pork loin was studied. Moreover, the effect of sex, entire male versus female pigs, on these traits was also analysed. The three PRKAG3 alleles affected ultimate pH, internal reflectance, colour and distribution of myoglobin derivatives of pork loin, while the pigment content was not influenced. Ultimate pH values of loins from the three genotypes were found to be in the order RN(-)/- genotypes rn(+)/rn(+) genotype=rn(+)/rn* genotype=rn*/rn* genotype. The RN(-) allele was dominant resulting in higher redness (a* value) and yellowness (b* value), while the rn* allele tended to result in lower redness and yellowness compared with the rn* allele. The RN(-) allele was dominant over the rn* allele in lightness (L* value) giving a lighter colour. Surface colour differences were mainly explained by differences in the distribution of the myoglobin derivatives. Finally, surface lightness was higher and pigment content, redness and fraction of MbO(2) lower in loin from entire males compared with females.     

Effect of the RN gene on technological and sensory meat quality in crossbred pigs with Hampshire as terminal sire

The effect of the dominant RN gene (Rendement Napole) was studied in Hampshire crosses (Hampshire sires × Swedish Landrace-Swedish Yorkshire dams). The present material comprised 107 entire male and 52 female pigs slaughtered at 106 kg live weight. Carriers and non-carriers of the RN gene were distinguished on the basis of the glycolytic potential (GP) in post-mortem longissimus muscle, or with the Napole yield (yield after curing and cooking). Compared with the glycolytic potential classification, Napole classification gave 16% misclassified samples. In comparison with non-carriers of the RN gene, gene carriers showed the following significant differences in m. longissimus dorsi meat quality traits: lower pH, higher surface and internal reflectance values, lower protein extractability, lower water-holding capacity, lower Napole yield and greater cooking loss. The high correlation (r = -0.73; p < 0.001) which was found between GP and Napole yield in the total material, was absent in muscle from individuals carrying the RN gene. In addition to the detrimental effect on meat quality, the RN gene also had beneficial effects. Thus RN carriers had a lower (p = 0.02) shear force value (Warner-Bratzler) and, at sensory testing, a stronger taste and smell and greater acidity (9-member untrained panel). No difference was found in sensory evaluated tenderness.     

The effects of RN genotype and tumbling on processing yield in cured-smoked pork loins

The objective was to investigate the effects of RN genotype and tumbling treatment on yields throughout the processing of cured-smoked loins. Furthermore, the economic outcome was calculated for the different treatments because the technological yield is important for the meat industry. The study comprised two separate trials, T1 and T2, and included loins from 62 and 32 female pigs crossbreed with Hampshire, respectively. All loins in T1 were tumbled, whereas half of the loins in T2 were tumbled and the remainder was non-tumbled. Glucose and glucose-6-phosphate concentrations in meat juice and drip loss were higher, and ultimate pH and technological yield lower in loins of the RN(-) carriers than those of non-carriers. Water loss during processing was largest at heating, when yield between RN genotypes differed the most for T2. Yield between genotypes differed the most at curing for T1. When tumbling was included in the processing the technological yield increased, but the RN allele was still negatively affected. Salt content in cured-smoked loins was higher in non-carriers than RN(-) carriers in T1, whereas salt content in non-tumbled non-carriers was significantly lower than in the other cured-smoked loins in T2. Tumbled cured-smoked loins contained more water than non-tumbled loins. There were moderate to high correlations between ultimate pH and processing yields except for curing yield. Water content in the cured-smoked loins was positively related to technological yield. The differences between the two trials suggest that the process design greatly influences the final product.     

Differences in meat quality between organically and conventionally produced pigs

This study compared organic pig meat production with conventional production with regard to carcass- and meat quality traits. 80 crossbred female and castrated male pigs were used [(Swedish Landrace × Swedish Yorkshire) × Hampshire] of which 40 were raised under organic conditions and the other 40 were raised in a conventional production system. The organic pigs were raised outdoors in one large group following the regulations for organic standards. The conventionally raised animals were kept indoors in groups of eight and were given a conventional feed mixture. It was found that meat of organically raised non-carriers of the RN(-) allele was of poorer quality (higher drip loss and increased shear force values) compared with meat from the other animals. The RN genotype had a relatively small effect on carcass and technological traits in this study. The sex of the animals affected carcass traits.     

