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

Meat Science 65 (2003) 651–660 www.elsevier.com/locate/meatsci

Sensory quality and the incidence of PSE of pork in relation to crossbreed and RN phenotype A˚sa Josella,*, Gertrud von Sethb, Eva Tornberga,* a

Department of Food Engineering, Lund University, PO Box 124, SE-221 00 Lund, Sweden Tetra Pak Research and Development AB, Ruben Rausings gata, SE-221 86 Lund, Sweden

b

Received 22 July 2002; received in revised form 23 September 2002; accepted 23 September 2002

Abstract 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 24 h post-mortem (pH24 h). 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 pH24 h 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. # 2003 Elsevier Science Ltd. All rights reserved. Keywords: Pork; RN gene; Crossbreed; Tenderness; PSE meat

1. Introduction The Hampshire breed was introduced as the terminal sire in Swedish slaughter pigs in the 1970s, mainly to reduce stress susceptibility and associated problems of meat quality such as the meat’s being pale, soft and exudative (PSE). Since then, however the RN gene has been discovered (Fernandez, Tornberg, Naveau, Talmant, & Monin, 1992; Le Roy, Naveau, Elsen, & Sellier, 1990; Naveau, 1986). Recently, it was found that the dominant RN mutation present in the gene involves a * Corresponding authors. Tel.: +46-46-222-4821; fax: +46-46-2224622. E-mail addresses: [email protected] (A˚ Josell), [email protected] (E. Tornberg).

substitution in the PRKAG3 gene (Milan et al., 2000). In Sweden, approximately 65% of all slaughter-pigs in which Hampshire has been the sire, carry the RN allele (Josell, Martinsson, Borggaard, Andersen, & Tornberg, 2000). Since Hampshire crosses constitute the majority of the pigs that go to slaughter in Sweden, a large portion of the pigs slaughtered are carriers of the RN allele. Meat from pigs carrying the RN allele is of major concern for the industrial production of cured and cooked pork products, since the specific characteristics of both the ultimate pH and the protein content being low result in low yields (Eber & Mueller, 1999; Enfa¨lt, Lundstro¨m, Hansson, Johansen & Nystro¨m, 1997; Lundstro¨m, Enfa¨lt, Tornberg & Agerhem, 1998; Monin & Sellier, 1985). The RN mutation is only found in purebred Hampshire and in crosses with it.

0309-1740/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0309-1740(02)00268-1

652

A˚. Josell et al. / Meat Science 65 (2003) 651–660

Consequently, companies producing cured and cooked products often prefer meat from breeds other than Hampshire. On the other hand, the Hampshire breed has been shown to produce more tender meat [M. longissimus dorsi (LD)] than that of Yorkshire or Landrace and juicier than that of Yorkshire (Fjelkner-Modig, 1985). The marked tenderness of meat from the Hampshire breed has been found recently to be associated with the RN gene (Jonsa¨ll, Johansson, & Lundstro¨m, 2000, 2001; Josell, Martinsson & Tornberg, in press; Lundstro¨m, Andersson, & Hassson, 1996; Miller, Ellis, Bidner, McKeith, & Wilson, 2000; van Laack, Stevens, & Stadler, 2001). Traditionally, Swedish consumers eat a higher proportion of fresh meat than consumers in most other European countries, in which cooked and cured products tend to be favoured. The Swedish meat industry has thus continued, in contrast to France, for example, to use both Hampshire and carriers of the RN allele for slaughter pig production. There is a trend in Sweden, however, towards increasing demand for cured and cooked meat products. In order to meet this demand, the Swedish slaughter industry needs to increase the production of meat of high water-holding capacity that is high in pH. At the same time, the acceptability of it for consumers depends upon the eating quality of the fresh cut and of its retaining a high level of quality. The aim of this study was to investigate different crossbreeds that are available in Sweden with regard to eating and meat quality parameters. Fjelkner-Modig (1985) found that purebred Hampshire contributes more strongly to the level of tenderness being high than either Yorkshire or Landrace do. The eating quality of meat from a Hampshire crossbreed as compared with meat from a Duroc crossbreed from the Swedish pig population remains to be investigated, however. Meat from Duroc in the Danish pig population has been shown to be good in eating quality (Barton-Gade, 1988). For several decades, breeding strategies aimed at producing lean, rapidly growing and halothane-free pigs have been highly successful, resulting in pigs that differ not only in their stress tolerance and their production attributes but also in meat quality as compared with earlier. Because of changes in the genetic material within the various breeds, there is a continuous need of new investigations being conducted, despite a substantial amount of research on the influence of breed on meat quality having been carried out over the years. The Hampshire breed illustrates changes in genetic material that can occur, its RN carriers having been indirectly favoured by the fact that these animals are leaner and grow faster than non-carriers (Enfa¨lt et al., 1997). Since Fjelkner-Modig’s (1985) investigation of the influence of breeds on the eating quality of meat,

breeding has continued, resulting in considerable changes in the genetic material. Through halothane carriers having been largely eliminated in Yorkshire and in Swedish Landrace, pigs of both breeds, as well as Hampshires, are no longer strongly stress-susceptible. Instead, there are indications that, despite the Hampshire breed’s being much less stress-susceptible, PSE can develop in its meat (Barton-Gade, 1987; Purchas, Smith, & Pearson, 1990). Since carriers of the RN allele display a more rapid fall in pH during rigor than non-carriers do, as shown by Josell et al. (in press), it can be assumed that unless the meat is chilled sufficiently RN carriers are more likely to develop PSE than non-carriers are. In the present study, the frequency of PSE in the different crossbreeds and RN phenotypes was also investigated.

