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Sensory and functional meat quality characteristics of pork derived from three halothane genotypes
Meat Science 63 (2003) 333–338 www.elsevier.com/locate/meatsci
Sensory and functional meat quality characteristics of pork derived from three halothane genotypes E.I. Moelicha, L.C. Hoffmanb,*, P.J. Conradiea a
Department of Consumer Science, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa b Department of Animal Sciences, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa Received 3 September 2001; received in revised form 7 February 2002; accepted 31 March 2002
Abstract The effect of the halothane gene in pigs on the meat and sensory qualities thereof were determined. Meat derived from 60 LandraceLarge White pigs of three halothane genotypes was used. The sensory qualities, cooking loss, colour, shear value and proximate analysis of the cooked pork loin roasts were determined. The three genotypes did not differ significantly (P> 0.05) with regard to the colour of the cooked meat, percentage cooking loss and percentage moisture. There were significant differences (P <0.05) between the genotypes in the percentage protein, ash and fat. Meat from the three genotypes also differed significantly (P< 0.05) in juiciness, an analytical sensory panel scored the juiciness of meat from the NN-genotype the highest with a value of 71.3 when using a structured line scale. Meat from the nn-genotype had the lowest score for juiciness (62.8). Meat from the three genotypes did not differ significantly (P> 0.05) with regard to tenderness, pork flavour and no mealiness. Correlation values showed a positive correlation (r=0.46, P< 0.05) between juiciness and tenderness. These results indicate that the inclusion of the halothane gene in pig production programmes results in meat with an inferior quality and it can be recommended to exclude the halothane positive genotype from any pig production system where fresh pork quality is considered a primary goal. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Halothane genotype; Sensory quality; Pork quality
1. Introduction The consumer demand for lean muscle with less fat has led to the inclusion of the halothane gene in pork production practices. The inclusion of the halothane gene has the advantages of higher feed conversion ratios and greater carcass lean yield but is also associated with higher incidence of the development of the pale, soft and exudative (PSE) condition in meat when these animals are slaughtered. Thus, meeting the objective of increased lean yield has been accompanied by an increased frequency of stress susceptibility and impaired meat quality (Lundstro¨m, Esse´n-Gustavson, Rundgren, Edfors-Lilja, & Malmfors, 1989). PSE meat is characterised by a pale and watery appearance, soft texture and exudation of sarcoplasmic fluid (Bendall &
* Corresponding author. Tel.: +27-21-808-4747; fax: +27-21-8084750. E-mail address: [email protected] (L.C. Hoffman).
Wismer-Pedersen, 1962; Briskey, 1964). The condition is caused by a high rate of glycolysis, resulting in a buildup of lactate, which causes a drop in pH while the muscle temperature is still high (> 35 C) (Mitchell & Heffron, 1982). This decrease in pH causes PSE meat to have a lower water-holding capacity. The development of PSE meat is determined by both genetic and environmental factors (Sather & Murray, 1989). Porcine stress syndrome (PSS) is caused by abnormalities in sarcoplasmic Ca2+ regulation (Mickelson & Louis, 1993). The PSE condition of pork is also related to malignant hyperthermia (MH; Mitchell & Heffron, 1982). Porcine malignant hyperthermia is a genetic defect, which precipitates when the animal is exposed to anaesthetics such as halothane. Pigs most likely to develop MH have a genetic defect caused by an autosomal recessive allele (n), also known as the halothane gene (Sather & Murray, 1989). Halothane positive pigs (nn) react positive to the halothane test. Halothane negative pigs that carry the halothane gene (Nn) display meat of intermediate quality compared with that of
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normal and homozygote pigs (Murray, Jones, & Sather, 1989; Sather, Murray, Zawadski, & Johnson, 1991). Research has also been undertaken to determine the effect of the inclusion of the halothane gene on the sensory properties of the cooked meat. Van Oeckel, Warnants, Boucque´, Delputte, and Depuydt (2001) found no significant difference when consumers compared the tastiness of NN versus Nn meat. Bredahl, Grunert, and Fertin (1998) found that intramuscular fat had a reverse effect on expected and experienced meat quality: higher levels of intramuscular fat reduce consumers expectations of meat quality while it actually contributes positively to tenderness, taste and juiciness. Brewer and McKeith (1999) found that consumers use the colour of fresh pork as an indicator of meat quality with definite discrimination against pork perceived as very light pink (‘‘definitely would not buy’’). This study was undertaken to determine the effect of the halothane gene in pork on colour, sensory qualities (juiciness, tenderness, pork flavour and no mealiness), cooking loss, shear values and proximate analysis of oven roasted pork loins.
2. Materials and methods Sixty LandraceLarge White crosses of the three genotypes (NN=25, Nn=19 and nn=16) were sourced (Fisher, Mellet, & Hoffman, 2000) and raised till a slaughter weight of 86 kg. The production parameters and physical meat quality attributes have been described previously (Fisher et al., 2000). The pigs either originated from a known genotype or were tested for genotype using the method as described by Fujii et al. (1991). The pigs were slaughtered following commercial procedures. The carcasses were chilled at 2 C for 24 h before removal of the different cuts as described by Fisher et al. (2000). The backs from the left side of the carcasses were used for this investigation. The meat was individually wrapped in plastic, coded and frozen at 40 C until completion of the slaughtering process.
