Characterization of Longissimus thoracis, Semitendinosus and Masseter muscles and relationships with technological quality in pigs. 2. Composition of muscles

Meat Science 94 (2013) 417–423

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Characterization of Longissimus thoracis, Semitendinosus and Masseter muscles and relationships with technological quality in pigs. 2. Composition of muscles C.E. Realini a,⁎, M. Pérez-Juan a, P. Gou a, I. Díaz a, C. Sárraga a, P. Gatellier b, J.A. García-Regueiro a a b

IRTA, Finca Camps i Armet, E-17121 Monells, Girona, Spain INRA, UR 370 QuaPA, F-63122 Saint Genès Champanelle, France

a r t i c l e

i n f o

Article history: Received 7 November 2012 Received in revised form 1 March 2013 Accepted 8 March 2013 Keywords: Longissimus Semitendinosus Masseter Quality Composition

a b s t r a c t The composition of three porcine muscles (Longissimus thoracis: LT, Semitendinosus: ST, Masseter: MS) was characterized and its link with muscle quality was evaluated. The LT muscle had a higher content of tyrosine, tryptophan, and carbohydrates and a lower content of vitamin E and haem iron than the MS muscle, while the ST had similar composition to MS but a lower content of haem iron. Large differences between muscles were observed in relative amounts of most of the major fatty acids. The LT muscle had higher saturated fatty acids (SFA) and n− 6:n−3 fatty acid ratio, and lower polyunsaturated fatty acids (PUFA), PUFA:SFA ratio, unsaturation index and average fatty acid chain length than the ST and MS muscles. Muscle pH, redness and chroma were positively correlated with vitamin E and unsaturated lipids and negatively correlated with tyrosine, tryptophan, carbohydrates and saturated lipids, whereas muscle lightness and expressible juice showed similar correlations but an opposite sign with these variables. © 2013 Elsevier Ltd. All rights reserved.

1. Introduction Meat and meat products contribute substantially to the human diet as a source of proteins with a high biologic value, essential fatty acids, vitamins (B group) and micronutrients (Zn, Se, Fe) (Higgs, 2000). World pork production occupied the first place in 2009 among other types of meat, representing 40% followed by poultry with 30% and beef with 23% (FAO, 2011). Iron deficiency in humans is one of the most common nutritional problems in both the developed and developing countries (Monsen, 1999), especially in neonates, fertile women and vegetarians. Meat consumption not only supplies haem iron which has higher bioavailability than vegetable non-haem iron (Hunt & Roughead, 2000), but also enhances non-haem iron absorption from other diet components (Mulvihill & Morrissey, 1998). However, pork meat is often controversial because it is considered that it contributes to an excess of fat, saturated fatty acids and cholesterol (Hernandez, Navarro, & Toldrá, 1998). Among the compositional traits related to meat quality, the quantity and nature of the muscle lipids are known to be very important (Fernandez, Mourot, Mounier, & Ecolan, 1995). It is well known that the predominant characteristic of a given muscle is determined by its relative composition in the different types of myofibres, and the lipid content and composition vary among the different pork muscles. However, there are still conflicting results with regard to the effect of muscle type on the content and composition of lipids. Generally, oxidative muscles contain more lipids and the lipids are less saturated than glycolytic ones (Cava, Estévez, Ruiz, & ⁎ Corresponding author. Tel.: +34 972 63 00 52. E-mail address: [email protected] (C.E. Realini). 0309-1740/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.meatsci.2013.03.007

Morcuende, 2003; Hernandez et al., 1998; Leseigneur-Meynier & Gandemer, 1991). In contrast, some authors found no association between total lipid content (Leseigneur-Meynier & Gandemer, 1991) or composition (Kang et al., 2011) and the type of muscular metabolism. In addition, Purchas, Morel, Janz, and Wilkinson (2009) indicated that there are some aspects of muscle composition for pork that have not received much attention because their possible importance from a nutritional perspective has only recently been appreciated, including some of the fatty acids present at low concentrations (Enser, 2001), and some muscle components other than fatty acids that have potential bioactive properties (Purchas, Rutherfurd, Pearce, Vather, & Wilkinson, 2004). As discussed by Realini et al. (2013), muscle models are needed to evaluate the effect of different processing parameters on the technological and nutritional qualities of meat. The European project ‘Design and development of REAlistic food Models with well-characterized micro- and macro-structure and composition’ (DREAM, 2013, 2009222654-2; Mackie et al., 2012) is developing food models for use as standards in food research and industry. More specifically, meat models are needed to understand reaction routes promoted by heating such as protein modifications (denaturation, oxidation, aggregation) which may have an impact on the nutritional value of meat (Gatellier et al., 2009). The present study was focused on the selection of well characterized meat categories which could be used as homogeneous ‘standard’ meat samples. Results concerning some structural characteristics of three porcine muscles (Longissimus thoracis, Semitendinosus, and Masseter) selected as meat categories and its relationship with technological quality were presented in a companion article (Realini et al., 2013). The objective of this study was to characterize the