2. Material and methods 2.1. Experimental material The animals used in the study were crosses between Swedish Landrace  Yorkshire (LY) sows and Hampshire (H), Duroc (D), Yorkshire (Y) or Hampshire  Yorkshire (HY) sires. Some 250–325 pigs of each crossbreed were reared by the same producer. The pigs were off-feed 4 hours before transportation according to Swedish recommendations and the transportation time was approximately 30 min. They were allowed to rest for 2 h in the lairage prior to slaughter. All the pigs were slaughtered at the same abattoir, stunned individually with CO2 and chilled conventionally in a chilling tunnel ( 16  C for 70 min). Meat-quality traits were registered on 135–200 pigs of each crossbreed. Ten animals from each crossbreed except for the LYH crossbreed, for which there were 10 RN carriers and 10 non-carriers, a total of 50 pigs, altogether, were selected for sensory and chemical-composition analyses. To ensure normal meat, the 50 pigs selected were ones found to have a pH value above 6.0 as measured 45 min post-mortem and below 6.0 as measured 24 h post-mortem in M. longissimus dorsi (LD) at the last rib. The pigs selected were also ones in which the FOP values as measured in LD 24 h post-mortem (FOP24) were between 20 and 55. The LD muscles of the 50 pigs selected were excised 2 days after slaughter and were cut into pieces for the different analyses. 2.2. Measurements 2.2.1. Meat quality traits On 135–200 pigs of each crossbreed, the carcass weight and percentage of lean meat (Hennessy Grading probe, Hennessy & Chong Ltd., Auckland, New Zealand) were registered on the slaughter-line 45 min post-

A˚. Josell et al. / Meat Science 65 (2003) 651–660

mortem. The pH was measured 45 min (pH45) and 24 h (pH24h) post-mortem in the LD muscle at the last rib using a Knick Portamess 911 pH-meter and a Xerolyte glass-combination electrode. Internal light scattering was measured 24 h (FOP24) post-mortem in the LD muscle at the last rib, using a Fibre Optic Probe instrument (900 nm, TBL Fibre Optics Group Ltd, Leeds, UK). The occurrence of PSE spots in the LD muscle between the third and forth thoracic vertebra and in the ham muscles around the femur were scored visually according to the scale: 0: no PSE meat; 1: small visible PSE-spots; 2: PSE-spots of 3–7 cm in diameter; 3: PSEmeat of more than 7 cm in diameter in the ham or loin. For the 50 selected pigs, pH and FOP were also measured 48 h post-mortem (pH48 h and FOP48 h) in M. longissimus dorsi (LD), M. biceps femoris (BF), M. semimembranosus (SM), M. quadriceps femoris (QF), M. semitendinosus (ST) and M. gluteus medius (GM). The drip loss was determined according to Honikel (1998) in the LD of the 50 selected pigs. Two 2-cm thick slices were cut from the LD, at the last rib and towards the ham, 48 h post-mortem. The drip loss, expressed as percentage of the initial weight, was determined after storage of the meat for 2 days at +4  C.

653

between the two modes in the bimodal distribution as a threshold value (Fernandez et al., 1992). Since the pig material involved a three-way crossbreed, the RN allele could only be transferred from the Hampshire, the pigs studied thus being either heterozygous carriers or noncarriers of the RN allele. For the 50 selected pigs the glycogen, the glucose and the glucose-6-phophate content in the LD muscle were analysed. 2.2.3. Sensory analysis Sensory evaluation was carried out on LD stored post-mortem for 4 days at 4  C. All the meat was frozen prior to the sensory analysis so as to allow the evaluation to be performed after all the meat had been collected. Prior to sensory evaluation, the samples were thawed overnight at 4  C. The LD was cut into 2-cmthick slices and was fried on a griddle at 165  C to an internal temperature of 68  C. After frying, the meat was served directly to a trained panel consisting of 12 people. The samples of LD were judged with respect to tenderness, chewing resistance, chewing time, juiciness, meat flavour and acidity. Each sensory attribute was assessed on a nine-point scale, 1 corresponding to very tough, very low resistance, very short chewing time, very dry, weak flavour and no acidity, and 9 to very tender, very high resistance, very long chewing time, very juicy, strong flavour and strong acidity.

2.2.2. Chemical analysis For the 50 selected pigs the chemical composition was determined in a 4-cm section of the LD muscle removed at the last rib and cut towards the shoulder. The contents of intramuscular fat (IMF) (NMKL, 1989), protein (AOAC, 1974) and water (NMKL, 1991) were analysed. The glycogen content of SM was determined in 166 of the LYH pigs in order to classify them as carriers or noncarriers of the RN allele. One gram of meat was homogenised in 5 ml cold perchloric acid. The sum of glycogen and glucose was determined in the homogenate by use of enzymatic methods, following the hydrolysis of the glycogen by amyloglucosidase (Dalrymple & Hamm, 1973). The animals were classified in terms of the presence of the RN allele, using the value of glycogen and glucose

2.2.4. Statistical analysis The results were evaluated statistically using one-way analysis of variance, independent t-tests and Tukey’s ttest in SYSTAT (Wilkinson, Leland, version 5.03).