removed, all visible fat trimmed, and samples from each cut of meat were used for determining colour, shear values and proximate analysis. The rest of the MLT samples were used for analytical sensory evaluation. 2.2. Cooking loss Individual weights of the cuts were recorded before and after cooking. Cooking loss was expressed as the amount of fluid loss expressed as a percentage of original (wet) weight. Note that the method for determining cooking loss differs from the standard method described by Honikel (1998) for determination of cooking loss in whole meat. 2.3. Colour The CIE Lab colour co-ordinates of each cooked MLT sample were determined using a Colorgard System 2000 colorimeter (Pacific Scientific). The instrument was warmed according to the manufacturer’s instructions (Honikel, 1998) and was calibrated using standard calibrating procedure. Colour measurements (in triplicate) were done on each cooked sample. In the tristimulus system of CIE (Commission International de L’Eclairage), colour is specified in three attributes, namely dominant wavelength, brightness and purity (Penfield & Campbell, 1998). The CIE L-value gives an indication of the lightness (black–white axis), CIE a gives an indication of the redness (red–green spectrum) and CIE b gives an indication of the yellowness (yellow–blue spectrum). 2.4. Warner Bratzler shear force Three 1.27 cm diameter samples from the centre of each cooked MLT sample were randomly removed for determining Warner Bratzler shear force values and were measured as maximum shear force (kg 1.27 cm 1 diameter). Means were calculated for each individual animal. 2.5. Chemical analysis
2.1. Cooking procedure Prior to cooking, the roasts were defrosted for 48 h in a walk-in cooler at a temperature of 3–4 C. All visible skin was removed from the pieces of loin and the subcutaneous fat trimmed to a thickness of 10 mm. The meat was placed on a rack in a roasting pan, fat-side up. A thermocouple was inserted in the centre of each loin and the meat was roasted at 160 C to an internal temperature of 71 C in a conventional electric Defy 835 oven connected to a computerised-temperature control system. The roasts were allowed to cool for 10 min after reaching the desired internal temperature. The pieces of roast were deboned and the M. longissimus dorsi (MLT)
The chemical analysis was done on the minced MLT samples using standard techniques (AOAC, 1997). Moisture content was determined by drying the samples at 100 C for 24 h. Ashing was done at 500 C for 5 h and protein content was calculated (N6.25) after the nitrogen content was determined by the block digestion method using sulphuric acid as digestate. Ether-extractable fat content was determined by solvent extraction. 2.6. Sensory analysis Analytical sensory evaluation by a trained panel of nine panel members was done. The M. longissimus dorsi
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was removed from the cooked samples and cut into 1.51.5 cm cubes. Sensory analysis was done directly after completion of the cooking procedure. The meat was cooked and the samples were evaluated in 14 sessions over a period of five days using an unstructured line scale (0–100 mm), where a score of 0=very low in the mentioned attribute and 100=very high. Judges were trained to evaluate the attributes of juiciness, tenderness, no mealiness and pork flavour on a questionnaire compiled and refined by the panel during the training sessions. Meat from the three genotypes was randomly served to each panel member in heated Pyrex beakers coded with a three digit random code. Verbal definitions as decided on by the panel during the training session are described in Table 1. 2.7. Statistical analysis The effect of genotype on cooking loss, colour, shear force values, moisture, protein, ash and fat content were evaluated by factorial analysis of variance using SAS (Statistical Analysis System Institute, 1990). The Shapiro–Wilk test was performed to test for non-normality (Shapiro & Wilk, 1965). Student’s t-least significant difference was calculated at a 5% significance level to compare treatment means of significant effects. Analysis of variance was performed on the variables of the sensory analysis using the general linear models (GLM) procedure of SAS (1990). All values were used in the statistical analysis. The sensory analysis consisted of six treatment combinations, each replicated 16 times by nine panel members in a completely randomised design. The treatment combinations involved a 123 factorial array arising from the combination of one cooking method (roasted pork loin), two sexes (barrows and gilts) and three genotypes (NN, Nn and nn). An effect with probability smaller than 0.05 (P < 0.05) is considered as significant. Pearson correlation coefficients was determined using SAS (1990).
3. Results and discussion 3.1. Colour No significant difference (P > 0.05) in the CIE Lab values (L, a, b) of the cooked meat from the three genotypes were found (Table 2). Results by Fisher et al. (2000), who did work on the same carcasses, indicated that the reflectance values of fresh meat from the three genotypes differed significantly (P < 0.05). Meat from the nn genotype had the highest mean reflectance value (L=45.8), indicating paler meat compared to both the Nn (L=43.5) and NN (L=41.9) genotypes. The phenomenon that the present investigation did not show significant differences in the reflectance values could be
Table 1 Definitions of terms used in the sensory analysis of pork loin roasts Attribute
Attribute definition
Juiciness
Degree of moisture inside the sample released upon chewing
Tenderness
Force required to compress the sample of meat between molar teeth on the first bite
Pork flavour
A flavour associated with cooked pork meat
No mealiness
Consistency of sample after chewing, degree of disintegration of fibres (no mealiness=100)