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nutritional composition of these muscles and to evaluate its link with technological quality (pH, water holding capacity, instrumental colour) of meat. 2. Materials and methods 2.1. Animals and muscle samples Heads, loins and hams were obtained from carcasses of ten entire male [Pietrain × (Duroc × Landrace)] pigs reared under the same conditions on the same farm (carcass weight 89 ± 7 kg; lean percent 56 ± 3) at 24 h post-mortem from a commercial abattoir and transported to the IRTA-Monells centre in Spain. Longissimus thoracis (LT), between the 10th and 14th thoracic vertebra, and Semitendinosus (ST) muscles from the right-side of the carcass, and Masseter (MS) muscle from both right and left-sides of the carcass were excised at 48 h post-mortem from the loin, ham and head, respectively. LT and ST muscles were transversally cut from the cranial and the proximal end, respectively, into slices of different thicknesses: 4 cm for pH, instrumental colour, composition (moisture, fat, protein, collagen) and fatty acids, 1.5 cm for expressible juice, 2 cm for content determination of the different types of iron, 1 cm for aromatic amino acids, 1 cm for vitamin E content and 1 cm for the determination of total carbohydrates. MS samples were cut with the same thickness as the LT and ST muscles for pH, instrumental colour, composition and fatty acid determinations from the left-side of the carcass, while samples for expressible juice, vitamin E, aromatic amino acids, iron and total carbohydrate analyses were removed from the right-side of the carcass. 2.2. Meat quality traits Muscle pH, instrumental colour and expressible juice were determined as described by Realini et al. (2013). The ST muscle is not homogeneous in colour showing two major coloured zones. Thus, pH, expressible juice and instrumental colour parameters were determined in two areas of the ST, the dark and deep and the light and superficial parts of the muscle. Samples for the determination of meat composition were analyzed as described by Realini et al. (2013). Meat samples for the determination of fatty acids, vitamin E, aromatic amino acids, and iron content were vacuum packaged and stored at − 20 °C until analyses. 2.3. Chemical analysis Lipids were extracted using the chloroform–methanol procedure of Folch, Lees, & Stanley (1957). After evaporation of the extract, fatty acids were converted to fatty acid methyl esters (FAME) following the method ISO 5509-1978 (E) by using 14% BF3 in methanol, and analyzed by gas chromatography (Hewlett–Packard 5890 Series II GC, Avondale, PA, USA) in duplicate using tripentadecanoin (T4257, Sigma-Aldrich, Madrid, Spain) as internal standard. Individual fatty acids were identified by retention time with reference to standards (FA methyl ester mixture 189-19; Sigma-Aldrich, Madrid, Spain). Unsaturation index (UI) and average chain length (ACL) were calculated according to Cava et al. (2003) and the nutritional ratio was calculated as reported by Estevez, Morcuende, and Cava (2006) as indicated in Table 2. For the determination of tocopherols, muscle samples were extracted with a solution of n-hexane/2-propanol (3:2, v/v) by sonication. The obtained solutions were centrifuged and the supernatant was evaporated to dryness in a stream of nitrogen. The residue was redissolved in 1 ml of n-hexane/ethyl acetate (80:20, v/v) and 20 μl aliquot of the filtered extract was injected into the HPLC system. Samples and standards (5 and 10 ng/ml of α-tocopherol and δ-tocopherol in mobile phase) were analyzed by a normal phase in an Agilent Technologies HP 1100 system (Agilent, Palo Alto, CA, USA) equipped with

