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Fatty acid composition of lipid in Longissimus dorsi muscle of Duroc and British Landrace pigs and its relationship with eating quality
Meat Science 29 (1991) 295-307
Fatty Acid Composition of Lipid in Longissimus Dorsi Muscle of Duroc and British Landrace Pigs and its Relationship with Eating Quality
N. D. Cameron AFRC Institute of Animal Physiology and Genetics Research, Edinburgh Research Station, Roslin, Midlothian, EH25 9PS, Scotland
& M. B. Enser AFRC Institute of Food Research, Bristol Laboratory, Langford, Bristol, BSI8 7DY, England (Received 3 May 1990; revised version received 10 June 1990; accepted 18 June 1990)
ABSTRACT The fatty acid composition of intramuscular fat from Duroc and halothane negative British Landrace pigs was determined and the relationships between fatty acid concentrations and aspects of eating quality were estimated from data on 160 pigs. Boars and gilts from each breed were performance tested on ad libitum or restricted feeding regimes with an average slaughter weight of 80 kg. Eating quality was assessed by ten experienced taste panelists. Intramuscular fat of Duroc pigs had higher concentrations of saturated and mono-unsaturated fatty acids and lower concentrations of poly-unsaturated fatty acids than Landrace pigs. With increasing intramuscular fat content, concentrations of saturated and mono-unsaturated fatty acids increased and concentrations of poly-unsaturated fatty acids decreased and the rate of change in fatty acid concentrations was greater in Landrace pigs than in Duroc pigs. Eating quality traits were generally improved as the concentration of mono-unsaturated fatty acids increased and poly-unsaturated fatty acids decreased. 295
Meat Science 0309-1740/91/$03-50 © 1991 Elsevier Science Publishers Ltd, England. Printed in Great Britain
N. D. Cameron, M. B. Enser
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Analysis o f the genetic relationships between carcass lean weight, intramuscular f a t characteristics and eating quality traits suggest that an increase in carcass leanness will measurably change the f a t t y acid composition o f intramuscular f a t with a reduction in juiciness and, to a lesser extent, tenderness.
INTRODUCTION The fatty acid composition of the subcutaneous fat may have an effect on eating quality as myristic acid (C 14:0) and palmitic acid (C16:0) are negatively correlated with abnormal flavour' (Malmfors et al., 1978b). Muscle lipid (intramuscular fat) content may also be related to aspects of eating quality, particularly juiciness (Wood et aL, 1986), flavour (Cameron et al., 1990) and aroma (Mottram & Edwards, 1983). Therefore, the fatty acid composition of the intramuscular fat may also have an effect on eating quality. This study examined the relationships between the fatty acid composition of intramuscular fat with aspects of eating quality and the fatty acid composition of subcutaneous fat. The effect of breed, Duroc and British Landrace, on fatty acid composition of intramuscular fat was determined as breed differences in the level of intramuscular fat (Barton-Gade, 1988; Cameron et aL, 1990) and in the fatty acid composition of intramuscular fat have been reported (Bout et al., 1988). Duroc and Landrace breeds were used as they have extremely high and low levels, respectively, of intramuscular fat.
MATERIALS A N D METHODS Animals
Duroc and halothane negative British Landrace boars and gilts were performance tested on ad libitum or restricted feeding regimes, with likesexed non-littermate groups of pigs per pen. Halothane positive pigs have poor meat quality, viz. pale, soft, exudative (PSE) meat (Bejerholm, 1984) and as the Duroc is a stress-resistant breed (Webb et al., 1982), the halothane negative status of the British Landrace pigs was required, to remove confounding between breed and stress susceptibility. Pigs started test at a within-pen average weight of 30 kg and finished test at either a within-pen average weight of 80 kg for pigs fed ad libitum or after 70 days on test for restricted-fed pigs, and the food intake with restricted feeding was determined by time on test to be 0-75 g/g ad libitum daily food intake. Pigs started performance testing during an eight-week period, due to variation in
Fatty acid composition of lipid in LohgisSimus dorsi muscle of pigs
297
farrowing date. Further details of the origin of the pigs and the performance test are described in Cameron (1990a). Intramuscular fat and the inner backfat layer were analysed for fatty acid composition and aspects of meat and eating quality traits were determined on 160 pigs allocated between treatments in a 4 x 23 factorial design (four diets, two breeds, two sexes and two feeding regimes) with five pigs per subclass. The experimental design required 40 full-sib litters, with two boars and two gilts per litter, to detect breed differences of 0.9 SD for fatty acid traits.
Traits Intramuscular fat content of M. longissimust samples, taken at the last rib, were measured by extraction in a Soxhlet apparatus with diethyl ether. The fatty acid composition of intramuscular fat was determined on crosssectional slices of the M. longissimus, which were separated from adhering adipose and connective tissue. Samples were saponified and the fatty acids extracted, methylated and analysed by gas-liquid chromatography as described by Whittington et al. (1986). Fatty acid composition of lipid samples, extracted from the inner backfat layer, was determined in the same manner as for intramuscular fat. At the Institute of Food Research (Bristol), ten experienced taste panelists assessed a loin chop from each of the 160 pigs for eating quality. The loin chops, 2-3 cm thick, were grilled until the centre of the M. longissimus reached 80°C. The lean of each loin chop was trimmed of adhering adipose and connective tissue and cut into cubes of side length 2-5 cm, to assess eating quality under standardised cooking conditions. The eating quality traits measured are described by Wood et al. (1986), and the mean value of the ten taste panelists' transformed scores (Cameron et al., 1990) for each eating quality trait was used in the analysis.
Statistical analysis All traits were initially analysed using least squares analysis of variance with animals nested within litter groups. Effects were fitted for breed, feeding regime, sex and diet with two-way interactions. A final model, which consisted of litter effects and the fixed effects, breed with feeding regime and breed with sex interactions, was determined after identifying interactions which were consistently not statistically significant ( P > 0-10). Due to the similar mean slaughter weight for ad libitum (82-2kg) and restricted (79-3 kg) fed pigs and the between-pen SD (2-9 and 3-5 kg, respectively), traits were assessed at constant slaughter weight by including slaughter weight as a covariate in the model. Slaughter weight was fitted as a covariate separately t M-longissimus dorsi.