due to the fact that the values were all conducted on cooked meat. All the research results cited are for reflectance values determined on fresh pork. Colour measurements of fresh meat showed meat from nn and Nn pigs had significant higher CIE L-reflectance values than NN pigs, suggesting Nn and nn pigs have palercoloured meat (De Smet, Bloemen, van de Voorde, Spincemaille, & Berckmans, 1998; Esse´n-Gustavson, Karlstro¨m, & Lundstro¨m, 1992; Sather et al., 1991; Van Oeckel et al., 2001). Pommier and Houde (1993) and Murray et al. (1989) also found nn meat to be paler than Nn and NN meat when comparing CIE L values of fresh meat. Higher L values are associated with an increase in light scattering (Bendall, 1973) due to the open structure of PSE meat (Lawrie, 1991). The colour changes in PSE meat are a result of abnormal pH values and water-holding capacity (Barton-Gade, Cross, Jones, & Winger, 1988). According to Brewer and McKeith (1999) consumers discriminate against pork being perceived as ‘‘very light pink’’. Jeremiah (1994) also found that consumers discriminate against PSE chops. Consumers use the colour of meat, as a quality indicator and paler meat are associated with the PSE condition and meat of a lower quality. 3.2. Physical characteristics The percentage cooking loss (% CL) did not differ significantly (P > 0.05) between the three genotypes (Table 2), although meat from the Nn (27.6%) and nn (27.7%) genotypes had a higher percentage cooking loss than meat from the NN (26.8%) genotype. Fisher et al. (2000), using meat from the same carcasses but a different method of determining cooking loss, found mean cooking loss to be the highest for meat originating from the nn genotypes (28.2%), differing significantly (P < 0.001) from the NN (25.6%) and the Nn (26.4%) genotypes. Results from Stalder, Maya, Christian, Moeller, and Prusa (1998) indicated a similar pattern with no significant difference in% CL between NN and nn meat. De Smet et al. (1998) found cooking loss to be lower for the nn genotype compared to the NN genotype (P < 0.01), whereas there were no differences
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Table 2 The effect of pig genotype on meat quality characteristics of cooked pork (meansSE)a Characteristic
L a b Cooking loss (%) Warner-Bratzler (kg/1.27 cm ) Moisture (% as is) Fat (% of dry matter) Protein (% of dry matter) Ash (% of dry matter) a
Genotype NN
Nn
nn
P >F
72.30.324 2.10.141 14.30.145 26.80.765 3.0a0.063 58.80.723 17.0d1.779 71.2a1.743 6.4a0.565
71.60.483 2.00.189 14.20.123 27.60.849 3.1ab0.090 59.70.588 14.4d1.158 74.1a1.101 7.7ab0.563
72.30.430 2.10.232 14.20.138 27.70.917 3.2b0.093 60.10.736 8.3e0.791 78.2b0.710 7.9b0.650
0.346 0.685 0.715 0.249 0.060 0.448 0.002 0.001 0.109
Values in the same row with different letters differ significantly at the P <0.05 level (a,b) or at the P <0.001 level (d,e).
between the NN and Nn genotypes (P > 0.05). Results from an investigation by Van Oeckel et al. (2001) found higher% cooking losses for NN meat compared to Nn meat. Shear force values of meat samples from the nn group (3.18 kg 1.27 cm 1Ø) were significantly higher (P < 0.05) than those of the NN-group (2.96 kg 1.27 cm 1Ø, Table 2). Both of these did not differ significantly (P > 0.05) from the Nn-group (3.12 kg 1.27 cm 1Ø). Fisher et al. (2000), using material from the same carcasses but a different cooking method (Honikel, 1987), found the highest shear values for meat from the Nn genotype (3.35 kg/1.27 cm) with nn values intermediate (3.11 kg/1.27 cm) and NN values the lowest (2.92 kg/ 1.27 cm). Values for NN and Nn samples differed significantly (P < 0.001). Results from this investigation are in accordance to that of Murray et al. (1989) who found that the shear value of the nn genotype was higher than that of the NN genotype; the Nn genotype was intermediate or closer to the nn genotype. Research done by Stalder et al. (1998) indicated a similar pattern with the shear values of broiled chops from the nn genotype being significantly higher than that of the NN genotype. Results from Van Oeckel et al. (2001) for shear values indicated that Nn meat had a lower shear value than NN meat and was therefore more tender. 3.3. Chemical composition There was no significant difference between the three genotypes with regard to percentage moisture of the cooked samples (Table 2). The fat content, expressed as % fat on a dry matter basis, differed significantly between meat from the NN and nn pigs (P < 0.001), but not between meat from the NN and Nn pigs. The mean percentage muscle fat of meat from the three genotypes was NN=17.1%, Nn=14.4% and nn=8.3%. The protein content of the nn pigs was 78.2%, significantly higher (P < 0.05) than that of the NN (74.1%) and Nn (74.1%) pigs. The latter two groups did not differ
significantly (P > 0.05). Pigs from the NN group had a significantly lower (P < 0.05) ash content (6.4%) than that of the nn (7.9%) group (Table 2). Both of these did not differ significantly from the Nn group (7.7%). Monin et al. (1999) found that cooked meat from NN pigs contained more moisture than that from nn pigs. Murray et al. (1989) found fat content to be lower and protein and moisture content of muscle from the nn genotype to be higher than that of the NN genotype, similar to the results of this investigation. Meat from the nn genotype has a higher lean muscle content as well as a decreased carcass and lean muscle fat content. 3.4. Analytical sensory evaluation A trained laboratory panel was asked to evaluate the meat representing the three genotypes with regard to juiciness, tenderness, pork flavour and no mealiness. The juiciness of meat from the three genotypes differed significantly (P < 0.05) with the NN-group having the highest score for juiciness (71.3) and the nn-group the lowest (62.8), Table 3. The difference in juiciness could be a due to structural differences. Fisher et al. (2000) found 8% of the NN carcasses, 42% of the Nn carcasses and 100% of the nn carcasses to be classified with the PSE condition (pH45 < 5.9). The results for juiciness also confirm the results of fat content and % cooking loss. The NN-group had a significantly higher (P < 0.001) fat content than the nn-group and a lower % cooking loss. During cooking, the fat content of the lean increases as a result of surface fat that melts and penetrates the lean muscle, and the meat is perceived as being more juicy (Bredahl et al., 1998). The results for juiciness is in accordance with the results of Fox, Wolfram Kemp, and Langlois (1980) who found PSE chops were consistently rated lower for juiciness when compared with normal chops by a sensory panel (P < 0.01). Juiciness is the eating characteristic of meat which is most affected by a reduction in fat proportion, thus inclusion of the halothane gene to produce meat with a higher proportion
E.I. Moelich et al. / Meat Science 63 (2003) 333–338 Table 3 The effect of pig genotype on the sensory quality of cooked pork (meansSE)a Attribute
Juiciness Tenderness Pork flavour No mealiness
Genotype NN
Nn
nn
P> F
71.3a1.993 84.31.303 76.72.098 66.12.483
65.1b2.169 83.4 1.346 78.7 1.896 65.2 2.616
62.8c2.224 83.91.348 79.71.757 58.32.848
0.015 0.825 0.411 0.090
a
Values in the same row with different letters differ significantly (P<0.05).