a fluorescence detector (FLD model 1046A, Hewlett Packard, Palo Alto, CA, USA). Chromatographic separation was performed on a Luna 3 μm, C18 (150 mm × 3 mm i.d.) column (Phenomenex, Torrance, USA). The mobile phase consisted of n-hexane/ethyl acetate (80:20, v/v) at a flow rate of 0.55 ml/min. Detection was carried out by fluorescence measurements (excitation wavelength = 290 nm, emission wavelength = 330 nm). Total carbohydrates were determined following the method of AOAC 958.06 (1980), using a spectrophotometer Shimadzu UV-1603 (Shimadzu Europa GmbH, Duisburg, Germany) at 630 nm, and results were expressed as the percentage of total glucose. The aromatic amino acid content was determined for phenylalanine, tyrosine and tryptophan using derivative spectrophotometry following the procedure described by Gatellier et al. (2009) and all measurements were performed in triplicate. Non-haem iron was measured spectrophotometrically by the Ferrozine method according to Carter (1971), and haem iron according to Hornsey (1956) as described by Realini et al. (2013). 2.4. Statistical analysis Analyses of variance were performed using the GLM procedure of SAS (SAS Inst. Inc., Cary, NC) with animal and muscle as fixed effects in the model and means separated by the Tukey's Studentized range test. Correlation Principal Component Analysis (PCA) was carried out using the JMP software (SAS Inst. Inc., Cary, NC) in order to evaluate the relationships between the technological quality and the chemical characteristics of the three pork muscles. Correlations among variables were computed by the CORR procedure of the SAS system. Muscle pH, expressible juice and instrumental colour data for the ST muscle were averaged across the light and dark coloured areas of the muscle for correlation analysis. 3. Results and discussion 3.1. Composition of muscles The samples used in this study were characterized using microscopy and meat quality characteristics and proximate composition as reported by Realini et al. (2013). Meat composition of aromatic amino acids, vitamin E, total carbohydrates, and iron is shown in Table 1 for LT, ST and MS pork muscles. Gatellier et al. (2009) indicated that the determination of aromatic amino acids is of great relevance to assess the nutritional value of meat since tryptophan and phenylalanine are essential amino acids for humans, and tyrosine can become essential in the diet of individuals living with phenylketonuria. In addition, cooking of meat favours protein oxidation and aromatic amino acids have been identified as particularly sensitive to the oxidative processes (Davies, 1987; Davies, Delsignore, & Lin, 1987). In turn, oxidations in meat induced by heating may limit amino acid bioavailability and are a leading cause of the decrease of nutritional value of meat (Gatellier et al., 2009). In bovine meat, Gatellier et al. (2009) have observed an important decrease of aromatic amino acids with increasing cooking times and temperatures and the indole ring of tryptophan was more stable to the heating treatments than the phenyl ring of phenylalanine and especially of tyrosine. These results are probably transposable to pork during heating. The oxidative degradation of aromatic amino acids depends on the pro- and anti-oxidant status of muscles which vary with the type of fibre. Therefore, the presence of natural antioxidants such as vitamin E, may be expected to have a role in the amino acid bioavailability from meat. No significant differences were detected among muscles in the content of phenylalanine, but the tyrosine percentage was higher in LT than ST and MS, and the tryptophan percentage was higher in LT than MS. Purchas et al. (2009) evaluated the chemical composition of pork muscles and found higher contents of tyrosine

C.E. Realini et al. / Meat Science 94 (2013) 417–423 Table 1 Content of aromatic amino acids, vitamin E, carbohydrates and iron of Longissimus thoracis (LT), Masseter (MS), and Semitendinosus (ST) pork muscles. Mean ± SD (n = 10). SEMA

Muscles LT

ST

MS

Aromatic amino acids, % Phe Tyr Trp

0.639 0.041a 0.017a

0.625 0.037b 0.016ab

0.667 0.037b 0.013b

0.015 0.001 0.0003

Vitamin E content, μg/g Total vitamin E Vitamin E, α Vitamin E, δ

3.02b 1.92b 1.10a

4.29a 2.65a 1.63a

4.16a 2.54a 1.62a

0.336 0.200 0.269

Total carbohydrates, %

0.43a

0.13b

0.19b

0.025

24.58a 5.09c

28.93a 9.69b

21.51a 14.02a

2.443 0.865

Iron content, mg/kg Total iron Haem iron

a

a

a

a,b,c Means within rows with common superscript letters are not significantly different (P > 0.05). A SEM: Pooled Standard Error of the Mean.