3. Results and discussion 3.1. Meat quality traits The meat quality traits of the four different crossbreeds studied are shown in Table 1. Crossbreed had a

Table 1 Mean values and standard deviations for meat quality traits of M. longissimus dorsi (LD) and M. semimembranosus (SM) from different crossbreeds Trait

Slaughter weight (kg) Lean meat (%) pH45 LD pH24 h LD pH24 h SM FOP24 h LD FOP24 h SM a

LYH (n=207)

LYY (n=171)

Mean

S.D.

Mean

83.3a 60.2a

6.5 2.0

86.0b 59.9a,b

6.46d 5.40a 5.47a 35.3a 42.8a

0.22 0.12 0.19 6.2 10.1

6.45d,e 5.47b 5.61b 37.5a,b 36.7b,c

P-valuea

LYD (n=195)

LYHY (n=135)

S.D.

Mean

S.D.

Mean

S.D.

5.2 2.1

83.1a 59.3b

5.3 2.0

82.6a 60.2a

5.6 1.8

40.001 40.001

0.23 0.13 0.24

40.001 40.001 40.001

7.4 7.8

40.001 40.001

0.23 0.12 0.20 8.8 9.0

6.38e 5.44b 5.59b 39.4b 39.0c

0.23 0.10 0.16 7.8 10.5

6.47d 5.48b 5.61b 35.4a 33.8b

According to one-way analysis of variance. Means of differing letter within a row differ significantly: a, b, c: P40.001; d, e: P40.010.

654

A˚. Josell et al. / Meat Science 65 (2003) 651–660

significant influence on all measured traits. The pH, measured 45 min post-mortem (pH45), was found to be lower in LD from LYD (pH=6.38) than in that from the other crosses (pH 6.45–6.47). The difference in comparing LYD with LYH and LYHY was significant (P=0.010). The frequency of animals with a pH45 below 6.0 was highest for LYD (6%). The pH, measured 24 h post-mortem, was significantly lower in both LD and SM from LYH than in those from the other crossbreeds. This result was expected since 70% of the LYH pigs were found to be carriers of the RN gene. The FOP24 value was found to be significantly higher in the SM from LYH than in that from the other crossbreeds, whereas the crossbreeds did not differ in the FOP-values obtained in LD. The slaughter weight was significantly higher in LYY than in the other crossbreeds (P=0.001). The percentage of lean meat was lowest in LYD, intermediate in LYY and highest in LYH and LYHY; LYD having a significantly lower percentage of lean meat than LYH and LYHY (P40.001). Carriers and non-carriers of the RN allele of LYH were classified on the basis of the post-mortem distribution of the glycogen content in the SM muscle, using the valley between the bimodal peaks as the threshold (Fernandez et al., 1992; Lundstro¨m et al., 1996). Altogether, 70% of the animals were considered to be carriers, having a glycogen level above 20 mmol/g, and 28% to be non-carriers, having a glycogen level below 16 mmol/g. An additional 2% remained unclassified, having a glycogen content between 16 and 20 mmol/g. The frequencies of RN carriers and non-carriers were in the same range as obtained in previous investigations, reflecting the frequency of RN carriers in the Swedish slaughter-pig population (Josell et al., 2000). In Fig. 1, the distribution of pH24 h at different levels when account is taken of the RN phenotype is shown. As can be seen, the low pH in the LYH-crossbreed (Table 1) originated from the RN carriers. The pH was 5.5 or less in 100% of the LDs and in 98% of the SMs

from the RN carriers. The non-carriers of the RN allele from LYH had nearly the same pH distribution as the other three crossbreeds. In comparing the pH-values in LD with those in SM, the pH of the two muscles was found to not differ in RN carriers, whereas the pH was higher in SM than in LD for the non-carriers of the RN allele as well as for the other crossbreeds. Ten pigs of each crossbreed except for the LYH crossbreed, for which there were 10 RN carriers and 10 non-carriers, were selected for further analyses. Only normal meat was used, where PSE or dark, firm and dry (DFD) meat according to FOP, pH45, pH24 h or visual appearance was excluded. The slaughter weight and the percentage of lean meat in all the groups were similar (on average 83 kg and 60%, respectively), assuring the same chilling rate for all the crossbreeds. The meat quality traits for the pigs selected are shown in Table 2. The groups did not differ in pH45 or in FOP values, due to the conditions being specified. The LD from RN carriers in LYH had a significantly lower pH24 h than non-carriers in LYH or than LYD did. LYY and LYHY having an intermediate position. For the pH as measured 48 h post-mortem (pH48 h) in LD the same basic differences between the crossbreeds were found as for pH24 h and the pH values were almost the same. Thus, the ultimate pH was more or less reached 24 h post-mortem. For the various muscles in the ham (SM, BF, QF, ST and GM), the pH48 h was found to be lower in RN carriers of LYH than in the other crossbreeds or in the non-carriers of LYH (Table 2). The pH48 h of SM was significantly lower in the RN carriers than in the noncarriers from LYH (P=0.002), and than that in LYY (P=0.016), LYD (P=0.001) and LYHY (P=0.035). In addition, for BF and QF the pH was significantly lower in LYH RN carriers than in LYH non-carriers, LYY and LYD (BF: P=0.002, 0.038, 0.003; QF: P=0.010, 0.001, 0.002). Furthermore, for GM and ST the pH was significantly lower in LYH RN carriers than in LYH

Fig. 1. Variation in pH24 h in M. longissimus dorsi (LD) and M. semimembranosus (SM) of different crossbreeds and RN phenotypes (RN : RN carriers and rn+: non-carriers). No. of samples in each group: LYH RN : 117; LYH rn+: 46; LYY: 171; LYD: 195; LYHY: 135.