of lean and lower fat, will have a negative impact on the eating quality of the meat, and specifically the juiciness. Results by Monin et al. (1999) showed meat from nn pigs have lower roughness, higher cohesiveness, higher initial hardness and fibrousness, lower granularity, higher elasticity, higher sustained hardness and fibrousness, and lower sustained granularity than meat from the NN and Nn pigs. Meat from the nn pigs was more difficult to swallow than meat from NN pigs. Monin et al. (1999) found the effect of the halothane gene to be detrimental to meat acceptance. Meat from the three genotypes did not differ significantly (P > 0.05) in tenderness (Table 3). The mean tenderness value was however lower in the nn group (83.8) than in the NN-group (84.3). Comparison of values for tenderness as measured by the Warner-Bratzler; show the same tendency, with meat from the nngroup having significantly higher (thus less tender) values (3.18 kg 1.27 cm 1Ø) than meat from the NNgroup (2.96 kg 1.27 cm 1Ø). The results of this investigation are in accordance with that of Fox et al. (1980) who found no significant difference in taste panel tenderness scores when comparing normal and PSE pork chops, although juiciness differed significantly. The panel could not detect any significant differences in pork flavour between the three genotypes (Table 3). Fox et al. (1980) found panel members scored normal chops higher for flavour when compared to the PSE chops, although no significant differences in cooked aroma between the quality groups could be detected. Results of Leach, Ellis, Sutton, McKeith, and Wilson (1996) showed no significant difference between Nn and NN meat when a trained panel evaluated the juiciness, tenderness and off-flavour of the cooked meat. The analytical sensory panel defined no mealiness as a measure of the consistency of the sample after chewing, an indication of the degree of disintegration of fibres. Meat from the nn genotype was evaluated as being mealier than meat from the NN and the Nn genotypes; these differences were not significant (P > 0.05) however. This corresponds with the results for juiciness and fat content where meat from the NN-group was juicier and had a higher % fat than meat from the nn group.
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3.5. Relationships between variables Comparison of correlation values shows a significant (P < 0.05) inverse correlation (r= 0.493) between tenderness and shear force values for the pooled sensory data. A significant inverse correlation (P < 0.05) was also found between tenderness and shear force for meat from the NN (r= 0.621) and Nn (r= 0.562) genotypes. No significant correlation between tenderness and shear force for meat from the nn genotype was found. A positive correlation was calculated between the percentage cooking loss and shear force (r=0.58, P < 0.0001) and a negative correlation between percent fat and shear force (r= 0.56, P < 0.0001). Thus a higher percentage cooking loss and lower percentage intramuscular fat would imply a higher shear force value and thus tougher meat. Comparison of the % CL and % fat indicates that meat from the nn carcasses have the highest % CL (although not significant) and lowest % fat. Meat with a low percentage of intramuscular fat has a lower water holding capacity, and if this were combined with the low pH values of the PSE condition, it would result in higher cooking losses. In this investigation, all of the nn carcasses are considered as PSE and meat from the nn carcasses had a significantly lower (P < 0.001) % fat compared with the Nn and NN meat. Again this shows that the inclusion of the halothane gene in pork production practices leads to meat with an inferior quality. When determining correlation values for the pooled data, a positive correlation (P < 0.05) between juiciness and tenderness (r=0.46), no mealiness (r=0.66) and pork flavour (r=0.52) was found. This implies that meat that was rated high for juiciness, was also rated high for tenderness, no mealiness and pork flavour.
4. Conclusions The percentage cooking loss did not differ significantly between the three genotypes. Genotype had a significant influence on shear value with meat from nn carcasses having the highest values (3.18 kg 1.27 cm 1Ø) and meat from the NN carcasses the lowest (2.96 kg 1.27 cm 1Ø). The percentage fat (calculated as percentage of dry matter) was significantly lower (P< 0.001) in nn meat (8.3%) than in Nn (14.4%) and NN (17.1%) meat. The percentage protein was significantly higher (P< 0.05) in nn meat compared with Nn and NN meat. The results of the analytical sensory analysis indicated that the three genotypes differed significantly (P< 0.05) with regard to juiciness with meat from the nn genotype having the lowest scores for juiciness. The inclusion of the halothane gene in pig production programs have the potential to produce carcasses with a higher lean tissue content as well as muscle with a higher protein content and lower fat content (Wood,
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Gregory, Hall, & Lister, 1977). Yet, pigs with the nn and Nn genotypes are more susceptible to stress and thus the production of poor quality meat (Stalder et al., 1998) with a paler colour, higher cooking losses and higher shear values (Murray et al., 1989; Sather et al., 1991). Results from this investigation are in accordance with those mentioned above. Consumers show a growing interest in meat quality with colour as an important aspect influencing consumer acceptability (Demos, Garrard, Mandigo, Gao, & Tan, 1996). The inclusion of the halothane gene in pig production programs would result in lower quality of fresh and cooked meat from the carcasses of the nn and Nn genotype pigs.