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for each feeding regime to take account of different rates of change in fatty acid traits with changes in slaughter weight. Weight of separable fat or subcutaneous fat in the carcass were considered to be breed effects and therefore, were not included in the analyses as covariates. Genetic and phenotypic parameters were estimated using an individual animal model (Quaas & Pollak, 1980) in a multivariate restricted maximum likelihood (REML) analysis (Meyer, 1985) with the final model from the least squares analysis fitted and all pedigree information incorporated in the analysis. RESULTS
Fatty acid composition of intramuscular fat Means, residual standard deviations, breed, sex and feeding regime differences for fatty acid composition of the intramuscular fat are presented in Table 1. Intramuscular fat of Duroc pigs had higher concentrations of saturated and mono-unsaturated fatty acids and lower concentrations of poly-unsaturated fatty acids than Landrace pigs and conversely for boars and gilts. Ad libitum fed pigs had higher levels of mono-unsaturated fatty acids and lower levels of poly-unsaturated fatty acids than restricted-fed pigs. For each of the individual fatty acids, the signs of the differences between the sexes were opposite to those for the differences between the feeding regimes. There was a breed with sex interaction for some fatty acids as Duroc gilts had higher concentrations of C16:1 and C18:1 and lower concentrations of C18:2 than other breed-sex combinations (Table 1). The within-breed regression coefficients of fatty acid concentration on intramuscular fat content are also given in Table 1. With increasing intramuscular fat content, concentrations of saturated, except C18:0, and mono-unsaturated fatty acids increased and concentrations of polyunsaturated fatty acids, except C18:3, decreased. The rate of change in fatty acids concentrations for Landrace pigs was essentially double that of Duroc pigs. Fatty acid composition of the inner backfat layer was examined by Cameron et al. (1990) (Table 2) and the main differences between the intramuscular fat and backfat for fatty acid composition were in C18"0, C18:1 and C18:2. Intramuscular fat of Duroc pigs contained higher concentrations of C18:0 and C18:1 than Landrace pigs but had lower concentrations in backfat, and conversely for C18:2. When compared to restricted-fed pigs, ad libitum fed pigs had lower levels of C18:2 and higher concentrations of C18:1 in intramuscular fat, but in backfat C18:2 was higher with no difference in C18:1. However, the differences between boars and gilts for fatty acid composition for intramuscular fat were similar to
387 387 184
saturated fatty acids mono-unsaturated poly-unsaturated
16-2 32.3 34.7
1.8 I 1.5 3.5 7.7 30.0 24.9 1.2 8-7 1.7 1.4
SD
21.6 20.3 - 32.2
4.1 7-7 4-2 9-8 16.0 -20.5 0.0 - 8"6 -2.1 - l'0
DurocLandrace
3.7 7.0 7.6
0.4 2.3 0"8 2.0 6-5 5.5 0.3 1.8 0.4 0.4
SED
C! 6: I 27.9 C 18:1 346.4 C18:2 146.7 mono-unsaturated 374"3 poly-unsaturated 189.6
32.0 387.0 I I 1.4 419.0 145.3
Duroc Boar Gilt 25.2 346.3 152.1 371.5 203.2
26.2 355. I 147.0 381.4 196.2
Landrace Boar Gilt 0.8 6.9 5.7 7.4 8.0
SED
Duroc and Landrace Mean Values Within Sex for Fatty Acid Composition (mg/g) of Intramuscular Fat
13 243 28 130 359 139 9 26 6 4
Cl4:0 (myristic) C16:0 (palmitic) C16:1 (palmitoleic) C18:0 (stearic) C l 8 : l (oleic) C18:2 (linoleie) C18:3 (linolenic) C20:4 (arachidonic) C22:5 (clupanodonic) C22:6
Mean
-4.7 - 27.3 25.6
-0"4 -6.2 -2.5 1.8 -24.8 20.2 1.0 3"3 0.9 0-2
Boargilt
-3.7 23.5 - 13.0
1.1 1.7 2.7 -6.4 20.6 -7.5 -0.2 - 3.7 - 1.2 -0.5
Ad-libitumrestricted
2.7 5.4 5.8
0"3 1.9 0.6 1.3 5.0 4.1 0.2 1"4 0.3 0.2
SED
0.73 3"55 - 3.30
O.10 0.71 0.24 -0.08 3.31 -2.23 0.00 -0.84 -0.12 -O.lO
Duroc
0.34 0.35 0.40
0.04 0.22 0.07 0.19 0.32 0.31 0.02 0"l I 0.02 0.02
2.32 5.73 - 6.60
0"35 1.68 0.45 0.29 5.28 -4.56 0.00 - 1.54 -0.34 -0.16
Regression coe.l~cient SE Landrace
0-49 0.99 I. 13
0.04 0.34 0.10 0.23 0.92 0.81 0.02 0.26 0.06 0.02
SE
TABLE 1 Means, SD, Breed, Sex and Feeding Regime Differences for Fatty Acid Composition (mg/g) of Intramuscular Fat and the Regression Coefficients for Intramuscular Fat Content
4
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N. D. Cameron, M. B. Enser TABLE 2 Means, SD, Breed, Sex and Feeding Regime Differences for Fatty Acid Composition (mg/g) of the Inner Backfat Layer
C18:0 C18:1 C18:2
Mean
SD
DurocLandrace
SED
Boargilt
Ad-libitumrestricted
SED
152 370 159
15"7 18-4 17-7
-5"8 -9-I 16"3
2"8 4-4 5-0
-3"8 -18"4 20"3
-7-0 0-5 8"5
2-7 3"2 3-0
Means, SD and Breed Differences for Meat and Eating Quality Traits
LDF (mg/g)a LDM (mg/g) pH
Mean
SD
DurocLandrace
SED
16.2 742 5.61
7.0 13 0.21
9.2 -7 0-01
1.1 1-6 0.03 positive value
Flavour Tenderness Juiciness
0-00 0"00 0-02
0-90 1"39 0.83
- 0"08 -0.24 0" 11
0-04 0"07 0.04
high tender juicy
a L D F = intramuscular fat content; LDM = muscle moisture content (from Cameron et aL, 1990).
the differences for the inner backfat layer. There was no evidence of a breed with sex interaction for fatty acid composition of the inner backfat layer (Table 2). The phenotypic correlations between fatty acids of intramuscular fat are given in Table 3. Saturated and mono-unsaturated fatty acids were positively associated (r = 0-59, on average), as were the poly-unsaturated fatty acids (r = 0-70, on average) and the correlations between these two groups of fatty acids were large and negative (r = -0-62, on average), excluding C18:0 and C18:3. The two fatty acids, C18:0 and C18:3, had considerably lower correlations with the other fatty acids. In general, the magnitude of the correlation coefficients between fatty acids was higher for Landrace pigs (r =0"70) than for Duroc pigs ( r = 0.57), excluding C18:0 and C18:3. The phenotypic correlations between the major fatty acids in intramuscular fat and of the inner backfat layer are also given in Table 3. The correlations which include C18:0 of the inner backfat layer are double those for the intramuscular fat and the correlation between C16:0 and C18:1 is essentially zero in the inner backfat layer, but is significantly positive in
Fatty acid composition of lipid in Longissimus dorsi muscle of pigs
301
TABLE 3 Correlations ( x 100) Between Fatty Acids of Intramuscular Fat and Between the M a j o r Fatty Acids of the Intramuscular Fat and of the Inner Backfat Layer
C16:0 C16:1 C18:0 C18:1 C18:2 C18:3 C20:4 C22:5 C22:6
C14:0
C16:0
C16:1
C18:0
C18:1
74 a 63 1 52 -55 20 -72 -62 -45
49 23 43 -64 -8 -66 -57 -43
-44 61 -54 -8 -55 -56 -36
- 15 - 14 -2 - 11 2 -6
--87 7 --86 --81 --53
Fatty acids of inner
9 82 74 52
C18:3
-23 - 17 --22
C20:4
C22:5
82 60
61
Fatty acids of Intramuscular fat Inner backfat layer
backfat layer
C16:0 C18:0 C18:1 C18:2
C18:2
C16:0
C18:0
C18:1
C18:2
C16:0
C18:0
C18:1
42 12 -8 -27
25 54 -33 - 16
16 -4 19 - 18
-35 - 15 -7 31
51 -9 -55
-42 -42
-43
a S t a n d a r d errors o f correlations are equal to 0-08.
