ARTICLE

Comparative Meat Qualities of Boston Butt Muscles (M. subscapularis) from Different Pig Breeds Available in Korean Market

Mahabbat Ali1https://orcid.org/0000-0002-5332-7758, Ki Ho Baek2https://orcid.org/0000-0002-5438-9547, Seong-Yun Lee1https://orcid.org/0000-0003-1361-1962, Hyun Cheol Kim2https://orcid.org/0000-0002-9445-7516, Ji-Young Park1https://orcid.org/0000-0001-9680-8685, Cheorun Jo2,3https://orcid.org/0000-0003-2109-3798, Jong Hyun Jung4https://orcid.org/0000-0003-3667-7710, Hwa Chun Park5https://orcid.org/0000-0001-8987-7789, Ki-Chang Nam1,*https://orcid.org/0000-0002-2432-3045
Author Information & Copyright
1Department of Animal Science and Technology, Sunchon National University, Suncheon 57922, Korea
2Department of Agricultural Biotechnology, Center for Food and Bioconvergence, and Research Institute of Agriculture and Life Sciences, Seoul National University, Seoul 08826, Korea
3Institute of Green Bio Science and Technology, Seoul National University, Pyeongchang 25354, Korea
4Jung P&C Institute, Yongin 16950, Korea
5Dasan Genetics, Namwon 55716, Korea
*Corresponding author : Ki-Chang Nam, Department of Animal Science & Technology, Sunchon National University, Suncheon 57922, Korea, Tel: +82-61-750-3231, Fax: +82-61-750-3231, E-mail: kichang@scnu.kr

© Korean Society for Food Science of Animal Resources. This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Received: Jul 07, 2020 ; Revised: Aug 26, 2020 ; Accepted: Sep 09, 2020

Published Online: Jan 01, 2021

Abstract

This study aimed to determine the effects of breed on meat quality characteristics of porcine Boston butt muscles (M. subscapularis) from three different pig breeds: Landrace×Yorkshire×Duroc (LYD), Berkshire, and Ibérico available in Korean market. Ibérico showed significantly higher fat content, yellowness (CIE b*), cooking loss, and lower shear force values than LYD and Berkshire. Moreover, the contents of oleic acid (18:1) and palmitic acid (16:0) were significantly higher in Ibérico breed, but stearic acid (18:0) was higher in LYD. As linoleic acid (18:2) and arachidonic acid (20:4) were higher in Berkshire sows as compared to the other breeds, atherogenicity and thrombogenicity indexes were significantly lower in Berkshire sow. Ibérico had lower the ω-6/ω-3 fatty acids ratio, and higher taurine and free amino acids compared with the others. Ibérico also showed significantly greater lipid oxidation, lower antioxidant capacity, and higher hypoxanthine contents, whereas the Berkshire had higher inosine-5’-monophosphate and lower K-index value as compared to the Ibérico. The breed did not impart any significant effect on the size and density of muscle fibers. Thus, quality characteristics of Boston butt varied from breed to breed, and certain consumer preferences for Ibérico can be explained, in part, by the unique quality characteristics imparted by higher contents of intramuscular fat, oleic acid, and free amino acids.

Keywords: breed; M. subscapularis; oleic acid; free amino acid; nucleotides

Introduction

Pork is an excellent source of quality proteins, important minerals, vitamins, and fat in the human diet (Li et al., 2013). To be cost-effective, pork quality is an important trait for consumers (Sosnicki et al., 2003). In the present days, Korean consumers prefer pork with relatively high marbling and redness scores. Interestingly, Korea has improved swine breeds in terms of production, and the current focus is now on improving pork quality traits across and within the available breeds (Li et al., 2013). Numerous researches have reported that pork quality traits are affected by the breeds and gender of the animals.