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Sensory and functional meat quality characteristics of pork derived from three halothane genotypes E.I. Moelicha, L.C. Hoffmanb,*, P.J. Conradiea a
Department of Consumer Science, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa b Department of Animal Sciences, Stellenbosch University, Private Bag X1, Matieland 7602, South Africa Received 3 September 2001; received in revised form 7 February 2002; accepted 31 March 2002
Abstract The effect of the halothane gene in pigs on the meat and sensory qualities thereof were determined. Meat derived from 60 LandraceLarge White pigs of three halothane genotypes was used. The sensory qualities, cooking loss, colour, shear value and proximate analysis of the cooked pork loin roasts were determined. The three genotypes did not differ significantly (P> 0.05) with regard to the colour of the cooked meat, percentage cooking loss and percentage moisture. There were significant differences (P <0.05) between the genotypes in the percentage protein, ash and fat. Meat from the three genotypes also differed significantly (P< 0.05) in juiciness, an analytical sensory panel scored the juiciness of meat from the NN-genotype the highest with a value of 71.3 when using a structured line scale. Meat from the nn-genotype had the lowest score for juiciness (62.8). Meat from the three genotypes did not differ significantly (P> 0.05) with regard to tenderness, pork flavour and no mealiness. Correlation values showed a positive correlation (r=0.46, P< 0.05) between juiciness and tenderness. These results indicate that the inclusion of the halothane gene in pig production programmes results in meat with an inferior quality and it can be recommended to exclude the halothane positive genotype from any pig production system where fresh pork quality is considered a primary goal. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Halothane genotype; Sensory quality; Pork quality
1. Introduction The consumer demand for lean muscle with less fat has led to the inclusion of the halothane gene in pork production practices. The inclusion of the halothane gene has the advantages of higher feed conversion ratios and greater carcass lean yield but is also associated with higher incidence of the development of the pale, soft and exudative (PSE) condition in meat when these animals are slaughtered. Thus, meeting the objective of increased lean yield has been accompanied by an increased frequency of stress susceptibility and impaired meat quality (Lundstro¨m, Esse´n-Gustavson, Rundgren, Edfors-Lilja, & Malmfors, 1989). PSE meat is characterised by a pale and watery appearance, soft texture and exudation of sarcoplasmic fluid (Bendall &
* Corresponding author. Tel.: +27-21-808-4747; fax: +27-21-8084750. E-mail address: [email protected] (L.C. Hoffman).
Wismer-Pedersen, 1962; Briskey, 1964). The condition is caused by a high rate of glycolysis, resulting in a buildup of lactate, which causes a drop in pH while the muscle temperature is still high (> 35 C) (Mitchell & Heffron, 1982). This decrease in pH causes PSE meat to have a lower water-holding capacity. The development of PSE meat is determined by both genetic and environmental factors (Sather & Murray, 1989). Porcine stress syndrome (PSS) is caused by abnormalities in sarcoplasmic Ca2+ regulation (Mickelson & Louis, 1993). The PSE condition of pork is also related to malignant hyperthermia (MH; Mitchell & Heffron, 1982). Porcine malignant hyperthermia is a genetic defect, which precipitates when the animal is exposed to anaesthetics such as halothane. Pigs most likely to develop MH have a genetic defect caused by an autosomal recessive allele (n), also known as the halothane gene (Sather & Murray, 1989). Halothane positive pigs (nn) react positive to the halothane test. Halothane negative pigs that carry the halothane gene (Nn) display meat of intermediate quality compared with that of
0309-1740/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0309-1740(02)00090-6
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normal and homozygote pigs (Murray, Jones, & Sather, 1989; Sather, Murray, Zawadski, & Johnson, 1991). Research has also been undertaken to determine the effect of the inclusion of the halothane gene on the sensory properties of the cooked meat. Van Oeckel, Warnants, Boucque´, Delputte, and Depuydt (2001) found no significant difference when consumers compared the tastiness of NN versus Nn meat. Bredahl, Grunert, and Fertin (1998) found that intramuscular fat had a reverse effect on expected and experienced meat quality: higher levels of intramuscular fat reduce consumers expectations of meat quality while it actually contributes positively to tenderness, taste and juiciness. Brewer and McKeith (1999) found that consumers use the colour of fresh pork as an indicator of meat quality with definite discrimination against pork perceived as very light pink (‘‘definitely would not buy’’). This study was undertaken to determine the effect of the halothane gene in pork on colour, sensory qualities (juiciness, tenderness, pork flavour and no mealiness), cooking loss, shear values and proximate analysis of oven roasted pork loins.
2. Materials and methods Sixty LandraceLarge White crosses of the three genotypes (NN=25, Nn=19 and nn=16) were sourced (Fisher, Mellet, & Hoffman, 2000) and raised till a slaughter weight of 86 kg. The production parameters and physical meat quality attributes have been described previously (Fisher et al., 2000). The pigs either originated from a known genotype or were tested for genotype using the method as described by Fujii et al. (1991). The pigs were slaughtered following commercial procedures. The carcasses were chilled at 2 C for 24 h before removal of the different cuts as described by Fisher et al. (2000). The backs from the left side of the carcasses were used for this investigation. The meat was individually wrapped in plastic, coded and frozen at 40 C until completion of the slaughtering process.