and phenylalanine relative to protein in Longissimus lumborum than Semimembranosus muscles, but tryptophan values were not reported. Tocopherols are lipophilic natural antioxidants, α-tocopherol is considered as the reference component with the highest biological power and δ-tocopherol is considered as the most active form in food systems. Fat content was higher in ST and MS than LT (Table 2). Thus, ST and MS had higher amounts of tocopherols than LT, although the differences were not significant (P > 0.05) in the content of δ-tocopherol (Table 1). Purchas et al. (2009) found no differences in vitamin E content between Longissimus lumborum and Semimembranosus muscles from pigs fed vitamin E supplements, but the fat percentage did not differ between muscles except for one of the four evaluated groups of animals. The percentage of total carbohydrates was higher (P b 0.05) in LT than ST and MS which did not differ (P > 0.05), consistent with the data reported by other authors (Fernandez & Tornberg, 1991; Karlsson, Klont, & Fernandez, 1999). No significant differences were detected in the total iron content among muscles, however, haem iron content was the highest in MS, intermediate in ST and the lowest in LT. Valenzuela, Lopez de Romana, Olivares, Sol Morales, and Pizarro (2009) reported a similar total iron content in major bovine cuts of meat. However, Purchas, Simcock, Knight, and Wilkinson (2003) reported lower total iron levels in the ST muscle of beef and lamb than in Longissimus or Triceps brachii muscles. Haem iron results are in agreement with those reported by other authors who showed the highest total haem pigment content for Masseter and the lowest for Longissimus dorsi (Cava et al., 2003; Laborde, Talmant, & Monin, 1985; LeseigneurMeynier & Gandemer, 1991), with intermediate values for a large number of other porcine muscles (Laborde et al., 1985; LeseigneurMeynier & Gandemer, 1991). In contrast, Purchas et al. (2009) found that the proportion of total iron as haem iron or as soluble iron did not differ significantly between Longissimus lumborum and Semimembranousus porcine muscles. Clark, Mahoney, and Carpenter (1997) pointed out that most literature on the mineral composition of foods contains only total iron analyses with no breakdown into the haem and non-haem iron fractions. Purchas et al. (2003) also indicated that there is information available in composition tables and elsewhere on the total iron content of different muscles, but there is limited information about the proportions of total iron in various forms and how these change between muscles. The authors highlighted the importance of the ratio haem to non-haem iron because iron within the haem molecule can be absorbed into

419

Table 2 Fatty acid composition (g per 100 g total fatty acids) of Longissimus thoracis (LT), Masseter (MS), and Semitendinosus (ST) pork muscles. Mean ± SD (n = 10). SEMB

Muscles Fatty acid

LT

ST

MS

c

0.95 0.96a 19.80a 0.25a 10.86a 0.13a 0.23b

a

2.34 0.64b 16.21b 0.25a 10.18a 0.13a 0.43a

1.73b 0.70b 13.86c 0.29a 10.64a 0.11a 0.29b

0.169 0.037 0.336 0.020 0.300 0.016 0.028

(n−9) (n−7) (n−9) (n−9) (n−7) (n−9) (n−9)

32.25a 0.57b 2.39a 1.97b 30.40a 3.81a 0.61a 0.79b

27.86b 1.19a 1.88b 5.60a 25.57b 3.44b 0.54b 1.08a

25.83c 1.32a 2.04b 5.85a 26.39b 3.65a 0.62a 1.12a

0.625 0.067 0.100 0.387 0.775 0.065 0.020 0.046

Σ MUFA C18:2 (n−6) C18:3 (n−6) C18:3 (n−3) C20:2 (n−6) C20:3 (n−6) C20:3 (n−3) C20:4 (n−6) C20:5 (n−3) C22:6 (n−3)

40.54a 18.75b 0.20a 0.58c 0.52c 0.74a 0.19a 5.50a 0.31b 0.46a

39.29a 23.40a 0.21a 0.85b 0.64b 0.78a 0.20a 5.77a 0.42a 0.52a

40.97a 23.41a 0.21a 0.97a 0.76a 0.80a 0.21a 6.05a 0.34ab 0.42a

1.062 0.581 0.010 0.029 0.022 0.033 0.008 0.265 0.028 0.037

Σ PUFA PUFA:SFA UIC ACLC

27.22b 0.85b 1.11b 17.72c

32.84a 1.19a 1.22a 17.80b

33.20a 1.29a 1.24a 17.84a

0.833 0.034 0.015 0.012

Nutritional ratioC n−6 n−3 n−6:n−3

0.39a 25.16b 1.55b 16.30a

0.32b 30.17a 2.02a 15.01b

0.27c 30.50a 1.94a 15.77ab

0.009 0.794 0.058 0.338

Total lipids C14:0 C16:0 C17:0 C18:0 C20:0 C21:0 Σ SFA C16:1 C16:1 C17:1 C18:1 C18:1 C20:1 C24:1