intramuscular fat. F o r each of the major fatty acids, the correlation between the two fat tissues were positive and variable in magnitude, but correlations involving a different fatty acid from each fat depot are generally small, except for the correlations between C16:0 and C18:2. Fatty acids and eating quality The eating quality trait, acceptability, was largely a function of flavour followed, equally, by tenderness and juiciness (Cameron et al., 1990), therefore, only the correlations between fatty acid concentrations with flavour, tenderness and juiciness will be discussed. Saturated and monounsaturated fatty acids were generally positively associated with the eating quality traits, while poly-unsaturated fatty acids were negatively correlated with eating quality. However, C18:3 was positively correlated with tenderness, unlike the other poly-unsaturated fatty acids, and was essentially uncorrelated with flavour and juiciness. Correlations between fatty acids with flavour and juiciness were generally larger in magnitude than the
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c o r r e l a t i o n s i n v o l v i n g tenderness. T h e w i t h i n - b r e e d c o r r e l a t i o n s h a d a similar p a t t e r n to the p h e n o t y p i c c o r r e l a t i o n s c a l c u l a t e d f r o m d a t a o n pigs f r o m b o t h breeds, with r e g a r d to the positive c o r r e l a t i o n s o f the s a t u r a t e d a n d m o n o - u n s a t u r a t e d f a t t y acids a n d the negative c o r r e l a t i o n s o f polyu n s a t u r a t e d f a t t y acids w i t h e a t i n g quality, b u t the c o r r e l a t i o n s were larger f o r L a n d r a c e pigs t h a n f o r D u r o c pigs a n d the difference in c o r r e l a t i o n s b e t w e e n b r e e d s was n o t statistically significant.
Fatty acids and meat quality T h e a s s o c i a t i o n b e t w e e n f a t t y acids a n d fat c o n t e n t o f the M . longissimus were o f the s a m e o r d e r o f m a g n i t u d e for b o t h breeds, as s a t u r a t e d a n d m o n o - u n s a t u r a t e d f a t t y acids were positively associated, while polyu n s a t u r a t e d f a t t y acids were n e g a t i v e l y associated, e x c e p t C 1 8 : 0 a n d C 1 8 : 3 ( T a b l e 4). H o w e v e r , the c o r r e l a t i o n s b e t w e e n f a t t y acids with muscle m o i s t u r e c o n t e n t a n d m u s c l e p H were b r e e d - d e p e n d e n t . In D u r o c pigs, the r e l a t i o n s h i p b e t w e e n f a t t y acids a n d M . longissimus m o i s t u r e c o n t e n t was o p p o s i t e to t h a t w i t h i n t r a m u s c u l a r fat, b u t in L a n d r a c e pigs the f a t t y acids were essentially i n d e p e n d e n t o f m u s c l e m o i s t u r e c o n t e n t . In c o n t r a s t , TABLE 4 Correlations between Fatty Acids of the Intramuscular Fat with Eating Quality and Within Breed Correlations Between Fatty Acid Concentrations with Meat Quality Traits C14:0 C16:0
Flav° Tend Juicy Accep
C16:1
C18:0 C18:1 C18:2 C18:3
C20:4
C22:5 C22:6
14 15 11 19
13 5 8 12
17 8 21 17
-4 4 6 1
19 9 19 19
-21 -6 - 19 -20
5 23 10 15
--20 -20 - 19 -26
-23 -21 -23 -28
- 17 - 16 -21 -21
Landrace LDF 67 LDM -8 pH 32
47 -1 25
44 6 34
9 1 - 10
54 2 31
-53 1 -26
3 -5 26
-55 -1 -34
-53 -3 -29
--30 -17 -41
37 -23 -- 10
40 --26 - 14
-5 13 12
80 --52 2
-66 38 -8
4 -1 11
-69 46 4
-56 38 11
-54 40 --8
Duroc LDF LDM pH
32 --30 -3
° Abbreviations are Flavour, Tenderness, Juiciness and Acceptability. LDF = intramuscular fat content. LDM = muscle moisture content. pH ~- muscle pH. Standard errors of correlations are equal to 0-08 for both breeds combined and 0-11 within breed.
Fatty acid composition of lipid in Longissimus dorsi muscle of pigs
303
correlations between fatty acids and muscle pH for Landrace pigs were of the same size as those between fatty acids and intramuscular fat, except that there was also a positive correlation between C18:3 and muscle pH, while for Duroc pigs the correlations were small.
Genetic parameters The heritability estimates for the fatty acids of the intramuscular fat were between 0,25 and 0-5, except for C18:0 and C18:3 with values of 0-73 and 0-62, respectively (Table 5). The genetic and phenotypic correlations between fatty acids and lean weight are such that the intramuscular fat becomes more unsaturated as carcass lean weight increases. The genetic correlations between the major fatty acids, C 16: 0, C 18:0, C18:1 and C 18: 2, with carcass lean weight (Table 5) were similar to the correlations between the fatty acids TABLE 5 Genetic P a r a m e t e r s ( x 100) for Muscle and F a t Characteristics, Eating Quality Traits and Carcass Lean Weight
Trait
Phenotypic correlation a
Heritability (h 2)
Genetic correlation (rG)*
Relative response b
C14:0 C16:0 C16:1 C18:0 C18:1 C18:2 C18:3 C20:4 C22 : 5 C22:6
-23 c -33 - 10 -11 - 24 32 1 30 24 12
33 d 24 50 73 28 24 62 24 41 42
-23 e -28 4 -25 -20 46 -17 33 24 9
- 15 - 16 3 -25 - 12 26 -15 19 18 7
I n t r a m u s c u l a r fat Muscle m o i s t u r e Muscle p H
- 25 12 -- 7
53 26 20
- 41 47 -- 50
- 34 28 -- 26
Flavour Tenderness Juiciness
-- 15 - 11 3
16
-- 16
23
-29
- 16
18
- 47
- 24
-- 7
° P h e n o t y p i c a n d genetic correlations between trait a n d carcass lean weight. b R e s p o n s e in trait relative to response in carcass lean weight (phenotypic s t a n d a r d deviation units) with selection for increased carcass lean weight (relative response = rGhtralulhlean), where the heritability o f carcass lean weight is 0-75. c Average s t a n d a r d e r r o r o f p h e n o t y p i c correlation estimates = 0.08. d A v e r a g e s t a n d a r d e r r o r o f heritability estimates = 0.17. e A v e r a g e s t a n d a r d e r r o r o f genetic correlation estimates = 0.23.
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N. D. Cameron, M. B. Enser
of the inner layer of subcutaneous fat and carcass lean weight (-0"38, -0-30, -0-22 and 0-47, respectively) as were the phenotypic correlations (-0"33, -0-16, -0-09 and 0-32) (Cameron, 1990b).