removed, all visible fat trimmed, and samples from each cut of meat were used for determining colour, shear values and proximate analysis. The rest of the MLT samples were used for analytical sensory evaluation. 2.2. Cooking loss Individual weights of the cuts were recorded before and after cooking. Cooking loss was expressed as the amount of fluid loss expressed as a percentage of original (wet) weight. Note that the method for determining cooking loss differs from the standard method described by Honikel (1998) for determination of cooking loss in whole meat. 2.3. Colour The CIE Lab colour co-ordinates of each cooked MLT sample were determined using a Colorgard System 2000 colorimeter (Pacific Scientific). The instrument was warmed according to the manufacturer’s instructions (Honikel, 1998) and was calibrated using standard calibrating procedure. Colour measurements (in triplicate) were done on each cooked sample. In the tristimulus system of CIE (Commission International de L’Eclairage), colour is specified in three attributes, namely dominant wavelength, brightness and purity (Penfield & Campbell, 1998). The CIE L-value gives an indication of the lightness (black–white axis), CIE a gives an indication of the redness (red–green spectrum) and CIE b gives an indication of the yellowness (yellow–blue spectrum). 2.4. Warner Bratzler shear force Three 1.27 cm diameter samples from the centre of each cooked MLT sample were randomly removed for determining Warner Bratzler shear force values and were measured as maximum shear force (kg 1.27 cm 1 diameter). Means were calculated for each individual animal. 2.5. Chemical analysis
2.1. Cooking procedure Prior to cooking, the roasts were defrosted for 48 h in a walk-in cooler at a temperature of 3–4 C. All visible skin was removed from the pieces of loin and the subcutaneous fat trimmed to a thickness of 10 mm. The meat was placed on a rack in a roasting pan, fat-side up. A thermocouple was inserted in the centre of each loin and the meat was roasted at 160 C to an internal temperature of 71 C in a conventional electric Defy 835 oven connected to a computerised-temperature control system. The roasts were allowed to cool for 10 min after reaching the desired internal temperature. The pieces of roast were deboned and the M. longissimus dorsi (MLT)
The chemical analysis was done on the minced MLT samples using standard techniques (AOAC, 1997). Moisture content was determined by drying the samples at 100 C for 24 h. Ashing was done at 500 C for 5 h and protein content was calculated (N6.25) after the nitrogen content was determined by the block digestion method using sulphuric acid as digestate. Ether-extractable fat content was determined by solvent extraction. 2.6. Sensory analysis Analytical sensory evaluation by a trained panel of nine panel members was done. The M. longissimus dorsi
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was removed from the cooked samples and cut into 1.51.5 cm cubes. Sensory analysis was done directly after completion of the cooking procedure. The meat was cooked and the samples were evaluated in 14 sessions over a period of five days using an unstructured line scale (0–100 mm), where a score of 0=very low in the mentioned attribute and 100=very high. Judges were trained to evaluate the attributes of juiciness, tenderness, no mealiness and pork flavour on a questionnaire compiled and refined by the panel during the training sessions. Meat from the three genotypes was randomly served to each panel member in heated Pyrex beakers coded with a three digit random code. Verbal definitions as decided on by the panel during the training session are described in Table 1. 2.7. Statistical analysis The effect of genotype on cooking loss, colour, shear force values, moisture, protein, ash and fat content were evaluated by factorial analysis of variance using SAS (Statistical Analysis System Institute, 1990). The Shapiro–Wilk test was performed to test for non-normality (Shapiro & Wilk, 1965). Student’s t-least significant difference was calculated at a 5% significance level to compare treatment means of significant effects. Analysis of variance was performed on the variables of the sensory analysis using the general linear models (GLM) procedure of SAS (1990). All values were used in the statistical analysis. The sensory analysis consisted of six treatment combinations, each replicated 16 times by nine panel members in a completely randomised design. The treatment combinations involved a 123 factorial array arising from the combination of one cooking method (roasted pork loin), two sexes (barrows and gilts) and three genotypes (NN, Nn and nn). An effect with probability smaller than 0.05 (P < 0.05) is considered as significant. Pearson correlation coefficients was determined using SAS (1990).
3. Results and discussion 3.1. Colour No significant difference (P > 0.05) in the CIE Lab values (L, a, b) of the cooked meat from the three genotypes were found (Table 2). Results by Fisher et al. (2000), who did work on the same carcasses, indicated that the reflectance values of fresh meat from the three genotypes differed significantly (P < 0.05). Meat from the nn genotype had the highest mean reflectance value (L=45.8), indicating paler meat compared to both the Nn (L=43.5) and NN (L=41.9) genotypes. The phenomenon that the present investigation did not show significant differences in the reflectance values could be
Table 1 Definitions of terms used in the sensory analysis of pork loin roasts Attribute
Attribute definition
Juiciness
Degree of moisture inside the sample released upon chewing
Tenderness
Force required to compress the sample of meat between molar teeth on the first bite
Pork flavour
A flavour associated with cooked pork meat
No mealiness
Consistency of sample after chewing, degree of disintegration of fibres (no mealiness=100)