A

a,b,c Means within rows with common superscript letters are not significantly different (P > 0.05). A FoodScan™. B SEM: Pooled Standard Error of the Mean. C UI: unsaturation index (Σ(% each of unsaturated fatty acids × number of double bonds of the same fatty acid) / % total fatty acids). ACL: average chain length (Σ(% each of fatty acids × number of carbon atoms of this fatty acid) / % total fatty acids). Nutritional ratio: (12:0 + 14:0 + 16:0)/(18:1 + 18:2).

enterocyte cells in the wall of the small intestine by a process that is less affected by factors that inhibit the absorption of non-haem iron (Uzel & Conrad, 1998), thereby often making it more bioavailable. Absorption of iron from meat is typically 15 ± 25%, compared with 1 ± 7% from plant sources (Fairweather-Tait, 1989), and meat also enhances iron absorption from plant foods. Thus, the presence of meat in a meal can double the amount of iron absorbed from the other components of the meal (Higgs, 2000). Hunt and Roughead (2000) found that 22–26% of the haem iron content was absorbed from a meat containing diet whereas only 2–3% of the non-haem iron content was absorbed from the diet. Because of these great differences in bioavailability between the two forms of iron, the relative quantities of dietary non-haem and haem iron must be known to accurately estimate the total amount of bioavailable iron in a food (Clark et al., 1997). The significant differences in haem iron content among the evaluated pork muscles in the current study resulted in similar haem to non-haem ratios in LT and ST which were lower (P b 0.05) than the ratio in MS (0.29, 0.56, and 2.55 in LT, ST and MS, respectively), indicating that more iron could be absorbed from MS than ST and LT muscles. The intramuscular fat percentage and fatty acid composition of Longissimus, Semitendinosus and Masseter pork muscles are shown in

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Table 2. According to Cava et al. (2003), muscles have a different trend to intramuscular fat deposition, and their fatty acid composition varies depending on the types of fibre that constitute a muscle. The percentage of intramuscular fat was highest in ST, intermediate in MS and lowest in LT. Generally, glycolytic muscles contain less fat than oxidative ones (Fernandez et al., 1995; Hernandez et al., 1998; Karlsson et al., 1999; Taylor, 2004) because fast twitch fibres use carbohydrates whereas slow twitch fibres use lipids as the main energy source (Leseigneur-Meynier & Gandemer, 1991). However, other studies found that the association between total lipid content and type of muscular metabolism is not so clear, and Fernandez et al. (1995) indicated that the relationship between metabolic type and lipid content appears to depend on the muscles used. LeseigneurMeynier and Gandemer (1991) indicated that intramuscular lipid content as well as triglyceride content were not strictly related to the metabolic type, and that the glycolytic muscle Longissimus dorsi exhibited an intramuscular fat close to that of the oxidative muscle Masseter. Several authors have indicated that lipid composition, more specifically the phospholipid fraction, is one of the factors that have been reported to contribute to muscle variability (Cava et al., 2003; Fernandez et al., 1995; Leseigneur-Meynier & Gandemer, 1991; Sharma, Gandemer, & Goutefongea, 1987). The fatty acid composition of the intramuscular fat from the evaluated muscles in this study was significantly affected by the type of muscle. Intramuscular fat in LT muscle had higher proportion of total SFA, C14:0 and C16:0 compared with ST and MS, with no significant differences between muscles in C17:0, C18:0, and C20:0. Muscle percentage of C21:0 was higher in ST than MS and LT. There were no significant differences between muscles in the sum of all MUFA despite significant differences in the individual fatty acids. ST and MS muscles had similar percentages of C16:1 n− 9 and C17:1 and higher than LT. The percentages of C16:1 n− 7 and C18:1 n− 9 were higher in LT than ST and MS which did not differ (P > 0.05). C18:1 n− 7 and C20:1 were similar in MS and LT and higher than ST, while C24:1 was similar in ST and MS and higher than LT. ST and MS muscles had higher percentages of all PUFA, C18:2 n− 6 and C20:5 n− 3 than LT, with no differences between muscles in other PUFA except for C18:3 n− 3 which was higher for MS followed by ST and LT. Fatty acid composition results from this study are in agreement with those reported by Cava et al. (2003) who showed that the intramuscular fat from Longissimus dorsi contained less PUFA and was richer in oleic acid and SFA than the Masseter. Leseigneur-Meynier and Gandemer (1991) also reported higher percentage of SFA and lower of PUFA in Longissimus dorsi compared with Masseter, indicating that the PUFA and the total phospholipid contents increase with the oxidative activity of the muscles and appear to be strongly associated with the metabolic type. Differences in FA composition between muscles might be due to a higher number of cellular and sub-cellular membranes rich in phospholipids with high content of PUFA and the higher ratio of mitochondria to other membranes in oxidative compared with glycolytic muscles (Alasnier, Meynier, Viau, & Gandemer, 2000; Alasnier, Rémignon, & Gandemer, 1996; Leseigneur-Meynier & Gandemer, 1991). Hernandez et al. (1998) compared three muscles with different oxidative patterns and found a higher lipid content and a higher amount of phospholipids and PUFA in oxidative and intermediate muscles, Triceps brachii and Biceps femoris, than the glycolytic muscle Longissimus dorsi. The nutritional ratio was highest in LT, intermediate in ST and lowest in MS as a consequence of the higher degree of saturation of the intramuscular fat in LT compared with ST and MS muscles as indicated by the unsaturation index which was lower in LT than ST and MS. The average chain length was highest in MS, intermediate in ST and lowest in LT. Cava et al. (2003) also reported a higher unsaturation index and an average chain length in Masseter compared with the Longissimus dorsi muscle from pigs. Results from the present study show that total