It is reported that muscle pH has a significant effect in different breeds, positively influencing meat quality traits such as meat color (Holmer et al., 2009), tenderness (Savel et al., 2005), and lipid oxidation (Hansen et al., 2004). It is well defined that pork with higher fat content has a significant effect on the ultimate pork quality, and is influenced by various factors (breed, sex, age, feed, species, and environmental conditions), imparting the pH, color, cooking loss, shear force, and sensory attributes (Choi et al., 2014). Higher muscle pH is a desirable trait for any pig breed since it influences certain meat quality parameters. In addition, it is well-documented that gender influences meat tenderness within and across the breeds. Increasing levels of soluble proteins in muscle enhances the binding strength of meat at processing, subsequently affecting the meat quality (Toldrá, 2008).

The fatty acid profile of porcine muscle is specific, independent in its functions, and is affected by several factors associated with the genetic background (breed), gender, age, fatness, body weight, dietary fatty acid composition, energy intake, and de novo synthesis of fatty acids (Wasilewski et al., 2011). Deposition and composition of muscle are highly heritable, and vary among and within breeds (Wood et al., 2004). Atherogenic and thrombogenic index are purportedly lipid quality indicators, depending on the contents of a particular group of fatty acids. They characterize the potential predisposition to atherosclerosis and thrombosis in humans, and have been used to assess the dietetic values of meat.

Meat freshness is a complex concept that includes physicochemical properties, biochemical attributes including biogenic amine, trimethylamine, and volatile amines (putresine, cadaverine epinephrine, dopamine, histamine), and microbiological spoilage (Gil et al., 2011). Despite the shortcomings that pork imported from other counties should have longer storage and freezing/thawing history resulting in less freshness than domestic pork, Ibérico’s preferences are increasing from certain Korean consumers. Nonetheless, a thorough investigation of physicochemical properties and pork freshness of Boston Butt (M. subscapularis) muscles of various pork varieties available on the Korean market has not been conducted. Therefore, considering the complexity of pork quality and freshness in the domestic pork market, the present study undertook to investigate the effect of the pig breed on the physicochemical properties of porcine Boston butt (M. subscapularis) muscles among the Landrace×Yorkshire×Duroc (LYD), Berkshire, and Ibérico.

Materials and Methods

Animals facilities and porcine samples

Boston butts (M. subscapularis) were randomly selected from the slaughterhouses (Namwon and Suncheon), among the most popular varieties in the Korean pork market. Each five carcasses (Quality grade 1) of LYD barrows, Berkshire sows, or Berkshire barrows weighing about 110 kg were used in the study. Ibérico (bellota) butts were obtained from a direct pork trade company importing from Spain. After collecting available pork samples, the muscles were kept at 4°C until sampled and analyzed for their physicochemical meat quality traits. Muscle fiber samples for analysis were prepared by cutting each muscle into 1.0×1.0×1.5 cm pieces in a direction parallel to the muscle fiber. The specimens were immediately frozen in isopentane chilled with liquid nitrogen, and stored at –70°C until histological analysis.

Proximate composition, pH, cooking loss, meat color, and shear force

Moisture contents of M. subscapularis muscle excised from the three different pig breeds were determined by drying the samples (3 g) at 102°C (AOAC, 2000). The crude protein content was measured by the method suggested by the (AOAC, 2000). Lipids were extracted from 5 g of muscle with chloroform/methanol (2:1), according to the (Folch and Lees, 1951). pH values of M. subscapularis were measured using a pH meter (Seven Excellence™, METTLER TOLEDO, Switzerland). The lightness (CIE L*), redness (CIE a*), and yellowness (CIE b*) of Boston butt samples from the different pigs were measured using a colorimeter (CR-410, Minota, Japan). All values of color were taken in triplicate for each sample. Shear force values were measured using a Warner-Bratzler shear attachment on a texture analyzer (TA-XT2, Stable Micro System, Surrey, UK).