Relationship between RN(-) genotype and drip loss in meat from Danish pigs

The presence of the RN(-)-gene determined in 72 halothane negative Danish pigs, either by a direct genotyping or the glycolytic potential of the meat, in relation to drip loss, was investigated. The drip loss in the M. longissimus dorsi from RN-carriers (n=26), as determined by genotyping was 9.9% compared to 8.6% in non-carriers (n=46) (P=0.07). When a glycolytic potential of >230 μmol lactate/g meat was used to differentiate between carriers and non carriers of the RN(-)-gene, the drip loss in carriers was 10.6% (n=17) compared to 8.7% in non-carriers (n=55) (P<0.01). These results suggest that the presence of the RN(-)-gene in Danish slaughter pigs only partially explains the large variation in drip loss observed in Danish pork.     

(31)P NMR study of post mortem changes in pig muscle

The rate and the extent of post mortem pH changes in pig muscle largely determine pork quality. Fast pH fall combined with low ultimate pH leads to pale soft exudative (PSE) meat; high ultimate pH leads to dark firm dry (DFD) meat. Post mortem metabolism was studied in pig muscle using(31)P NMR. Fifteen pigs, i.e. 7 Large White pigs and 8 Pietrain pigs, were used. Five pigs of each breed were slaughtered, taking care to minimize preslaughter stress. The other pigs (3 Large Whites and 2 Pietrains) were injected with 0·1 mg adrenaline per kg liveweight before slaughter, in order to increase meat ultimate pH. All the animals were killed by electronarcosis and exsanguination. Three of the adrenaline-treated pigs (1 Large White and 2 Pietrains) gave meat with ultimate pH above 6 (DFD meat). The pigs with normal muscle ultimate pH, i.e. 6 Large Whites and 6 Pietrains, had very variable rates of post mortem muscle metabolism (pH at 30 min after slaughter: 6·17-6·85 in Large Whites; 6·04-6·23 in Pietrains). The relationships between pH and ATP changes were similar in all pigs showing normal muscle ultimate pH, whereas ATP disappeared at a high pH value (on average pH 6·4) in pigs with high ultimate pH. The course of post mortem biochemical changes in a given animal could be predicted rather well by examination of a single(31)P NMR spectrum obtained around 30 min after death. At this time, muscle with a low rate of metabolism simultaneously showed medium to high pH, high ATP content (4-6·8 μmol/g) and rather low Pi content (6-14 μmol/g); muscle with a fast rate of metabolism (PSE-prone muscle) had low pH, low to medium ATP content (1·1-4 μmol/g) and generally high phosphomonoester (PME) content (9-23 μmol/g); muscle with high ultimate pH (DFD-prone muscle) had high pH, low PME content (4-8 μmol/g) and high Pi content (22-27 μmol/g).     

Free range rearing of pigs with access to pasture grazing - effect on fatty acid composition and lipid oxidation products

The influence of free-range rearing, RN genotype and sex on different pig meat quality traits, including intramuscular fatty acid composition and levels of lipid oxidation products, were studied. A total of 60 Hampshire crossbred pigs were reared outdoors for two months with access to green feed, while 60 others were kept indoors, in a 120-m(2)-large pen, throughout the rearing period. From these 120 animals a subsample of 44 animals was chosen for meat quality analysis. Of the three factors studied, the RN genotype had the largest influence on basic technological meat quality traits, whereas the rearing conditions and sex had limited effects. However, outdoor rearing resulted in higher levels of polyunsaturated fatty acids in the intramuscular fat (P=0.026) and in an increased level of vitamin E (P=0.030) compared with the pigs that had been reared indoors. The sex and RN genotype of the animals also had an effect on the fatty acid profile: females had higher levels of unsaturated fatty acids (P=0.003) as well as lower levels of saturated fatty acids (P=0.011) than castrated males. Carriers of the RN(-) allele expressed a higher sum of omega-3 fatty acids (P=0.047) and C22:5 (P=0.012) than did the non-carriers. In a storage study where meat from free-range and indoor reared pigs was stored for 3 months at-20°C, it was shown that the lipid oxidation product malondialdehyde was formed at increased levels in animals that had a higher lean meat percentage than others, i.e. females that were carriers of the RN(-) gene and that were reared outdoors.     