intramuscular lipid and fatty acid composition appear to be associated with the metabolic type of the muscle. These variations in composition according to the respective metabolic pattern of the muscles may have an impact on muscle behaviour during storage, display or processing (Cava et al., 2003). The proportions of all intramuscular n−6 and n−3 fatty acids were similar in ST and MS and higher than LT. Nutritional recommendations for a healthy diet suggest that the ratio of PUFA to SFA (PUFA:SFA) should be 0.40, or higher, and the intakes of n−3 PUFA should be increased relative to n−6 PUFA. A value of 4.0 or less for the diet as a whole is recommended for the n−6:n−3 ratio (DH, 1994). In the present study, the PUFA:SFA ratio was similar in ST and MS and higher (P b 0.05) than LT, but all ratios were above the recommended value of 0.40 or higher. Pork is characterized by a high content of C18:2, which leads to acceptable PUFA:SFA ratios, but the high content in n− 6 fatty acids usually results in unfavourable n− 6:n− 3 fatty acid ratios for a healthy human diet. The n− 6:n− 3 ratio was lower (P b 0.05) in intramuscular fat from ST than LT while the ratio in MS was intermediate and did not differ (P > 0.05) from either muscle. However, the n− 6:n− 3 fatty acid ratio resulted well above the recommended value of less than 4.0 in intramuscular fat from all muscles. Beef, lamb and pork meats provide small amounts of some long chain n−3 PUFA: 20:3 n−6, 20:5 n−3, and 22:5 n−3, in contrast, it is one of the most important sources for C20:4 n−6 (Duo, Ng, Mann, & Sinclair, 1998; Rana & Sanders, 1986). The high level of arachidonic fatty acid (20:4 n−6) with values around 6% in the three muscles is close to the 5% reported by Hernandez et al. (1998) in Longissimus dorsi, Biceps femoris and Triceps brachii porcine muscles. In agreement with the very-long chain n−3 fatty acid data (EPA: eicosapentaenoic acid, C20:5; DPA: docosapentaenoic acid, C22:5, & DHA: docosahexaenoic acid, C22:6) reported by Purchas et al. (2009), no detectable DPA was found in the three evaluated muscles. Docosahexaenoic acid (C22:6 n−3) is an essential fatty acid in the development of the central nervous system in the new-born (Higgs, 2000). An amount of 200 mg of EPA plus DHA has been recommended for daily human intake (DH, 1994). Assuming a consumption of 100 g of meat plus 0.95, 1.73 and 2.34 g of fat from LT, MS and ST, respectively, intakes of EPA plus DHA would approximate to 7.32, 13.15, and 22.00 mg, respectively. Highest EPA plus DHA values were achieved in ST, intermediate in MS and lowest in LT, however, all values were well below the daily recommendation. 3.2. Relationships between meat quality traits and muscle composition Correlations (Table 3) and PCA (Fig. 1) were carried out to examine the relationships among meat quality and composition variables. High correlations (r > 0.5) were detected (P b 0.05) among variables. Muscle pH, redness and chroma were positively correlated with haem iron, vitamin E, fat, PUFA, PUFA:SFA and unsaturation index, and negatively correlated with total carbohydrates, tyrosine, tryptophan, SFA and the nutritional ratio. Expressible juice and colour lightness showed similar correlations with composition variables but with an opposite sign compared with pH, redness and chroma, with the exception of vitamin E which did not show a significant correlation with expressible juice. An overall view of these correlations is shown by means of the principal component plots for LT, ST, and MS porcine muscles. Fig. 1 shows a plot of meat quality and composition variables in the space generated by the first two principal components accounting for 69.4% of the total variation in the data (PC1: 51.2%, PC2: 18.2%). A group of variables can be distinguished composed by pH, redness, chroma, and haem iron located on the first PC far from the origin. The variables in this group are negatively correlated with expressible juice, lightness, total carbohydrates, tyrosine, and tryptophan, which show negative high values for the PC1. Another group of variables located on the first PC shows high positive values composed by n−6,