A˚. Josell et al. / Meat Science 65 (2003) 651–660

655

Table 2 Mean values and standard deviation for meat quality traits of M. longissimus dorsi (LD), M. semimembranosus (SM), M. biceps femoris (BF), M. quadriceps femoris (QF), M. gluteus medius (GM) and M. semitendinosus (ST) from different crossbreeds and RN phenotypes (N=10 per crossbreed and phenotype) LYH

pH45 LD FOP24 h LD pH 24 h LD pH 48 h LD pH48 h SM pH 48 h BF pH 48 h QF pH48 h GM pH 48 h ST Glucose, G-6-P, glycogen (mmol/g) Water (%) IMF(%) Protein (%) Drip (%)

RN carriers

Non-carriers

6.47 37.7 5.36a 5.34a 5.39a 5.40a 5.46a 5.37a 5.43a 80.9a,c 76.0a 1.53a, b 21.2a,c 5.38

6.43 37.8 5.53b 5.49b 5.52b 5.55b 5.73b 5.46b 5.77b 15.2b 74.9b 1.43a, b 23.1b 4.11

LYY

LYD

LYHY

SE

P-value

6.46 39.5 5.45a,b 5.42a,b 5.49b 5.51b 5.79b 5.43b 5.58a,b 17.8b 75.1b 1.14a 23.2b 5.11

6.43 40.2 5.46b 5.44b 5.53 b 5.55 b 5.78 b 5.46 b 5.63 b 17.6b 75.0b 1.70b 22.9b 4.77

6.52 38.5 5.42a,b 5.40a,b 5.48 b 5.48 a, b 5.63 a, b 5.47 b 5.64 b 37.5d 75.9a 1.23a, b 22.1d 4.49

0.05 1.5 0.02 0.02 0.02 0.03 0.06 0.02 0.05 4.4 0.2 0.13 0.2 0.34

0.738 0.703 40.001 40.001 40.001 40.001 40.001 0.008 40.001 40.001 40.001 0.010 40.001 0.080

Means of differing letter within a row differ significantly: a, b: P40.001 and c, d: P40.010.

non-carriers, LYD and LYHY (GM: P=0.032, 0.025, 0.011; ST: P=0.000, 0.040, 0.032). It can be concluded that also for muscles such as BF with a more red and oxidative metabolism the pH was lower for RN carriers than for the other groups. This agrees with the results for BF and LD reported by Lundstro¨m et al. (1996) in comparing RN carriers and non-carriers in Hampshire crossbreeds. As can be seen for the material as a whole, as shown in Fig. 1, SM and LD differed in the variation in pH found between the LYH RN carriers and the other crossbreeds. In the selected material (N=50), the variation in mean pH values in different muscles was less for LYH RN carriers (between 5.37 and 5.46) than for the other groups (between 5.47 and 5.64 for LYHY and between approximately 5.45 and 5.78 for the other crossbreeds). Monin, Mejenes-Quijano, Talmant, and Sellier (1987), in comparing Penshire with Pietrain, Large White and Belgian Landrace, have shown the breed differences in the ultimate pH to be smaller for the fast white LD and SM muscles than for the more red muscles (Gluteus superficialis, adductor), despite the glycolytic potential varying most in the fast white muscles. As expected, the sum of glycogen, glucose and glucose-6-phosphate in LD was significantly higher in RN carriers than in the other groups. It can also be seen in Table 2, that the sum of glycogen, glucose and glucose6-phosphate in LD from LYHY was intermediate to that of the RN carriers and non-carriers in LYH. Four of the LDs in LYHY could be classified as RN carriers. In the statistical evaluation no consideration was taken, however, of the RN phenotype in LYHY. The protein content was significantly lower in the LD from the LYH RN carriers than in that from LYH non-carriers, LYY, LYD and LYHY (P40.01). Con-

sequently, the water content was significantly higher in the LD from the LYH RN carriers than in that from LYH non-carriers, LYY and LYD (P40.001). RN carriers have been shown to have a low protein and a high water content (Lundstro¨m et al., 1998). The highest content of IMF was found in the LD from LYD and the lowest in that from LYY, whereas in LYH (both in carriers and non-carriers of RN ) and LYHY the level of IMF was intermediate to these (Table 2). The higher concentration of intramuscular fat found in the Duroc crossbreed is consistent with previous findings for purebred Duroc pigs (Jeremiah, Gibson, Gibson, Ball, Aker, & Fortin, 1999; Wood et al., 1996; Barton-Gade, 1988). 3.2. PSE The PSE quality defect can arise in different ways, the way investigated most being that of stress inducing a rapid early post-mortem decline in pH and of the relatively high temperature in the muscle which accompanies this causing denaturation mainly of the myosin and sarcoplasmic proteins there (Bendall & WismerPedersen, 1962). Since successful breeding strategies have lowered the frequency of halothane carriers and animal handling has improved, stress-induced PSE meat has been more or less eliminated. Of the crossbreeds investigated here, LYD showed the highest frequency (6%) of pH45 being below 6.0, which is indicative of stress-induced PSE. In terms of FOP as measured 24 h post-mortem, LYD also had the highest PSE-frequency and 1 and 6% in LD and SM, respectively, having a FOP above 55. The FOP instrument measures the reflectance at 900 nm, where the absorbance of myoglobin is minimal, and has been shown by