Rapid prediction of RN phenotype in pigs by means of meat juice

The dominant RN(-) allele occuring in the Hampshire pig breed is associated with a high glycogen content in glycolytic muscles. To determine the RN phenotype in meat, certain alternative rapid methods were studied. Instead of using whole muscle, meat juice released from post-mortem longissimus dorsi muscle was used in the analyses. Carriers of the RN(-) allele were distinguished from non-carriers on the basis of the concentration of glucose + glucose-6-phosphate (spectrophotometrically determined), glucose only (determined with a rapid assay for blood glucose in diabetic patients) or the osmolality of meat juice. These results were compared with a classification based on the glycolytic potential or the residual glycogen (sum of [glycogen], [glucose] and [glucose-6-phosphate]) in muscle. Higher levels of glucose, of the sum of glucose and glucose-6-phosphate, and of osmolality were found in meat juice from animals of the RN phenotype. The sum of glucose and glucose-6-phosphate in meat juice seems to be a reliable marker for the determination of the RN phenotype in meat. Glucose or the osmolality of meat juice can also be used, but more as a preliminary method.     

The effect of RN gene on yields and quality of extended cooked cured hams

The effect of RN(-) allele on minimally processed hams as manufactured in France is now well established. In the present study, meat from 35 rn(+) and 51 RN(-) pigs on the basis of their glycolytic potential (GP) was used to assess the effect of the RN(-) allele on a model system and on yields and quality of cooked hams cured with a 40% brine addition containing the most common meat processing ingredients. Quality parameters were also measured on the fresh loins and a glucose assay was carried out on meat juice from both hams and longissimus dorsi (LD) muscles. With respect to GP, glucose content of LD juice gave the best prediction of RN status with 10% misclassified samples in comparison with 20% as determined from ham juice. Lower pH and higher drip loss and L* values were measured on the LD from RN(-) pigs (p?0.001). Technological yields obtained on the model system and on extended cooked cured hams were lower in meat from RN(-) pigs (p?0.001). However, pH value was more influential on the yield of the model system while protein content and particularly the amount of extractable sarcoplasmic proteins were more determinative on cured hams probably due to the effect of tumbling. All other quality traits were lower in hams from RN(-) pigs (p?0.001). Meat from RN(-) pigs can be used for the manufacture of extended cured products, but under similar processing technologies, quality and yield will remain inferior to what would provide pork of normal quality.     

Pork of low technological quality with a normal rate of muscle pH fall in the immediate post-mortem period: The case of the Hampshire breed

The aim of the experiment was to determine the technological properties of meat from Hampshire pigs, as compared to good quality meat from Large White pigs and to exudative meat from halothane-positive (HP) Pietrain pigs. All Hampshire and Large White pigs were halothanenegative (HN). In 129 females and castrated males (47 Large White, 20 HN Pietrain, 27 HP Pietrain, 35 Hampshire), several quality characteristics were measured on raw meat and one ham was processed into cooked 'Paris ham'. Although the pH was normal I h post mortem in Hampshire pigs (which, in this respect, did not differ from Large White pigs) pork from Hampshire pigs, especially females, showed a very low ultimate pH and the highest cooking loss in processing. However, meat was much less exudative when fresh and generally darker (reflectance measured at 630 nm or subjective colour score) in Hampshire than in HP Pietrain pigs. A low ultimate pH occurred in muscle from Hampshire pigs owing to a very high 'glycolytic potential' (essentially glycogen content). It is proposed to use the term 'Hampshire type' to denote meat whose qualitative inadequacies basically result from an abnormally lowered ultimate pH, and to keep the term 'PSE' to refer to meat whose exudative state comes from an abnormally rapid pH fall in the immediate postmortem period.     

Sensory and meat quality traits of pork in relation to post-slaughter treatment and RN genotype