C.E. Realini et al. / Meat Science 94 (2013) 417–423

421

Table 3 Correlation coefficients (r) between meat quality and composition for the Longissimus thoracis, Semitendinosus, and Masseter porcine muscles (n = 30). VariablesA

pH

ExJuice

L*

a*

b*

C*

H°

Haem Fe Phenylalanine Tyrosine Tryptophan Total vitamin E Vitamin E, α Vitamin E, δ Carbohydrates Fat SFA MUFA PUFA PUFA:SFA n-6:n-3 UI NutRat

0.69⁎⁎⁎ 0.10 −0.68⁎⁎⁎ −0.74⁎⁎⁎ 0.49⁎⁎ 0.41⁎ 0.34 −0.76⁎⁎⁎ 0.57⁎⁎ −0.82⁎⁎⁎

−0.78⁎⁎⁎ −0.37⁎ 0.52⁎⁎ 0.67⁎⁎⁎ −0.23 −0.25 −0.11 0.39⁎

−0.76⁎⁎⁎ −0.20 0.67⁎⁎⁎ 0.75⁎⁎⁎ −0.44⁎ −0.52⁎⁎ −0.17 0.67⁎⁎⁎ −0.43⁎ 0.75⁎⁎⁎

0.82⁎⁎⁎ 0.16 −0.69⁎⁎⁎ −0.82⁎⁎⁎ 0.45⁎ 0.39⁎ 0.30 −0.63⁎⁎⁎ 0.43⁎ −0.78⁎⁎⁎

0.82⁎⁎⁎ 0.15 −0.69⁎⁎⁎ −0.82⁎⁎⁎ 0.46⁎ 0.40⁎ 0.31 −0.63⁎⁎⁎ 0.44⁎ −0.77⁎⁎⁎

−0.08 −0.57⁎⁎ −0.76⁎⁎⁎ 0.17 −0.61⁎⁎⁎ 0.83⁎⁎⁎

0.04 0.63⁎⁎⁎ 0.81⁎⁎⁎ −0.21 0.69⁎⁎⁎ −0.84⁎⁎⁎

0.26 −0.19 −0.37 −0.31 0.26 0.16 0.24 −0.34 0.48⁎⁎ −0.21 −0.23 0.39⁎ 0.32 −0.30 0.35 −0.18

−0.39⁎ −0.35 0.22 0.36 −0.06 −0.16 0.06 0.20 0.12 0.40⁎ −0.22 −0.15 −0.33 −0.13 −0.22 0.48⁎⁎

−0.19 0.67⁎⁎⁎ −0.01 −0.57⁎⁎ −0.72⁎⁎⁎ 0.024 −0.63⁎⁎⁎ 0.75⁎⁎⁎

0.27 0.46⁎ 0.74⁎⁎⁎ −0.35 0.56⁎⁎ −0.85⁎⁎⁎

0.03 0.63⁎⁎⁎ 0.81⁎⁎⁎ −0.22 0.69⁎⁎⁎ −0.84⁎⁎⁎

⁎ P b 0.05. ⁎⁎ P b 0.01. ⁎⁎⁎ P b 0.001. A Variables: expressible juice (ExJuice), lightness (L*), redness (a*), yellowness (b*), chroma (C*), hue angle (H°), SFA: saturated fatty acids, MUFA: monounsaturated fatty acids, PUFA: polyunsaturated fatty acids, UI: unsaturation index, NutRat: nutritional ratio.