due to the fact that the values were all conducted on cooked meat. All the research results cited are for reflectance values determined on fresh pork. Colour measurements of fresh meat showed meat from nn and Nn pigs had significant higher CIE L-reflectance values than NN pigs, suggesting Nn and nn pigs have palercoloured meat (De Smet, Bloemen, van de Voorde, Spincemaille, & Berckmans, 1998; Esse´n-Gustavson, Karlstro¨m, & Lundstro¨m, 1992; Sather et al., 1991; Van Oeckel et al., 2001). Pommier and Houde (1993) and Murray et al. (1989) also found nn meat to be paler than Nn and NN meat when comparing CIE L values of fresh meat. Higher L values are associated with an increase in light scattering (Bendall, 1973) due to the open structure of PSE meat (Lawrie, 1991). The colour changes in PSE meat are a result of abnormal pH values and water-holding capacity (Barton-Gade, Cross, Jones, & Winger, 1988). According to Brewer and McKeith (1999) consumers discriminate against pork being perceived as ‘‘very light pink’’. Jeremiah (1994) also found that consumers discriminate against PSE chops. Consumers use the colour of meat, as a quality indicator and paler meat are associated with the PSE condition and meat of a lower quality. 3.2. Physical characteristics The percentage cooking loss (% CL) did not differ significantly (P > 0.05) between the three genotypes (Table 2), although meat from the Nn (27.6%) and nn (27.7%) genotypes had a higher percentage cooking loss than meat from the NN (26.8%) genotype. Fisher et al. (2000), using meat from the same carcasses but a different method of determining cooking loss, found mean cooking loss to be the highest for meat originating from the nn genotypes (28.2%), differing significantly (P < 0.001) from the NN (25.6%) and the Nn (26.4%) genotypes. Results from Stalder, Maya, Christian, Moeller, and Prusa (1998) indicated a similar pattern with no significant difference in% CL between NN and nn meat. De Smet et al. (1998) found cooking loss to be lower for the nn genotype compared to the NN genotype (P < 0.01), whereas there were no differences
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Table 2 The effect of pig genotype on meat quality characteristics of cooked pork (meansSE)a Characteristic
L a b Cooking loss (%) Warner-Bratzler (kg/1.27 cm ) Moisture (% as is) Fat (% of dry matter) Protein (% of dry matter) Ash (% of dry matter) a
Genotype NN
Nn
nn
P >F
72.30.324 2.10.141 14.30.145 26.80.765 3.0a0.063 58.80.723 17.0d1.779 71.2a1.743 6.4a0.565
71.60.483 2.00.189 14.20.123 27.60.849 3.1ab0.090 59.70.588 14.4d1.158 74.1a1.101 7.7ab0.563
72.30.430 2.10.232 14.20.138 27.70.917 3.2b0.093 60.10.736 8.3e0.791 78.2b0.710 7.9b0.650
0.346 0.685 0.715 0.249 0.060 0.448 0.002 0.001 0.109
Values in the same row with different letters differ significantly at the P <0.05 level (a,b) or at the P <0.001 level (d,e).
between the NN and Nn genotypes (P > 0.05). Results from an investigation by Van Oeckel et al. (2001) found higher% cooking losses for NN meat compared to Nn meat. Shear force values of meat samples from the nn group (3.18 kg 1.27 cm 1Ø) were significantly higher (P < 0.05) than those of the NN-group (2.96 kg 1.27 cm 1Ø, Table 2). Both of these did not differ significantly (P > 0.05) from the Nn-group (3.12 kg 1.27 cm 1Ø). Fisher et al. (2000), using material from the same carcasses but a different cooking method (Honikel, 1987), found the highest shear values for meat from the Nn genotype (3.35 kg/1.27 cm) with nn values intermediate (3.11 kg/1.27 cm) and NN values the lowest (2.92 kg/ 1.27 cm). Values for NN and Nn samples differed significantly (P < 0.001). Results from this investigation are in accordance to that of Murray et al. (1989) who found that the shear value of the nn genotype was higher than that of the NN genotype; the Nn genotype was intermediate or closer to the nn genotype. Research done by Stalder et al. (1998) indicated a similar pattern with the shear values of broiled chops from the nn genotype being significantly higher than that of the NN genotype. Results from Van Oeckel et al. (2001) for shear values indicated that Nn meat had a lower shear value than NN meat and was therefore more tender. 3.3. Chemical composition There was no significant difference between the three genotypes with regard to percentage moisture of the cooked samples (Table 2). The fat content, expressed as % fat on a dry matter basis, differed significantly between meat from the NN and nn pigs (P < 0.001), but not between meat from the NN and Nn pigs. The mean percentage muscle fat of meat from the three genotypes was NN=17.1%, Nn=14.4% and nn=8.3%. The protein content of the nn pigs was 78.2%, significantly higher (P < 0.05) than that of the NN (74.1%) and Nn (74.1%) pigs. The latter two groups did not differ
significantly (P > 0.05). Pigs from the NN group had a significantly lower (P < 0.05) ash content (6.4%) than that of the nn (7.9%) group (Table 2). Both of these did not differ significantly from the Nn group (7.7%). Monin et al. (1999) found that cooked meat from NN pigs contained more moisture than that from nn pigs. Murray et al. (1989) found fat content to be lower and protein and moisture content of muscle from the nn genotype to be higher than that of the NN genotype, similar to the results of this investigation. Meat from the nn genotype has a higher lean muscle content as well as a decreased carcass and lean muscle fat content. 3.4. Analytical sensory evaluation A trained laboratory panel was asked to evaluate the meat representing the three genotypes with regard to juiciness, tenderness, pork flavour and no mealiness. The juiciness of meat from the three genotypes differed significantly (P < 0.05) with the NN-group having the highest score for juiciness (71.3) and the nn-group the lowest (62.8), Table 3. The difference in juiciness could be a due to structural differences. Fisher et al. (2000) found 8% of the NN carcasses, 42% of the Nn carcasses and 100% of the nn carcasses to be classified with the PSE condition (pH45 < 5.9). The results for juiciness also confirm the results of fat content and % cooking loss. The NN-group had a significantly higher (P < 0.001) fat content than the nn-group and a lower % cooking loss. During cooking, the fat content of the lean increases as a result of surface fat that melts and penetrates the lean muscle, and the meat is perceived as being more juicy (Bredahl et al., 1998). The results for juiciness is in accordance with the results of Fox, Wolfram Kemp, and Langlois (1980) who found PSE chops were consistently rated lower for juiciness when compared with normal chops by a sensory panel (P < 0.01). Juiciness is the eating characteristic of meat which is most affected by a reduction in fat proportion, thus inclusion of the halothane gene to produce meat with a higher proportion
E.I. Moelich et al. / Meat Science 63 (2003) 333–338 Table 3 The effect of pig genotype on the sensory quality of cooked pork (meansSE)a Attribute
Juiciness Tenderness Pork flavour No mealiness
Genotype NN
Nn
nn
P> F
71.3a1.993 84.31.303 76.72.098 66.12.483
65.1b2.169 83.4 1.346 78.7 1.896 65.2 2.616
62.8c2.224 83.91.348 79.71.757 58.32.848
0.015 0.825 0.411 0.090
a
Values in the same row with different letters differ significantly (P<0.05).