DISCUSSION The lipid content of the M . longissimus was a major factor which influenced fatty acid composition of intramuscular fat for both breeds and was significantly related to muscle pH in Landrace pigs and to moisture content in Duroc pigs. With increased muscle fat content, the fat contained more saturated, C 14:0 and C 16:0, and mono-unsaturated fatty acids, C 16:1 and C18:1, and less poly-unsaturated fatty acids, C18:2, C20:4, C22:5 and C22:6, and similar results have been reported for the Landrace and Yorkshire breeds (Malmfors et al., 1978a). The high degree of association between the fatty acids suggested that as intramuscular fat content increased, there was a rapid dilution of poly-unsaturated fatty acids by saturated and mono-unsaturated fatty acids, particularly in Landrace pigs. The dilution of poly-unsaturated fatty acids by saturated and monounsaturated fatty acids is due to the difference in fatty acid composition between the muscle phospholipids and the neutral lipids. The muscle content of phospholipids is relatively constant (5 mg/g wet tissue) and contains mainly poly-unsaturated fatty acids, while the neutral lipids in the muscle, which mainly consist of saturated and mono-unsaturated fatty acids, increase as the intramuscular fat content increases (Hornstein et al., 1961; Allen et al., 1967; Luddy e t al., 1970; Wood & Lister, 1973; Sharma et aL, 1987). An asymptotic relationship between intramuscular fat content and the degree of saturation of the fat (Lawrie et al., 1963) may account for the different rates of change between the two breeds in fatty acid composition of the fat, due to the higher intramuscular fat content of the Duroc compared to the Landrace (20"8 versus 11-6 mg/g, Cameron et al., 1990). In Landrace pigs, muscle pH and fat content were positively associated, presumably through the respective positive and negative correlations of muscle pH with mono- and poly-unsaturated fatty acids. Therefore, the leaner Landrace pigs will have a faster muscle pH fall, which may indicate some PSE sensitivity in these Landrace pigs due to incomplete penetrance of the halothane gene (Smith & Bampton, 1977; Southwood et aL, 1988), even though the pigs were classed as halothane negative by halothane testing. In Duroc pigs, muscle moisture content decreased as intramuscular fat increased (r = --0"65) and the correlations between fatty acids and muscle moisture content were opposite in sign to those with intramuscular fat, but were lower in magnitude. The lack of similar correlations between muscle
Fatty acid composition of lipid in Longissimus dorsi muscle of pigs
305
moisture content with intramuscular fat content and fatty acids in Landrace pigs (r = --0"36) was due to lower covariances of the latter traits, rather than to differences in the variation of muscle moisture content for Landrace (79.0 mg/g 2) and Duroc (89.6 mg/g 2) pigs. There were breed-sex differences for fatty acids C18:1 and C18:2 and the eating quality traits as Duroc gilts had higher levels of C18:1 but lower levels of C18:2, and Duroc boars had poorer flavour and tenderness than other breed-sex combinations, although Duroc pigs were tougher and juicier than Landrace pigs (Cameron et aL, 1990). Differences in intramuscular fat content in the various breed-sex classes accounted for approximately half of the differences in C18:1, C18:2 and tenderness. The differences between the breed-sex classes were not substantially reduced for flavour and juiciness at constant intramuscular fat content, but there was more of a reduction in Landrace pigs than there was in Duroc pigs. The poorer flavour of Duroc boars was, therefore, not due to differences in intramuscular fat content and is unlikely to be a function of the particular fatty acid composition of the intramuscular fat, as the overall fatty acid composition of Duroc boars was similar to that of Landrace gilts (Table 1). The higher concentration of 5~androst-16-en-3-one in Durocs compared with white breeds (Wood et al., 1988) may be the most likely cause of the poorer flavour score of Duroc boars. High androstenone levels have been associated with certain fatty acid compositions, but this relationship may be breed-specific (Malmfors et aL, 1978b). The similar negative relationships between all the polyunsaturated fatty acids, except C18:3, with flavour contrasts with other reports that changes in the concentration of C18:2 and C20:4, which is derived from C18:2, have little effect on flavour (Wahlstrom et al., 1971; H a r t m a n et aL, 1985). The low correlations between C18:3 with intramuscular fat content and flavour differs from other studies. Malmfors et al. (1978a) reported positive correlations between C18:3 and intramuscular fat content in Landrace and Yorkshire pigs. High concentrations of C 18:3 and possibly other n-3 fatty acids derived from C 18:3, have been associated with less desirable flavours in beef (Melton et al., 1982; Miller et aL, 1987). The absence of an effect on flavour of C18:3 in pigs may result from differences in the relative concentrations of C 18:2 and C 18:3 between the species. However, the tenderness of meat from Duroc pigs was largely due to a higher intramuscular fat content than for Landrace pigs. The main selection objective in pig breeding is efficient lean meat production but selection for leaner meat has been associated with reduced meat quality (Kempster et al., 1986) and reduced eating quality, but the latter was not substantiated in the study of Wood et al. (1986). An examination of the genetic parameters involving carcass lean, muscle and fat characteristics and eating quality traits (Table 5) will enable some quantification of the
306
N. D. Cameron, l~. B. Enser
correlated responses in these traits to selection for improved carcass lean. In terms of phenotypic standard deviations, the magnitude of the proportional responses in muscle and fat characteristics and in eating quality traits relative to the response in carcass lean were approximately 0.29 for muscle fat and moisture content and muscle pH, and 0-16 on average for intramuscular fatty acids. The actual responses to selection for reduced backfat thickness (Wood et al., 1978) were higher C18:2 and lower C18:1 with increased drip loss, which were qualitatively consistent with the predicted responses. The relative responses were also in agreement with the results of Kempster et al. (1986) and W o o d et al. (1986), that there would be a measureable response in muscle and fat characteristics given selection to improve carcass leanness. The relative responses for eating quality traits were -0-07, --0.16 and - 0 - 2 4 for flavour, tenderness and juiciness, which were proportionally consistent with the study of Kempster et aL, (1986) where the differences between loin chops of lean and fat pigs were - 0 . 1 0 , - 0 . 2 0 and - 0 , 2 6 for flavour, tenderness and juiciness, respectively. W o o d et al. (1986) reported that the only statistically significant difference between lean and fat pigs was that juiciness was lower in lean pigs. The results from the current study suggest that the correlated responses in eating quality traits to selection for increased carcass leanness will primarily be a reduction in juiciness and, to a lesser extent, tenderness.
ACKNOWLEDGEMENTS The Meat and Livestock Commission and Dalgety Agriculture Ltd provided some of the funding for the experiment.
REFERENCES Allen, E., Bray, R. W. & Cassens, R. G. (1967). J. Food Sci., 32, 26. Barton-Gade, P. A. (1988). Proc. 34th Int. Congr. Meat Sci. Technol., Brisbane, Australia, p. 568. Berjerholm, C. (1984). Proc. 30th Europ. Meet. Meat Res. Workers, p. 196. Bout, J., Girand, J. P., Sellier, P., Runavot, J. P. & Salort, D. (1988). 20es Journbes de la Recherche Porcine en France, p. 279. Cameron, N. D. (1990a). Anim. Prod., 50, 141. Cameron, N. D. (1990b). Livestock Prod. Sci., 26, 119. Cameron, N. D., Warriss, P. D., Porter, S. J. & Enser, M. (1990). Meat Sci., 27, 227. Hartman, A. D., Costello, W. J., Libal, G. W. & Wahlstrom, R. C. (1985). J. Anim. Sci., 60, 212. Hornstein, I., Crowe, P. F. & Heimberg, M. J. (1961). J. Food Sci., 26, 581.