The effects on eating quality and meat quality of two different forms of post-slaughter treatment, performed in an abattoir, were studied in carriers and non-carriers of the RN(-) allele. Carcasses were subjected to rapid and slow chilling, and pelvic and Achilles suspension in a factorial experimental design. A temperature of 10?°C was achieved in the centre of M. longissimus dorsi (LD) within 3.5 h in rapidly chilled carcasses and within 8 h in slowly chilled carcasses. In deep M. semimembranosus (SM) a temperature of 10?°C was achieved within 11.5 h in rapidly chilled carcasses and within 14 h in slowly chilled carcasses. LD from slowly chilled RN(-) carriers suspended by the pelvis exhibited the greatest tenderness, while LD from rapidly chilled non-carriers suspended from the Achilles tendon exhibited the lowest tenderness. Pelvic suspension or slow chilling of non-carriers produced the same improvement in tenderness, and when combined the tenderness increased further. However, the tenderness of the RN(-) carriers was already high, and no significant improvement was seen following any of the studied post-slaughter treatments. Pelvic suspension prevented shortening of muscle fibres, as seen by longer sarcomeres in LD from pelvic-suspended sides. However, longer sarcomeres were associated with greater tenderness only in LD from non-carriers of the RN(-) allele. The presence of the RN(-) allele and a slow chilling regime increased the rate of pH decline in LD. Achilles suspension also increased the rate of pH fall in SM, in addition to the RN(-) allele and slow chilling. The overall tenderness of LD was mainly related to the course of pH decline during rigor; lower pH values between 3 and 7 h post-mortem contributing to greater tenderness. The myofibrillar length was predominantly related to RN genotype and was shorter in RN(-) carriers than in non-carriers. The RN(-) allele and slow chilling contributed to higher evaporation losses and RN(-) carriers exhibited increased frequency of PSE meat in the ham muscles. The use of pelvic suspension appears advantageous over slower chilling, since it improved tenderness without any negative influence on drip loss, evaporation or cooking loss.     

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).     

Possible mechanism for the effect of the RN(-) allele on pork tenderness

The effect of the dominant RN⁻ allele on rigor development, ageing and tenderness was studied in M. longissimus dorsi (LD) from 11 heterozygous carriers and five non-carriers of the RN⁻ allele. Rigor development was followed by measurements of muscle shortening, isometric tension, pH and FOP. During ageing the myofibrillar length and Warner–Bratzler shear force were measured in the meat. Sensory analysis was performed at 4 days post-mortem using a trained expert panel. It was found that the decrease in pH was faster for RN⁻ carriers than non-carriers during the first 5 h post-mortem, after which the pH-time slope was similar for the two groups. This resulted in a significantly lower mean ultimate pH in LD from RN⁻ carriers than non-carriers. During rigor development the isometric tension was lower in RN⁻ carriers than in non-carriers, while contraction (shortening and sarcomere length) did not differ significantly between the two genotypes. The myofibrillar length, which is an indirect measure of the proteolytic activity that has occurred in the meat, was shorter for the RN⁻ carriers than for the non-carriers. The difference in myofibrillar lengths between the genotypes was significant at 1 and 4 days post-mortem but not at 7 days post-mortem, which indicates that the RN⁻ carriers have a higher proteolytic activity earlier post-mortem. The results from the Warner–Bratzler shear force measurements showed that the meat from the RN⁻ carriers was significantly more tender, 1 and 4 days post-mortem, than the meat from the non-carriers. The meat from non-carriers needed 7 days to reach the tenderness attained by that from the RN⁻ carriers 4 days post-mortem. The greater tenderness in LD from RN⁻ carriers than that from non-carriers was also confirmed by a sensory panel at 4 days post-mortem. In conclusion, differences observed in the course of rigor and ageing in muscle from carriers and non-carriers of the RN⁻ allele suggest that proteolytic action, as initiated by a more rapid fall in pH, is the most important factor governing the variation in tenderness of the two genotypes.     

The influence of breed,gender, and PSS (Halothane) genotype on meat quality,cooking loss,and palatability of pork

A total 851 swine of four breeds (Duroc, Hampshire, Landrace, and Yorkshire), three genders (barrows, gilts, and boars) and two PSS (halothane) genotypes (carriers and non-carriers of the halothane gene) were evaluated for meat quality, cooking, and palatability traits. Breed exerted a major influence on meat quality, cooking, and palatability traits. The most palatable meat was produced by Hampshires and the least desirable meat was produced by Yorkshires. Although juiciness was negatively correlated with cooking loss (r=−0.60), meat from Hampshires received the highest ratings for juiciness, despite sustaining the greatest cooking losses. Gender exerted minor influences on meat quality and palatability attributes, and no indication was obtained genders differed sufficiently in palatability to warrant discrimination based upon gender. Therefore, entire males can be utilized to capitalize on reported production advantages without influencing palatability, particularly if adequate means for screening boar taint are available for carcasses from heavier or more mature animals. Halothane genotype exerted substantial influence on meat quality traits and statistically significant but relatively minor influence on palatability traits. Carriers of the halothane gene produced meat which was of clearly inferior quality to the meat produced by non-carriers. Carriers of the halothane gene consistently produced a higher proportion of unacceptable chops than non-carriers, although differences were not statistically significant.