A˚. Josell et al. / Meat Science 65 (2003) 651–660

656

Larsson and Tornberg (1988) and Oliver, Gispert, Tibau and Diestre (1991) to be able to identify PSE meat. Larsson and Tornberg (1988) concluded that FOP values above 55 in LD muscle 24 h post-mortem are indicative of PSE meat. In Table 3 it can be seen that in terms of FOP the SM from RN carriers had a higher incidence of PSE meat than the other crossbreeds or the RN phenotype. No PSE could be detected, on the other hand, in the LD of the RN carriers. However, FOP is difficult to measure since the occurrence of PSE can vary within the muscle. Accordingly, ocular assessment was also performed, the results being summarised in Table 3. This showed the RN carriers to have a relatively high proportion of PSE meat (scored 3 in the visual assessment) in the ham muscles around the femur (23%), there being only a small proportion of PSE meat in the LD. This is also consistent with the results of the FOP measurements (Table 3). RN carriers have been found to display a more rapid fall in pH than non-carriers during the first 5 h postmortem (Josell et al., in preparation). This difference in pH decline does not occur immediately post-mortem, however, as can be seen in stress-susceptible pigs. Instead, the difference in pH first becomes noticeable approximately 3 h post-mortem. PSE has been shown to develop, especially in the deep musculature, if the carcass is cooled too slowly, even if the pH falls at a nearly normal rate, since the temperature remains high for a long time (MacDougall, 1982; Offer, 1991). Fernandez, Forslid, and Tornberg (1994) have shown that a high temperature at the onset of rigor contributes more strongly to the development of PSE, when the ultimate pH is low. Since, the pigs used in the study of Fernandez et al. (1994) consisted of Hampshire crossbreeds, it is likely that the carcasses of low ultimate pH were carriers of the RN allele. Under normal chilling conditions, RN carriers with a somewhat faster than normal pH fall, may develop PSE meat in the deep musculature, where the cooling is slow. This makes it appear more likely for PSE meat to develop in slowly chilled ham

than in the superficial loin meat, the present results also supporting this. As discussed in the literature the presence of RN carriers or of high glycolytic potential may contribute to the development of RSE (red, soft and exudative) meat (van Laack & Kauffman, 1999). Such meat, which is acceptable in colour but has excessive drip loss, does not show the extensive denaturation of the myofibrils and the sarcoplasmic proteins as PSE meat does (Warner, Kauffman, & Greaser, 1997). In the present study the drip loss in LD, as measured in the 50 selected pigs, was somewhat higher in the LYH RN carriers than in the other crossbreeds, but the difference was not significant. Small and non-significant differences in drip loss due to the presence or lack of the RN gene were also observed by van Laack and Kauffman (1999) and Bertram, Petersen, and Andersen (2000). No relationship between high glycolytic capacity and RSE occurrence has thus been confirmed, so far. Van Laack and Kauffman (1999) found drip loss to be related both to glycolytic potential (r=0.61 and P < 0.01) and to pH (r= 0.73, P < 0.01), indicating the risk for RSE and PSE to increase when the RN gene is present. In the present study the drip loss was relatively high (varying between 3 and 7%), considering the fact that PSE meat had been excluded. This could indicate that some of the samples in the present investigation were of RSE quality. The lower pH in the RN carriers probably contributed to the higher drip loss obtained for them, a significant relationship between pH and drip loss being found (r= 0.523, P=0.000). As can be seen in Fig. 2, however, the relationship was, not entirely clear, there being

Table 3 PSE-frequency in the different crossbreeds and RN phenotypes. No of samples as in Fig. 1 LYH

pH45 46.00 (%) FOP24 h > 55 LD (%) SM (%) Visually LD (%) Around femur (%)

RN carriers

Noncarriers

LYY

LYD

LYHY

<1

<1

<1

6

3

0 10

0 0

<1 1

1 6

0 0

0 23

0 0

1 1

2 4

1 4

Fig. 2. Drip loss as a function of ultimate pH (r= 0.523 and P=0.000).

A˚. Josell et al. / Meat Science 65 (2003) 651–660

samples from the RN carriers with a pH of 5.3 which exhibited drip losses of less than 5%. Tornberg, Andersson, and von Seth (1993) also found there to be a significant relationship between pH and drip loss in normal (i.e. neither PSE nor DFD) meat. The ultimate pH has been shown to be 0.1 pH units lower in RSE meat than in normal meat (Warner et al., 1997). Joo, Kauffman, Kim, and Park (1999) showed that in RSE meat the low ultimate pH is responsible for the low WHC, but that in PSE meat both denaturation of the myofibrillar proteins and the low ultimate pH contribute to the low WHC. In the same study, WHC was found to be more strongly correlated with sarcoplasmic protein solubility than with myofibrillar protein solubility. RSE meat was also found to differ from DFD meat in sarcoplasmic protein solubility, but not in myofibrillar protein solubility. These results agree with the findings of Lopez-Bote, Warriss, and Brown (1989), who showed the amount of denatured sarcoplasmic proteins in both PSE and DFD meat to differ significantly from that found in normal meat and the amount of denatured sarcoplasmic proteins to be correlated with drip loss. Their findings suggest a gradual denaturation of the sarcoplasmic proteins from severe PSE to DFD. RSE would then result in a mild form of PSE. The specific conditions (in terms of pH, time postmortem and temperature) that result in denaturation of the sarcoplasmic proteins and to what extent they are denatured remains to be investigated. It seems likely, however, that pigs with a decline in pH more rapid than normal but not as rapid as in stress-susceptible pigs could develop PSE that is not as severe as stress-induced PSE, it being similar to what is found in RSE. 3.3. Sensory analysis Table 4 presents results of the sensory analysis. The meat from RN carriers received higher tenderness and lower chewing resistance and time ratings than that of the other phenotypes or crossbreeds. Tenderness was significantly higher and chewing time significantly lower in the LYH RN carriers than in the LYH non-carriers,