Fatty acid composition and nutritional quality indices

The fatty acids composition of porcine M. subscapularis muscle was estimated by the method of (O’fallon et al., 2007), with a minor modification. The assay was performed using a Gas Chromatograph-Flame Ionization Detector (7890 series, Agilent, Santa Clara, CA, USA) under the following conditions: injector split mode with split ratio of 25:1, temperature 250°C. High purity air, high purity H2, and high purity He were used as carrier gases. The flow rate was maintained at 40 mL/min for H2 and 400 mL/min for air. An HP-88 column (60 m×250 μm×0.2 mm) was used for the analysis. Fatty acid composition is expressed as a percentage. The nutritional quality indexes of lipid for porcine M. subscapularis muscle were analyzed from the fatty acid composition data obtained for each group of pigs, according to the equations proposed by (Santos-Silva et al., 2002), as shown below:

Atherogenicity index (AI)=(C12:0 + 4×C14:0 + C16:0)/[MUFA+(ω-6)+(ω-3)]Thrombogenicity index (TI)=(C14:0 + C16:0 + C18:0)/[0.5×MUFA+0.5×(ω-6)+3×(ω-3)+(ω-3)/(ω-6)]

Analysis of free amino acids (FAA)

The soluble amino acids composition of porcine M. subscapularis muscle was determined by using a slightly modified method described by (Hughes et al., 2002). High performance liquid chromatography (HPLC) analyses of free amino acids were obtained using an S433 auto analyzer, cation separation column (LCAK07/li; 4.6×150 mm), buffer change (A, pH 2.90; B, pH 4.20; C, pH 8.00), lithium citrate buffer solution having a buffer flow rate 0.45 mL/min, ninhydrin flow rate 0.25 mL/min, and column temperature 37°C.

Lipid oxidation and antioxidant capacity

Lipid oxidation rate of the Boston butt porcine muscle (M. subscapularis) was assessed according to the procedure described by Ahn et al. (1998), with a slight modification in the thiobarbituric acid-reactive substances assay (TBARS). Anti-oxidant capacity of M. subscapularis porcine muscle from the three different pig breeds was determined by applying the free radical scavenging assay, according to a method described by Blois (1958), and is expressed as the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity (%). The porcine samples were inspected on d 1 and 7 of refrigeration at 4°C.

Muscle fiber size and fiber density

Muscle fiber characteristics were determined by the method of Choi et al. (2012) with slight modifications. Frozen muscles were cut into 10 μm thick transverse sections using a cryomicrotome (CM1860, Leica Biosystems, USA) at –20°C. Each sample was mounted on 76×26×1 mm adhesive microscope slides (HistoBond®, Paul Marienfeld GmbH & Co. KG, Lauda-Königshofen, Germany), coated with a drop of aqueous mounting medium (S3023, Dako, Carpinteria, CA, USA), and covered with a 22×22 mm coverslip (100 Deckglaser, Menzel-Glaser). All samples were viewed and photographed using a fluorescent microscope (BX51, Olympus, Tokyo, Japan) equipped with a DP72 digital camera (Olympus). Using a Photoshop CC (Adobe, California, USA), cross-sectional area (CSA; μm2) and muscle fiber density (fiber number/mm2) was determined from approximately 900 fibers per section.

Nucleotides contents

Nucleotide contents were determined by the method of Lee et al. (2017) with slight modifications. Briefly, the M. subscapularis muscle (5 g) was homogenized with 20 mL of 0.6 M perchloric acid. The homogenate was centrifuged at 2,265×g for 15 min (Continent 512R, Hanil, Incheon, Korea) and filtered through a filter paper (Whatman No. 4, Whatman PLC., Brentford, UK). The filtrate was titrated to pH 5.5 using 0.6 N and 6 N KOH. After titration, the samples were transferred to a volumetric flask and the resultant solution was filtered through a membrane filter (0.2 μm) into a glass vial. Nucleotides were quantified using HPLC (Ultimate 3000, Thermo Fisher Scientific, Waltham, MA, USA) with a SynergiTM Hydro-RP 80 Å column (250×4.6 mm, 4 μm particles; Phenomenex, Seoul, Korea). The 20 mM phosphate buffer (pH 5.5) was eluted at a flow rate 1.0 mL/min, detection wavelength 254 nm, and column temperature 30°C. The meat freshness indicator, known as the K-index, was determined using the ATP degradation nucleotides formula suggested by Gil et al. (2011):

Kindex=[Ino]+[Hx][IMP]+[Ino]+[Hx]×100

Statistical analysis

Data obtained were analyzed by multiple assay techniques, applying the Student-Newman-Keuls for significance test (p<0.05) using the general linear model of the SAS program (SAS, 2003). Significant differences were determined by applying the one-way ANOVA. Each treatment was performed in five replication (carcasses), and results are presented as the standard error of the means (SEM).