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Kempster, A. J., Dilworth, A. W., Evans, D. G. & Fisher, K. D. (1986). Anim. Prod., 43, 517. Lawrie, R. A., Pomeroy, R. W. & Cuthbertson, A. (1963). J. Agric. Sci., 60, 195. Luddy, F. E., Herb, S. F., Magidman, P., Spinelli, A. M. & Wasserman, A. E. (1970). J. Am. Oil Chem. Soc., 47, 65. Malmfors, B., Lundstrom, K. & Hansson, I. (1978a). Swed. J. Agric. Res., 8, 161. Malmfors, B., Lundstrom, K. & Hansson, I. (1978b). Swed. J. Agric. Res., 8, 25. Melton, S. L., Black, J. M., Davis, G. W. & Backus, W. R. (1982). J. FoodSci., 47, 699. Meyer, K. (1985). Biometrics, 41, 153. Miller, G. J., Field, R, A., Medieros, L. & Nelms, G. E. (1987). J. FoodSci., 52, 526. Mottram, D. S. & Edwards, R. A. (1983). J. Sci. Food Agric., 34, 517. Quaas, R. L. & Pollak, E. J. (1980). J. Anim. Sci., 51, 1277. Sharma, N., Gandemer, G. & Goutefongea, R. (1987). Meat Sci., 19, 121. Smith, C. & Bampton, P. R. (1977). Genetical Res., Camb., 29, 287. Southwood, O. I., Simpson, S. P., Curran, M. K. & Webb, A. J. (1988). Anim. Prod., 46, 97. Wahlstrom, R. C., Libal, G. W. & Berns, R. J. (1971). J. Anim. Sci., 32, 891. Webb, A. J., Carden, A. E., Smith, C. & Imlah, P. (1982). Proc. 2nd Worm Congr. on Genetics Applied to Livestock Production, Madrid, 5, p. 588. Whittington, F. M., Prescott, N. J., Wood, J. D. & Enser, M. (1986). J. Sci. Food Agric., 37, 753. Wood, J. D. & Lister, D. (1973). 3". Sci. Food Agric., 24, 1449. Wood, J. D., Enser, M. B., MacFie, H. J. H., Smith, W. C., Chadwick, J. P., Ellis, M. & Laird, R. (1978). Meat Sci., 2, 289. Wood, J. D., Jones, R. C. D., Francombe, M. A. & Whelehan, O. P. (1986). Anim. Prod., 43, 535. Wood, J. D., Edwards, S. A. & Bichard, M. (1988). Proc. 34th lnt. Congr. Meat Sci. Technol., Brisbane, Australia, p. 571.
Fatty Acid Composition of Lipid in Longissimus Dorsi Muscle of Duroc and British Landrace Pigs and its Relationship with Eating Quality
N. D. Cameron AFRC Institute of Animal Physiology and Genetics Research, Edinburgh Research Station, Roslin, Midlothian, EH25 9PS, Scotland
& M. B. Enser AFRC Institute of Food Research, Bristol Laboratory, Langford, Bristol, BSI8 7DY, England (Received 3 May 1990; revised version received 10 June 1990; accepted 18 June 1990)
ABSTRACT The fatty acid composition of intramuscular fat from Duroc and halothane negative British Landrace pigs was determined and the relationships between fatty acid concentrations and aspects of eating quality were estimated from data on 160 pigs. Boars and gilts from each breed were performance tested on ad libitum or restricted feeding regimes with an average slaughter weight of 80 kg. Eating quality was assessed by ten experienced taste panelists. Intramuscular fat of Duroc pigs had higher concentrations of saturated and mono-unsaturated fatty acids and lower concentrations of poly-unsaturated fatty acids than Landrace pigs. With increasing intramuscular fat content, concentrations of saturated and mono-unsaturated fatty acids increased and concentrations of poly-unsaturated fatty acids decreased and the rate of change in fatty acid concentrations was greater in Landrace pigs than in Duroc pigs. Eating quality traits were generally improved as the concentration of mono-unsaturated fatty acids increased and poly-unsaturated fatty acids decreased. 295
Meat Science 0309-1740/91/$03-50 © 1991 Elsevier Science Publishers Ltd, England. Printed in Great Britain
N. D. Cameron, M. B. Enser
296
Analysis o f the genetic relationships between carcass lean weight, intramuscular f a t characteristics and eating quality traits suggest that an increase in carcass leanness will measurably change the f a t t y acid composition o f intramuscular f a t with a reduction in juiciness and, to a lesser extent, tenderness.
INTRODUCTION The fatty acid composition of the subcutaneous fat may have an effect on eating quality as myristic acid (C 14:0) and palmitic acid (C16:0) are negatively correlated with abnormal flavour' (Malmfors et al., 1978b). Muscle lipid (intramuscular fat) content may also be related to aspects of eating quality, particularly juiciness (Wood et aL, 1986), flavour (Cameron et al., 1990) and aroma (Mottram & Edwards, 1983). Therefore, the fatty acid composition of the intramuscular fat may also have an effect on eating quality. This study examined the relationships between the fatty acid composition of intramuscular fat with aspects of eating quality and the fatty acid composition of subcutaneous fat. The effect of breed, Duroc and British Landrace, on fatty acid composition of intramuscular fat was determined as breed differences in the level of intramuscular fat (Barton-Gade, 1988; Cameron et aL, 1990) and in the fatty acid composition of intramuscular fat have been reported (Bout et al., 1988). Duroc and Landrace breeds were used as they have extremely high and low levels, respectively, of intramuscular fat.
MATERIALS A N D METHODS Animals
Duroc and halothane negative British Landrace boars and gilts were performance tested on ad libitum or restricted feeding regimes, with likesexed non-littermate groups of pigs per pen. Halothane positive pigs have poor meat quality, viz. pale, soft, exudative (PSE) meat (Bejerholm, 1984) and as the Duroc is a stress-resistant breed (Webb et al., 1982), the halothane negative status of the British Landrace pigs was required, to remove confounding between breed and stress susceptibility. Pigs started test at a within-pen average weight of 30 kg and finished test at either a within-pen average weight of 80 kg for pigs fed ad libitum or after 70 days on test for restricted-fed pigs, and the food intake with restricted feeding was determined by time on test to be 0-75 g/g ad libitum daily food intake. Pigs started performance testing during an eight-week period, due to variation in
Fatty acid composition of lipid in LohgisSimus dorsi muscle of pigs
297
farrowing date. Further details of the origin of the pigs and the performance test are described in Cameron (1990a). Intramuscular fat and the inner backfat layer were analysed for fatty acid composition and aspects of meat and eating quality traits were determined on 160 pigs allocated between treatments in a 4 x 23 factorial design (four diets, two breeds, two sexes and two feeding regimes) with five pigs per subclass. The experimental design required 40 full-sib litters, with two boars and two gilts per litter, to detect breed differences of 0.9 SD for fatty acid traits.
Traits Intramuscular fat content of M. longissimust samples, taken at the last rib, were measured by extraction in a Soxhlet apparatus with diethyl ether. The fatty acid composition of intramuscular fat was determined on crosssectional slices of the M. longissimus, which were separated from adhering adipose and connective tissue. Samples were saponified and the fatty acids extracted, methylated and analysed by gas-liquid chromatography as described by Whittington et al. (1986). Fatty acid composition of lipid samples, extracted from the inner backfat layer, was determined in the same manner as for intramuscular fat. At the Institute of Food Research (Bristol), ten experienced taste panelists assessed a loin chop from each of the 160 pigs for eating quality. The loin chops, 2-3 cm thick, were grilled until the centre of the M. longissimus reached 80°C. The lean of each loin chop was trimmed of adhering adipose and connective tissue and cut into cubes of side length 2-5 cm, to assess eating quality under standardised cooking conditions. The eating quality traits measured are described by Wood et al. (1986), and the mean value of the ten taste panelists' transformed scores (Cameron et al., 1990) for each eating quality trait was used in the analysis.