657

as well as in LYD and LYHY, whereas the only significant difference in chewing resistance was between RN carriers and non-carriers in the LYH crossbreed. The present findings suggest that the high degree of tenderness reported earlier for the Hampshire breed originates from the specific characteristics of the RN carriers. The results in Table 4 also suggest that if the RN allele were eliminated in pigs for purposes of meat production, the tenderness of the Hampshire breed would be in the same range as that of the other crossbreeds or would be even less. In some investigations, Duroc has been found to produce meat of good eating quality. As early as 1967, when Jensen, Craig, & Robison (1967) found that Hampshire produced meat of low shear force, Duroc was shown to have a shear force close to that of Hampshire. Similar results have been reported more recently (Jeremiah et al., 1999; Warriss, Kestin, Brown & Nute, 1996). Barton-Gade (1988) even reported meat from Hampshire to be lower in tenderness than that from Duroc. In that investigation, however, the pH was not found to be significantly lower in the Hampshire breed than in the Duroc breed, which indicates the proportion of RN carriers in the Hampshire breed that was studied to be low. In the present investigation, in contrast, the eating quality of the crossbreed with Duroc did not receive a good rating. The fact that the LD from LYD had the highest intramuscular fat content without being tender substantiates the previous conclusion that a direct relationship between IMF (varying from 0.5 to 2.9%) and tenderness does not exist (Go¨ransson, von Seth, & Tornberg, 1992). The relationship between IMF and tenderness can be seen in Fig. 3. There are investigations showing breeds to differ in the relationship between IMF and tenderness. Fjelkner-Modig and Tornberg (1986) found no relationship between IMF and tenderness in purebred Hampshire, whereas in Yorkshire an increase in the level of IMF was found to result in greater tenderness. Similarly, van Laack et al. (2001) found there to be a significant relationship between IMF and tenderness (shear force) in crossbreeds from Duroc but no such relationship to be found in

Table 4 Least square means and standard errors (S.E.) for sensory properties in M. longissimus dorsi (LD) from different crossbreeds and RN phenotypes (N=10) LYH

Chewing resistance Chewing time Tenderness Juiciness Meat flavour Acidity

RN carriers

Non-carriers

LYY

LYD

LYHY

SE

P-value

3.92a 4.78a 5.69a 5.59a 4.67 4.16a

5.12b 5.85b 4.36b 5.02b 4.61 3.43b

4.39a,c 5.22a,b 5.13a,b 5.06a,b 4.43 3.94a,b

4.61a,b,c 5.46b 4.79b 4.83b 4.49 3.65a,b

4.88b,c 5.55b 4.61b 5.24a,b 4.77 3.56b

0.17 0.16 0.21 0.13 0.09 0.14

0.000 0.001 0.001 0.003 0.069 0.003

Means within a row with different letters are significantly different: a, b, c: P 40.05.

658

A˚. Josell et al. / Meat Science 65 (2003) 651–660

Jeremiah et al., 1999). Jeremiah et al. (1999) evaluated the palatability traits of a large number of longissimus thoracis muscles from Duroc, Hampshire, Yorkshire and Landrace pigs, finding the Hampshire breed to produce the most palatable meat. Hampshire received the highest ratings for juiciness and tenderness despite having the greatest cooking losses. The variation in meat flavour in the LDs was small and did not differ significantly between the crossbreeds. Acidity was rated as being highest in the meat from RN carriers in LYH, followed by LYY, LYD, LYHY and non-carriers of the RN allele in that order. The high degree of acidity of meat from RN carriers was expected, due to the low ultimate pH in this phenotype, a result consistent with findings reported by Jonsa¨ll et al. (2000) and Josell et al. (in press). Despite part of the LYHY crossbreed consisting of RN carriers, the LDs from this crossbreed received a low rating in the taste of acidity. Fig. 3. Tenderness as a function of intramuscular fat content in M. longissimus dorsi (LD).

crossbreeds from Hampshire or Berkshire. As can be seen in Fig. 3, no influence of IMF on tenderness could be detected in any of the crossbreeds investigated. The crossbreed rated next in tenderness after the LYH RN carriers in the present study was LYY. This result was unexpected, since most previous findings have indicated the eating quality of meat from Yorkshire crosses to be low (Fjelkner-Modig, 1985; Jensen et al., 1967; Purchas et al., 1990). The relatively low rating of tenderness that LD from LYHY received was also unexpected, since four of the LYHY pigs were carriers of the RN allele. In fact, within LYHY the RN carriers were found to have a higher degree of tenderness than the non-carriers. Nevertheless, the RN carriers of LYHY were less tender than the RN carriers of LYH and at the same time there was a tendency for the non-carriers of LYHY to be less tender than non-carriers of LYH, resulting in a lower average tenderness for LYHY. The pH24 h of LD from the RN carriers of LYHY was not as low as expected. This could indicate that the fall in pH had been basically normal in this group. A rapid fall in pH in meat from RN carriers during rigor (approximately 3–5 h pm), which resulted in a low ultimate pH, has been suggested as a possible cause of the high degree of tenderness in meat from RN carriers (Josell et al., in press). Juiciness was found to be greatest in meat from RN carriers of the LYH crossbreed, LYH RN carriers being found to differ significantly from LYH non-carriers and from LYD. The finding that meat from LYH RN carriers, which had the lowest water-holding capacity, was the juiciest confirms results of earlier studies of purebred Hampshire (Fjelkner-Modig, 1985;