of the variation. Variables displayed in the loading plot support the results obtained in previous studies. Hernandez et al. (1998) also found that meat with a high content in C18:2 has a reduction in oleic acid content, probably explained by the fact that linoleic fatty acid is the most potent inhibitor of the enzyme delta 9-desaturase, responsible for the oleic fatty acid synthesis (Jeffcoat & James, 1984). In the present

n−3, PUFA, C18:2, PUFA:SFA, and unsaturation index. These unsaturated fatty acid variables are negatively associated with the saturated fatty acid variables (SFA, C16:0, nutritional ratio) placed to the left in the loading plot. Long chain PUFA (C20:4, C20:5, and C22:6) with positive values and total MUFA and C18:1 with negative values are located on the second PC far from the origin, explaining an independent cause

1.0

C22:6n3 C20:4n6 n6 PUFA

C20:5n3 0.5

n3 NutrRat H°

CHO SFA Tyr L* Trp ExJuice

PC2 (18.2%)

C16:0

b*

P:S

C18:0 n6:n3

UI C18:2n6

HaemFe

0.0

Chroma a*

Phe Vitamin E Fat

C18:3n3 pH

-0.5

C18:1n9 MUFA -1.0 -1.0

-0.5

0.0

0.5

1.0

PC1 (51.2%) Fig. 1. Loading plot of the meat technological quality and selected composition variables onto the space defined by the first two principal components. Variables: expressible juice (ExJuice), lightness (L*), redness (a*), yellowness (b*), chroma (C*), hue angle (H°), haem iron (HaemFe), phenylalanine (Phe), tyrosine (Tyr), tryptophan (Trp), palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1n9), linoleic acid (C18:2n6), linolenic acid (C18:3n3), arachidonic acid (C20:4n6), EPA (C20:5n3), DHA (C22:6n3), saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), polyunsaturated fatty acids (PUFA), polyunsaturated to saturated fatty acid ratio (P:S), omega-6 fatty acids (n6), omega-3 fatty acids (n3), unsaturation index (UI), and nutritional ratio (NutrRat).

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8

L10

6

S10 4

L5 S7

S4 S5

M7

PC2 (18.0%)

2

S1

M5 S9 S M6 3 M M8 3 S8 M1 M4 M2 S2

L7 0

L8 -2

L1 L3 L4

L L2 6 L9

S6M10

M9

-4

-6

-8 -8

-6

-4

-2

0

2

4

6

8

PC1 (50.6%) Fig. 2. Score plot of the muscle samples onto the space defined by the first two principal components. Muscles: Longissimus thoracis (L), Semitendinosus (S), and Masseter (M). The subscript numbers identify the animals (n = 10) for each individual muscle sample.

study the percentage of C18:2 was higher in ST and MS than LT, while C18:1 was higher in LT than ST and MS in a percentage similar to C18:2 (Table 2). Fig. 1 shows that MUFA and C18:1 were negatively correlated with PUFA and C18:2. In agreement with the results reported by Hernandez et al. (1998), C18:2 was closely related with C20:4 since C18:2 is a precursor of the arachidonic acid (Kinsella, 1991). Tocopherols, mainly accumulated in adipose tissue, are closely linked with muscle fat percentage. The score plot (Fig. 2) shows the location of the LT, ST and MS samples identified by animal in the multivariate space of the two first principal component score vectors. The scores were arranged in the three muscle groups although the ST and the MS show certain variability with overlapping scores mainly situated in the positive axis of PC1 opposite to the LT group. The type of muscle is not clearly separated by PC2 and the data variation seems to be more associated with an individual animal effect or additional factors not related to the muscle type. 4. Conclusions The Longissimus thoracis muscle can be distinguished from the Semitendinosus and Masseter muscles since it presents a different pattern based on composition variables. The Longissimus thoracis muscle had higher tyrosine, tryptophan, and carbohydrates and lower vitamin E and haem iron content than the Masseter, while the Semitendinosus had similar composition to Masseter but a lower content of haem iron. Results also showed that the muscle metabolic type is related to the amount and fatty acid composition of the intramuscular fat. These results confirm that the glycolytic muscle Longissimus thoracis contained less lipids with more saturated fatty acids and less polyunsaturated fatty acids than the Semitendinosus and Masseter muscles. Muscle pH, redness and chroma were positively correlated with vitamin E and unsaturated lipids and negatively correlated

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