Statistical analysis All traits were initially analysed using least squares analysis of variance with animals nested within litter groups. Effects were fitted for breed, feeding regime, sex and diet with two-way interactions. A final model, which consisted of litter effects and the fixed effects, breed with feeding regime and breed with sex interactions, was determined after identifying interactions which were consistently not statistically significant ( P > 0-10). Due to the similar mean slaughter weight for ad libitum (82-2kg) and restricted (79-3 kg) fed pigs and the between-pen SD (2-9 and 3-5 kg, respectively), traits were assessed at constant slaughter weight by including slaughter weight as a covariate in the model. Slaughter weight was fitted as a covariate separately t M-longissimus dorsi.
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N. D. Cameron, M. B. Enser
for each feeding regime to take account of different rates of change in fatty acid traits with changes in slaughter weight. Weight of separable fat or subcutaneous fat in the carcass were considered to be breed effects and therefore, were not included in the analyses as covariates. Genetic and phenotypic parameters were estimated using an individual animal model (Quaas & Pollak, 1980) in a multivariate restricted maximum likelihood (REML) analysis (Meyer, 1985) with the final model from the least squares analysis fitted and all pedigree information incorporated in the analysis. RESULTS
Fatty acid composition of intramuscular fat Means, residual standard deviations, breed, sex and feeding regime differences for fatty acid composition of the intramuscular fat are presented in Table 1. Intramuscular fat of Duroc pigs had higher concentrations of saturated and mono-unsaturated fatty acids and lower concentrations of poly-unsaturated fatty acids than Landrace pigs and conversely for boars and gilts. Ad libitum fed pigs had higher levels of mono-unsaturated fatty acids and lower levels of poly-unsaturated fatty acids than restricted-fed pigs. For each of the individual fatty acids, the signs of the differences between the sexes were opposite to those for the differences between the feeding regimes. There was a breed with sex interaction for some fatty acids as Duroc gilts had higher concentrations of C16:1 and C18:1 and lower concentrations of C18:2 than other breed-sex combinations (Table 1). The within-breed regression coefficients of fatty acid concentration on intramuscular fat content are also given in Table 1. With increasing intramuscular fat content, concentrations of saturated, except C18:0, and mono-unsaturated fatty acids increased and concentrations of polyunsaturated fatty acids, except C18:3, decreased. The rate of change in fatty acids concentrations for Landrace pigs was essentially double that of Duroc pigs. Fatty acid composition of the inner backfat layer was examined by Cameron et al. (1990) (Table 2) and the main differences between the intramuscular fat and backfat for fatty acid composition were in C18"0, C18:1 and C18:2. Intramuscular fat of Duroc pigs contained higher concentrations of C18:0 and C18:1 than Landrace pigs but had lower concentrations in backfat, and conversely for C18:2. When compared to restricted-fed pigs, ad libitum fed pigs had lower levels of C18:2 and higher concentrations of C18:1 in intramuscular fat, but in backfat C18:2 was higher with no difference in C18:1. However, the differences between boars and gilts for fatty acid composition for intramuscular fat were similar to
387 387 184
saturated fatty acids mono-unsaturated poly-unsaturated
16-2 32.3 34.7
1.8 I 1.5 3.5 7.7 30.0 24.9 1.2 8-7 1.7 1.4
SD
21.6 20.3 - 32.2
4.1 7-7 4-2 9-8 16.0 -20.5 0.0 - 8"6 -2.1 - l'0
DurocLandrace
3.7 7.0 7.6
0.4 2.3 0"8 2.0 6-5 5.5 0.3 1.8 0.4 0.4
SED
C! 6: I 27.9 C 18:1 346.4 C18:2 146.7 mono-unsaturated 374"3 poly-unsaturated 189.6
32.0 387.0 I I 1.4 419.0 145.3
Duroc Boar Gilt 25.2 346.3 152.1 371.5 203.2
26.2 355. I 147.0 381.4 196.2
Landrace Boar Gilt 0.8 6.9 5.7 7.4 8.0
SED
Duroc and Landrace Mean Values Within Sex for Fatty Acid Composition (mg/g) of Intramuscular Fat
13 243 28 130 359 139 9 26 6 4
Cl4:0 (myristic) C16:0 (palmitic) C16:1 (palmitoleic) C18:0 (stearic) C l 8 : l (oleic) C18:2 (linoleie) C18:3 (linolenic) C20:4 (arachidonic) C22:5 (clupanodonic) C22:6
Mean
-4.7 - 27.3 25.6
-0"4 -6.2 -2.5 1.8 -24.8 20.2 1.0 3"3 0.9 0-2
Boargilt
-3.7 23.5 - 13.0
1.1 1.7 2.7 -6.4 20.6 -7.5 -0.2 - 3.7 - 1.2 -0.5
Ad-libitumrestricted
2.7 5.4 5.8
0"3 1.9 0.6 1.3 5.0 4.1 0.2 1"4 0.3 0.2
SED
0.73 3"55 - 3.30
O.10 0.71 0.24 -0.08 3.31 -2.23 0.00 -0.84 -0.12 -O.lO
Duroc
0.34 0.35 0.40
0.04 0.22 0.07 0.19 0.32 0.31 0.02 0"l I 0.02 0.02
2.32 5.73 - 6.60
0"35 1.68 0.45 0.29 5.28 -4.56 0.00 - 1.54 -0.34 -0.16
Regression coe.l~cient SE Landrace
0-49 0.99 I. 13
0.04 0.34 0.10 0.23 0.92 0.81 0.02 0.26 0.06 0.02
SE
TABLE 1 Means, SD, Breed, Sex and Feeding Regime Differences for Fatty Acid Composition (mg/g) of Intramuscular Fat and the Regression Coefficients for Intramuscular Fat Content
4
Q
o ~.: ~
E~ ~'
~. E"
~
300
N. D. Cameron, M. B. Enser TABLE 2 Means, SD, Breed, Sex and Feeding Regime Differences for Fatty Acid Composition (mg/g) of the Inner Backfat Layer
C18:0 C18:1 C18:2
Mean
SD
DurocLandrace
SED
Boargilt
Ad-libitumrestricted
SED
152 370 159
15"7 18-4 17-7
-5"8 -9-I 16"3
2"8 4-4 5-0
-3"8 -18"4 20"3
-7-0 0-5 8"5
2-7 3"2 3-0
Means, SD and Breed Differences for Meat and Eating Quality Traits
LDF (mg/g)a LDM (mg/g) pH
Mean
SD
DurocLandrace
SED
16.2 742 5.61
7.0 13 0.21
9.2 -7 0-01
1.1 1-6 0.03 positive value
Flavour Tenderness Juiciness
0-00 0"00 0-02
0-90 1"39 0.83
- 0"08 -0.24 0" 11
0-04 0"07 0.04
high tender juicy
a L D F = intramuscular fat content; LDM = muscle moisture content (from Cameron et aL, 1990).