4. Conclusions M. longissimus dorsi (LD) and M. semimembranosus (SM) from LYH had the lowest pH of the crossbreeds investigated as measured 24 h post-mortem (pH24 h). The low pH in the LYH crossbreed originated from the large proportion of RN carriers (approximately 70%), whereas the non-carriers of the RN allele in the LYH crossbreed had a pH24 h close to that of LYD, LYY and LYHY. In the selected group of pigs (N=50), the ultimate pH was also found to be lower in the ham muscles M. biceps femoris (BF), M. quadriceps femoris (QF), M. gluteus medius (GM) and M. semitendinosus (ST) from RN carriers of LYH than in those of the other crossbreeds. 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 sensitive to the development of PSE. Tenderness, as rated by the trained sensory panel was found to be significantly higher in LD from carriers than in LD from LYD, LYHY and non-carriers of the RN allele of LYH. The tenderness of LD from LYY was rated as being intermediate. The highest intramuscular fat content was found in the LD from LYD. No relationship between intramuscular fat content and tenderness could be detected.

Acknowledgements The authors wish to thank Pia Ohlsson, Lena Sjo¨berg and Jonas Bja¨rstorp for their skilful technical assistance. This work was undertaken at Swedish Meat R&D (no longer in operation) and was funded by Swedish Meats.

A˚. Josell et al. / Meat Science 65 (2003) 651–660

References AOAC Official Method 928.08 (1974). Nitrogen in meat. Kjeldahl method. Barton-Gade, P. A. (1987). Meat and fat quailty in boars, castrates and gilts. Livestock Production Science, 16, 187–196. Barton-Gade, P.A. 1988. The effect of breed on meat quality characteristics in pigs. In Proceedings of the 34th International Congress of Meat Science and Technology. Brisbane, Australia. Bendall, J. R., & Wismer-Pedersen, J. (1962). Some properties of the fibrillar proteins of normal and watery pork muscle. Journal of Food Science, 27, 144–159. Bertram, H. C., Petersen, J. S., & Andersen, H. J. (2000). Relationship between RN genotype and drip loss in meat from Danish pigs. Meat Science, 56, 49–55. Dalrymple, R. H., & Hamm, R. (1973). A method for the extraction of glycogen and metabolites from a single muscle sample. Journal of Food Technology, 8, 439–444. Eber, M., & Mueller, W.-D. (1999). Studies on the suitability of Hampshire-type meat for processing cooked ham. Fleischwirtschaft International, 1, 19–22. Enfa¨lt, A-C., Lundstro¨m, K., Hansson, I., Johansen, S., & Nystro¨m, P-E. (1997). Comparison of non-carriers and heterozygous carriers of the RN allele for carcass composition, muscle distribution and technological meat quality in Hampshire-sired pigs. Livestock Production Science, 47(3), 221–229. Fernandez, X., Forslid, A., & Tornberg, E. (1994). The effect of high post-mortem temperature on the development of pale, soft and exudative pork: interaction with ultimate pH. Meat Science, 37, 133–147. Fernandez, X., Tornberg, E., Naveau, J., Talmant, A., & Monin, G. (1992). Bimodal distribution of the muscle glycolytic potential in French and Swedish populations of Hampshire crossbred pigs. Journal of the Science of Food and Agriculture, 59, 307–311. Fjelkner-Modig, S., & Tornberg, E. (1986). Intramuscular lipids in M. longissimus dorsi from pork, as related to breed and sensory properties. Journal of Food Quality, 9, 143–160. Fjelkner-Modig, S. (1985). Sensory and biophysical properties of pork. PhD thesis, Lund University, Lund, Sweden. Go¨ransson, A˚., von Seth, G., & Tornberg, E. (1992). The influence of intramuscular fat content on the eating quality of pork. In Proceedings of the 38th International Congress of Meat Science and Technology. Clermont Ferrand, France. Honikel, K. O. (1998). Reference methods for assessment of physical characteristics of meat. Meat Science, 49(4), 447–457. Jensen, P., Craig, H. B., & Robison, O. W. (1967). Phenotypic and genetic associations among carcass traits of swine. Journal of Food Science, 26, 1252–1260. Jeremiah, L. E., Gibson, J. P., Gibson, L. L., Ball, R. O., Aker, C., & Fortin, A. (1999). The influence of breed, gender, and PSS (Halothane) genotype on meat quality, cooking loss, and palatability of pork. Food Research International, 32, 59–71. Jonsa¨ll, A., Johansson, L., & Lundstro¨m, K. (2000). Effects of red clover silage and RN genotype on sensory quality of- prolonged frozen stored pork (M. Longissimus dorsi). Food Quality and Preference, 11, 371–376. Jonsa¨ll, A., Johansson, L., & Lundstro¨m, K. (2001). Sensory quality and cooking loss of ham muscle (M. biceps femoris) from pigs reared indoors and outdoors. Meat Science, 57, 245–250. Joo, S. T., Kauffman, R. G., Kim, B. C., & Park, G. B. (1999). The relationship of sarcoplasmic and myofibrillar protein solubility to colour and water-holding capacity in porcine longissimus muscle. Meat Science, 52, 291–297. Josell, A˚., Martinsson, L., & Tornberg, E. (2002) Possible mechanism for the effect of the RN allele on pork tenderness. Meat Science (in press).