of lean and lower fat, will have a negative impact on the eating quality of the meat, and specifically the juiciness. Results by Monin et al. (1999) showed meat from nn pigs have lower roughness, higher cohesiveness, higher initial hardness and fibrousness, lower granularity, higher elasticity, higher sustained hardness and fibrousness, and lower sustained granularity than meat from the NN and Nn pigs. Meat from the nn pigs was more difficult to swallow than meat from NN pigs. Monin et al. (1999) found the effect of the halothane gene to be detrimental to meat acceptance. Meat from the three genotypes did not differ significantly (P > 0.05) in tenderness (Table 3). The mean tenderness value was however lower in the nn group (83.8) than in the NN-group (84.3). Comparison of values for tenderness as measured by the Warner-Bratzler; show the same tendency, with meat from the nngroup having significantly higher (thus less tender) values (3.18 kg 1.27 cm 1Ø) than meat from the NNgroup (2.96 kg 1.27 cm 1Ø). The results of this investigation are in accordance with that of Fox et al. (1980) who found no significant difference in taste panel tenderness scores when comparing normal and PSE pork chops, although juiciness differed significantly. The panel could not detect any significant differences in pork flavour between the three genotypes (Table 3). Fox et al. (1980) found panel members scored normal chops higher for flavour when compared to the PSE chops, although no significant differences in cooked aroma between the quality groups could be detected. Results of Leach, Ellis, Sutton, McKeith, and Wilson (1996) showed no significant difference between Nn and NN meat when a trained panel evaluated the juiciness, tenderness and off-flavour of the cooked meat. The analytical sensory panel defined no mealiness as a measure of the consistency of the sample after chewing, an indication of the degree of disintegration of fibres. Meat from the nn genotype was evaluated as being mealier than meat from the NN and the Nn genotypes; these differences were not significant (P > 0.05) however. This corresponds with the results for juiciness and fat content where meat from the NN-group was juicier and had a higher % fat than meat from the nn group.
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3.5. Relationships between variables Comparison of correlation values shows a significant (P < 0.05) inverse correlation (r= 0.493) between tenderness and shear force values for the pooled sensory data. A significant inverse correlation (P < 0.05) was also found between tenderness and shear force for meat from the NN (r= 0.621) and Nn (r= 0.562) genotypes. No significant correlation between tenderness and shear force for meat from the nn genotype was found. A positive correlation was calculated between the percentage cooking loss and shear force (r=0.58, P < 0.0001) and a negative correlation between percent fat and shear force (r= 0.56, P < 0.0001). Thus a higher percentage cooking loss and lower percentage intramuscular fat would imply a higher shear force value and thus tougher meat. Comparison of the % CL and % fat indicates that meat from the nn carcasses have the highest % CL (although not significant) and lowest % fat. Meat with a low percentage of intramuscular fat has a lower water holding capacity, and if this were combined with the low pH values of the PSE condition, it would result in higher cooking losses. In this investigation, all of the nn carcasses are considered as PSE and meat from the nn carcasses had a significantly lower (P < 0.001) % fat compared with the Nn and NN meat. Again this shows that the inclusion of the halothane gene in pork production practices leads to meat with an inferior quality. When determining correlation values for the pooled data, a positive correlation (P < 0.05) between juiciness and tenderness (r=0.46), no mealiness (r=0.66) and pork flavour (r=0.52) was found. This implies that meat that was rated high for juiciness, was also rated high for tenderness, no mealiness and pork flavour.
4. Conclusions The percentage cooking loss did not differ significantly between the three genotypes. Genotype had a significant influence on shear value with meat from nn carcasses having the highest values (3.18 kg 1.27 cm 1Ø) and meat from the NN carcasses the lowest (2.96 kg 1.27 cm 1Ø). The percentage fat (calculated as percentage of dry matter) was significantly lower (P< 0.001) in nn meat (8.3%) than in Nn (14.4%) and NN (17.1%) meat. The percentage protein was significantly higher (P< 0.05) in nn meat compared with Nn and NN meat. The results of the analytical sensory analysis indicated that the three genotypes differed significantly (P< 0.05) with regard to juiciness with meat from the nn genotype having the lowest scores for juiciness. The inclusion of the halothane gene in pig production programs have the potential to produce carcasses with a higher lean tissue content as well as muscle with a higher protein content and lower fat content (Wood,
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Gregory, Hall, & Lister, 1977). Yet, pigs with the nn and Nn genotypes are more susceptible to stress and thus the production of poor quality meat (Stalder et al., 1998) with a paler colour, higher cooking losses and higher shear values (Murray et al., 1989; Sather et al., 1991). Results from this investigation are in accordance with those mentioned above. Consumers show a growing interest in meat quality with colour as an important aspect influencing consumer acceptability (Demos, Garrard, Mandigo, Gao, & Tan, 1996). The inclusion of the halothane gene in pig production programs would result in lower quality of fresh and cooked meat from the carcasses of the nn and Nn genotype pigs.
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