the differences for the inner backfat layer. There was no evidence of a breed with sex interaction for fatty acid composition of the inner backfat layer (Table 2). The phenotypic correlations between fatty acids of intramuscular fat are given in Table 3. Saturated and mono-unsaturated fatty acids were positively associated (r = 0-59, on average), as were the poly-unsaturated fatty acids (r = 0-70, on average) and the correlations between these two groups of fatty acids were large and negative (r = -0-62, on average), excluding C18:0 and C18:3. The two fatty acids, C18:0 and C18:3, had considerably lower correlations with the other fatty acids. In general, the magnitude of the correlation coefficients between fatty acids was higher for Landrace pigs (r =0"70) than for Duroc pigs ( r = 0.57), excluding C18:0 and C18:3. The phenotypic correlations between the major fatty acids in intramuscular fat and of the inner backfat layer are also given in Table 3. The correlations which include C18:0 of the inner backfat layer are double those for the intramuscular fat and the correlation between C16:0 and C18:1 is essentially zero in the inner backfat layer, but is significantly positive in
Fatty acid composition of lipid in Longissimus dorsi muscle of pigs
301
TABLE 3 Correlations ( x 100) Between Fatty Acids of Intramuscular Fat and Between the M a j o r Fatty Acids of the Intramuscular Fat and of the Inner Backfat Layer
C16:0 C16:1 C18:0 C18:1 C18:2 C18:3 C20:4 C22:5 C22:6
C14:0
C16:0
C16:1
C18:0
C18:1
74 a 63 1 52 -55 20 -72 -62 -45
49 23 43 -64 -8 -66 -57 -43
-44 61 -54 -8 -55 -56 -36
- 15 - 14 -2 - 11 2 -6
--87 7 --86 --81 --53
Fatty acids of inner
9 82 74 52
C18:3
-23 - 17 --22
C20:4
C22:5
82 60
61
Fatty acids of Intramuscular fat Inner backfat layer
backfat layer
C16:0 C18:0 C18:1 C18:2
C18:2
C16:0
C18:0
C18:1
C18:2
C16:0
C18:0
C18:1
42 12 -8 -27
25 54 -33 - 16
16 -4 19 - 18
-35 - 15 -7 31
51 -9 -55
-42 -42
-43
a S t a n d a r d errors o f correlations are equal to 0-08.
intramuscular fat. F o r each of the major fatty acids, the correlation between the two fat tissues were positive and variable in magnitude, but correlations involving a different fatty acid from each fat depot are generally small, except for the correlations between C16:0 and C18:2. Fatty acids and eating quality The eating quality trait, acceptability, was largely a function of flavour followed, equally, by tenderness and juiciness (Cameron et al., 1990), therefore, only the correlations between fatty acid concentrations with flavour, tenderness and juiciness will be discussed. Saturated and monounsaturated fatty acids were generally positively associated with the eating quality traits, while poly-unsaturated fatty acids were negatively correlated with eating quality. However, C18:3 was positively correlated with tenderness, unlike the other poly-unsaturated fatty acids, and was essentially uncorrelated with flavour and juiciness. Correlations between fatty acids with flavour and juiciness were generally larger in magnitude than the
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N. D. Cameron, M. B. Enser
c o r r e l a t i o n s i n v o l v i n g tenderness. T h e w i t h i n - b r e e d c o r r e l a t i o n s h a d a similar p a t t e r n to the p h e n o t y p i c c o r r e l a t i o n s c a l c u l a t e d f r o m d a t a o n pigs f r o m b o t h breeds, with r e g a r d to the positive c o r r e l a t i o n s o f the s a t u r a t e d a n d m o n o - u n s a t u r a t e d f a t t y acids a n d the negative c o r r e l a t i o n s o f polyu n s a t u r a t e d f a t t y acids w i t h e a t i n g quality, b u t the c o r r e l a t i o n s were larger f o r L a n d r a c e pigs t h a n f o r D u r o c pigs a n d the difference in c o r r e l a t i o n s b e t w e e n b r e e d s was n o t statistically significant.
Fatty acids and meat quality T h e a s s o c i a t i o n b e t w e e n f a t t y acids a n d fat c o n t e n t o f the M . longissimus were o f the s a m e o r d e r o f m a g n i t u d e for b o t h breeds, as s a t u r a t e d a n d m o n o - u n s a t u r a t e d f a t t y acids were positively associated, while polyu n s a t u r a t e d f a t t y acids were n e g a t i v e l y associated, e x c e p t C 1 8 : 0 a n d C 1 8 : 3 ( T a b l e 4). H o w e v e r , the c o r r e l a t i o n s b e t w e e n f a t t y acids with muscle m o i s t u r e c o n t e n t a n d m u s c l e p H were b r e e d - d e p e n d e n t . In D u r o c pigs, the r e l a t i o n s h i p b e t w e e n f a t t y acids a n d M . longissimus m o i s t u r e c o n t e n t was o p p o s i t e to t h a t w i t h i n t r a m u s c u l a r fat, b u t in L a n d r a c e pigs the f a t t y acids were essentially i n d e p e n d e n t o f m u s c l e m o i s t u r e c o n t e n t . In c o n t r a s t , TABLE 4 Correlations between Fatty Acids of the Intramuscular Fat with Eating Quality and Within Breed Correlations Between Fatty Acid Concentrations with Meat Quality Traits C14:0 C16:0
Flav° Tend Juicy Accep
C16:1
C18:0 C18:1 C18:2 C18:3
C20:4
C22:5 C22:6
14 15 11 19
13 5 8 12
17 8 21 17
-4 4 6 1
19 9 19 19
-21 -6 - 19 -20
5 23 10 15
--20 -20 - 19 -26
-23 -21 -23 -28
- 17 - 16 -21 -21
Landrace LDF 67 LDM -8 pH 32
47 -1 25
44 6 34
9 1 - 10
54 2 31
-53 1 -26
3 -5 26
-55 -1 -34
-53 -3 -29
--30 -17 -41
37 -23 -- 10
40 --26 - 14
-5 13 12
80 --52 2
-66 38 -8
4 -1 11
-69 46 4
-56 38 11
-54 40 --8
Duroc LDF LDM pH
32 --30 -3
° Abbreviations are Flavour, Tenderness, Juiciness and Acceptability. LDF = intramuscular fat content. LDM = muscle moisture content. pH ~- muscle pH. Standard errors of correlations are equal to 0-08 for both breeds combined and 0-11 within breed.
Fatty acid composition of lipid in Longissimus dorsi muscle of pigs
303
correlations between fatty acids and muscle pH for Landrace pigs were of the same size as those between fatty acids and intramuscular fat, except that there was also a positive correlation between C18:3 and muscle pH, while for Duroc pigs the correlations were small.
Genetic parameters The heritability estimates for the fatty acids of the intramuscular fat were between 0,25 and 0-5, except for C18:0 and C18:3 with values of 0-73 and 0-62, respectively (Table 5). The genetic and phenotypic correlations between fatty acids and lean weight are such that the intramuscular fat becomes more unsaturated as carcass lean weight increases. The genetic correlations between the major fatty acids, C 16: 0, C 18:0, C18:1 and C 18: 2, with carcass lean weight (Table 5) were similar to the correlations between the fatty acids TABLE 5 Genetic P a r a m e t e r s ( x 100) for Muscle and F a t Characteristics, Eating Quality Traits and Carcass Lean Weight
Trait
Phenotypic correlation a
Heritability (h 2)
Genetic correlation (rG)*
Relative response b
C14:0 C16:0 C16:1 C18:0 C18:1 C18:2 C18:3 C20:4 C22 : 5 C22:6
-23 c -33 - 10 -11 - 24 32 1 30 24 12
33 d 24 50 73 28 24 62 24 41 42
-23 e -28 4 -25 -20 46 -17 33 24 9
- 15 - 16 3 -25 - 12 26 -15 19 18 7
I n t r a m u s c u l a r fat Muscle m o i s t u r e Muscle p H
- 25 12 -- 7
53 26 20
- 41 47 -- 50
- 34 28 -- 26
Flavour Tenderness Juiciness
-- 15 - 11 3
16
-- 16
23
-29
- 16
18
- 47
- 24
-- 7
° P h e n o t y p i c a n d genetic correlations between trait a n d carcass lean weight. b R e s p o n s e in trait relative to response in carcass lean weight (phenotypic s t a n d a r d deviation units) with selection for increased carcass lean weight (relative response = rGhtralulhlean), where the heritability o f carcass lean weight is 0-75. c Average s t a n d a r d e r r o r o f p h e n o t y p i c correlation estimates = 0.08. d A v e r a g e s t a n d a r d e r r o r o f heritability estimates = 0.17. e A v e r a g e s t a n d a r d e r r o r o f genetic correlation estimates = 0.23.