659

Josell, A˚., Martinsson, L., Borggaard, C., Andersen, J. R., & Tornberg, E. (2000). Determination of RN- phenotype in pigs at slaughter-line using visual and near-infrared spectroscopy. Meat Science, 55, 273–278. Larsson, G., & Tornberg, E. (1988) An attempt to relate meat quality of pork (M. longissimus dorsi) to meat structure. In Proceedings of the 34th International Congress of Meat Science and Technology. Brisbane, Australia. Le Roy, P., Naveau, J., Elsen, J. M., & Sellier, P. (1990). Evidence for a new major gene influencing meat quality in pigs. Genetical Research Cambridge, 55, 33–40. Lopez-Bote, C., Warriss, P. D., & Brown, S. N. (1989). The use of muscle protein solubility measurements to assess pig lean meat quality. Meat Science, 26, 167–175. Lundstro¨m, K., Enfa¨lt, A-C., Tornberg, E., & Agerhem, H. (1998). Sensory and technological meat quality in carriers and non-carriers of the RN allele in Hampshire crosses and in purebred Yorkshire pigs. Meat Science, 48(1/2), 115–124. Lundstro¨m, K., Andersson, A., & Hansson, I. (1996). Effect of the RN gene on technological and sensory meat quality in crossbred pigs with Hampshire as terminal sire. Meat Science, 42(2), 145– 153. MacDougall, D. B. (1982). Changes in the colour and opacity of meat. Food Chemistry, 9, 75–88. Milan, D. J. J., Looft, C., Amarger, V., Robic, A., Thelander, M., Rogel-Gaillard, C., Paul, S., Iannuccelli, N., Rask, L., Ronne, H., Lundstrom, K., Reinsch, N., Gellin, J., Kalm, E., Roy, P. L., Chardon, P., & Andersson, L. (2000). A mutation in PRKAG3 associated with excess glycogen content in pig skeletal muscle. Science, 288(5469), 1248–1251. Miller, K. D., Ellis, M., Bidner, B., McKeith, F. K., & Wilson, E. R. (2000). Porcine Longissimus glycolytic potential level effects on growth performance, carcass, and meat quality characteristics. Journal of Muscle Foods, 11, 169–181. Monin, G., & Sellier, P. (1985). Pork of low technological quality with a normal rate of muscle pH fall in the immediate postmortem period: the case of the Hampshire breed. Meat Science, 13, 49–63. Monin, G., Mejenes-Quijano, A., Talmant, A., & Sellier, P. (1987). Influence of breed and muscle metabolic type on muscle glycolytic potential and meat pH in pigs. Meat Science, 20, 149–158. Naveau, J. (1986). Contribution a l’e´tude du de´terminisme ge´ne´tique de la qualite´ de viande porcine. He´ritabilite´ du Rendemant Technologique NAPOLE. Journe´es de la Recherche Porcine en France, 18, 265–276. NMKL. (1989). Fat. Determination according to SBR (Schmid-Bondzynski-Ratslaff) in meat and meat products. Method No 131, Nordic Committee on Food Analysis. NMKL. (1991). Moisture and ash. Gravimetric determination in meat and meat products. Method No. 23, 3rd ed. Nordic Committee on Food Analysis. Offer, G. (1991). Modelling of the formation of pale, soft and exudative meat: effects of chilling regime and rate and extent of glycolysis. Meat Science, 30, 157–184. Oliver, M. A., Gispert, M., Tibau, J., & Diestre, A. (1991). The measurement of light scattering and electrical conductivity for the prediction of PSE pig meat at various times post-mortem. Meat Science, 29, 141–151. Purchas, R. W., Smith, W. C., & Pearson, G. (1990). A comparison of the Duroc, Hampshire; Landrace, and Large White as terminal sire breeds of crossbred pigs slaughtered at 85 kg liveweight. 2. Meat Quality. New Zealand Journal of Agricultural Research, 33, 97–104. Tornberg, E., Andersson, A. & von Seth, G. (1993). Water distribution in raw pork muscle (M. longissimus dorsi) of different meat

660

A˚. Josell et al. / Meat Science 65 (2003) 651–660

qualities. In Proceedings of the 39th International Congress of Meat Science and Technology. Calgary, Canada. van Laack, R. L. J. M., Stevens, S. G., & Stadler, K. J. (2001). The influence of ultimate pH and intramuscular fat content on pork tenderness and tenderization. Journal of Animal Science, 79, 392–397. van Laack, R. L. J. M., & Kauffman, R. G. (1999). Glycolytic potential of red, soft, exudative pork longissimus muscle. Journal of Animal Science, 77, 2971–2973. Warner, R. D., Kauffman, R. G., & Greaser, M. L. (1997). Muscle

protein changes post mortem in relation to pork quality traits. Meat Science, 45(3), 339–352. Warriss, P. D., Kestin, S. C., Brown, S. N., & Nute, G. R. (1996). The quality of pork from traditional pig breeds. Meat Focus International, May/June, 179–182. Wood, J. D., Brown, S. N., Nute, G. R., Whittington, F. M., Perrry, A. M., Johnson, S. P., & Enser, M. (1996). Effects of breed, feed level and conditioning time on the tenderness of pork. Meat Science, 44(1-2), 105–112.