304
N. D. Cameron, M. B. Enser
of the inner layer of subcutaneous fat and carcass lean weight (-0"38, -0-30, -0-22 and 0-47, respectively) as were the phenotypic correlations (-0"33, -0-16, -0-09 and 0-32) (Cameron, 1990b).
DISCUSSION The lipid content of the M . longissimus was a major factor which influenced fatty acid composition of intramuscular fat for both breeds and was significantly related to muscle pH in Landrace pigs and to moisture content in Duroc pigs. With increased muscle fat content, the fat contained more saturated, C 14:0 and C 16:0, and mono-unsaturated fatty acids, C 16:1 and C18:1, and less poly-unsaturated fatty acids, C18:2, C20:4, C22:5 and C22:6, and similar results have been reported for the Landrace and Yorkshire breeds (Malmfors et al., 1978a). The high degree of association between the fatty acids suggested that as intramuscular fat content increased, there was a rapid dilution of poly-unsaturated fatty acids by saturated and mono-unsaturated fatty acids, particularly in Landrace pigs. The dilution of poly-unsaturated fatty acids by saturated and monounsaturated fatty acids is due to the difference in fatty acid composition between the muscle phospholipids and the neutral lipids. The muscle content of phospholipids is relatively constant (5 mg/g wet tissue) and contains mainly poly-unsaturated fatty acids, while the neutral lipids in the muscle, which mainly consist of saturated and mono-unsaturated fatty acids, increase as the intramuscular fat content increases (Hornstein et al., 1961; Allen et al., 1967; Luddy e t al., 1970; Wood & Lister, 1973; Sharma et aL, 1987). An asymptotic relationship between intramuscular fat content and the degree of saturation of the fat (Lawrie et al., 1963) may account for the different rates of change between the two breeds in fatty acid composition of the fat, due to the higher intramuscular fat content of the Duroc compared to the Landrace (20"8 versus 11-6 mg/g, Cameron et al., 1990). In Landrace pigs, muscle pH and fat content were positively associated, presumably through the respective positive and negative correlations of muscle pH with mono- and poly-unsaturated fatty acids. Therefore, the leaner Landrace pigs will have a faster muscle pH fall, which may indicate some PSE sensitivity in these Landrace pigs due to incomplete penetrance of the halothane gene (Smith & Bampton, 1977; Southwood et aL, 1988), even though the pigs were classed as halothane negative by halothane testing. In Duroc pigs, muscle moisture content decreased as intramuscular fat increased (r = --0"65) and the correlations between fatty acids and muscle moisture content were opposite in sign to those with intramuscular fat, but were lower in magnitude. The lack of similar correlations between muscle
Fatty acid composition of lipid in Longissimus dorsi muscle of pigs
305
moisture content with intramuscular fat content and fatty acids in Landrace pigs (r = --0"36) was due to lower covariances of the latter traits, rather than to differences in the variation of muscle moisture content for Landrace (79.0 mg/g 2) and Duroc (89.6 mg/g 2) pigs. There were breed-sex differences for fatty acids C18:1 and C18:2 and the eating quality traits as Duroc gilts had higher levels of C18:1 but lower levels of C18:2, and Duroc boars had poorer flavour and tenderness than other breed-sex combinations, although Duroc pigs were tougher and juicier than Landrace pigs (Cameron et aL, 1990). Differences in intramuscular fat content in the various breed-sex classes accounted for approximately half of the differences in C18:1, C18:2 and tenderness. The differences between the breed-sex classes were not substantially reduced for flavour and juiciness at constant intramuscular fat content, but there was more of a reduction in Landrace pigs than there was in Duroc pigs. The poorer flavour of Duroc boars was, therefore, not due to differences in intramuscular fat content and is unlikely to be a function of the particular fatty acid composition of the intramuscular fat, as the overall fatty acid composition of Duroc boars was similar to that of Landrace gilts (Table 1). The higher concentration of 5~androst-16-en-3-one in Durocs compared with white breeds (Wood et al., 1988) may be the most likely cause of the poorer flavour score of Duroc boars. High androstenone levels have been associated with certain fatty acid compositions, but this relationship may be breed-specific (Malmfors et aL, 1978b). The similar negative relationships between all the polyunsaturated fatty acids, except C18:3, with flavour contrasts with other reports that changes in the concentration of C18:2 and C20:4, which is derived from C18:2, have little effect on flavour (Wahlstrom et al., 1971; H a r t m a n et aL, 1985). The low correlations between C18:3 with intramuscular fat content and flavour differs from other studies. Malmfors et al. (1978a) reported positive correlations between C18:3 and intramuscular fat content in Landrace and Yorkshire pigs. High concentrations of C 18:3 and possibly other n-3 fatty acids derived from C 18:3, have been associated with less desirable flavours in beef (Melton et al., 1982; Miller et aL, 1987). The absence of an effect on flavour of C18:3 in pigs may result from differences in the relative concentrations of C 18:2 and C 18:3 between the species. However, the tenderness of meat from Duroc pigs was largely due to a higher intramuscular fat content than for Landrace pigs. The main selection objective in pig breeding is efficient lean meat production but selection for leaner meat has been associated with reduced meat quality (Kempster et al., 1986) and reduced eating quality, but the latter was not substantiated in the study of Wood et al. (1986). An examination of the genetic parameters involving carcass lean, muscle and fat characteristics and eating quality traits (Table 5) will enable some quantification of the
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correlated responses in these traits to selection for improved carcass lean. In terms of phenotypic standard deviations, the magnitude of the proportional responses in muscle and fat characteristics and in eating quality traits relative to the response in carcass lean were approximately 0.29 for muscle fat and moisture content and muscle pH, and 0-16 on average for intramuscular fatty acids. The actual responses to selection for reduced backfat thickness (Wood et al., 1978) were higher C18:2 and lower C18:1 with increased drip loss, which were qualitatively consistent with the predicted responses. The relative responses were also in agreement with the results of Kempster et al. (1986) and W o o d et al. (1986), that there would be a measureable response in muscle and fat characteristics given selection to improve carcass leanness. The relative responses for eating quality traits were -0-07, --0.16 and - 0 - 2 4 for flavour, tenderness and juiciness, which were proportionally consistent with the study of Kempster et aL, (1986) where the differences between loin chops of lean and fat pigs were - 0 . 1 0 , - 0 . 2 0 and - 0 , 2 6 for flavour, tenderness and juiciness, respectively. W o o d et al. (1986) reported that the only statistically significant difference between lean and fat pigs was that juiciness was lower in lean pigs. The results from the current study suggest that the correlated responses in eating quality traits to selection for increased carcass leanness will primarily be a reduction in juiciness and, to a lesser extent, tenderness.
ACKNOWLEDGEMENTS The Meat and Livestock Commission and Dalgety Agriculture Ltd provided some of the funding for the experiment.
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