Results and Discussion

Proximate composition, color, pH, cooking loss, and shear force values

Proximate composition and meat quality characteristics (color, pH, cooking loss, and shear force value) of porcine M. subscapularis muscle were examined (Table 1). Results show that moisture contents ranged from 62.11% to 74.16%, with Ibérico pigs harboring significantly lower content than other breeds (p<0.05). However, previous studies have reported lower moisture contents ranging from 61.86% to 63.74% in pigs, which is similar to a study by Lim et al. (2014). It was demonstrated that the Ibérico pigs have a significantly higher lipid content as compared to other groups. The variation of fat content among groups is probably due to the breed effect (Stanišić et al., 2013). Moreover, the higher moisture loss in Ibérico pigs could be attributed to longer storage time under freezing conditions. The crude protein contents in Ibérico pigs were significantly higher than LYD pigs. Besides the ash content, no significant differences were found among the breeds. Our results indicate that except the yellowness value (CIE b*) of Ibérico pigs, the breed does not affect the overall meat color. The enhanced yellowness (CIE b*) for Ibérico pigs is associated with higher fat oxidation and pigment lability, as compared to other groups (Fernández‐Lopez et al., 2004). It is also noteworthy that Ibérico pigs significantly lost a higher amount of water during cooking than other breeds. It has previously been reported that lower cooking loss is associated with heavier pigs as compared to lighter animals (Magowan et al., 2011), and is also related to cooking processes, such as temperature and time at the heating phase (Madzimure et al., 2017). Considering the shear force value, M. subscapularis porcine muscle from Ibérico pigs show remarkably lower shear force value (kg.f) which is associated with more tender meat, as compared to other pig breeds (Table 1). Tenderer meat is related to proteolysis of muscles, specifically myofibrillar and cytoskeletal protein degradation including titin, desmin, nebulin, and troponin-T (Jeleníková et al., 2008). Meat tenderness is also affected by the origin of the animal as well as their age, breed, gender, and environmental conditions, and period of meat ageing (Ouali, 1990).

Table 1. Proximate composition and meat quality characteristics of porcine M. subscapularis muscle from LYD, Berkshire, and Ibérico pigs
Items LYD Berkshire sow Berkshire barrow Ibérico SEM1)
Moisture (%) 71.33b 74.16a 73.62a 62.11c 0.44
Crude protein (%) 19.38b 20.84ab 20.17ab 22.33a 0.87
Fat (%) 5.98b 4.91b 5.62b 13.72a 0.34
Crude ash (%) 1.06 1.08 1.06 1.04 0.03
CIE L* 43.25 45.83 47.03 51.42 2.41
CIE a* 16.98 18.62 17.41 20.52 1.12
CIE b* 7.48b 9.59b 8.70b 13.48a 0.98
pH 5.98 6.02 6.17 6.31 0.11
Cooking loss (%) 10.10b 11.96b 15.10b 27.00a 2.63
Shear force (kg.f) 4.82a 4.17a 3.12b 1.78c 0.37

a–c Values with different superscripts letters within the same row differ significantly (p<0.05).

1) n=12.

LYD, Landrace×Yorkshire×Duroc.

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Fatty acid analysis

The fatty acid composition of muscles is an important factor in determining the nutritional quality of meat or adipose tissue subjected with special attention in human health. In our study, we determined the free fatty acid composition of porcine M. subscapularis muscle from different pig breeds (LYD, Berkshire, and Ibérico) (Table 2). Our results reveal that the SFA content for Berkshire sow is significantly lower than other breeds (p<0.05). Conversely, Berkshire sow harbored a higher content of UFA than the LYD, Berkshire barrow, and Ibérico pigs. The predominant fatty acids, (18:1) and (16:0), were significantly higher in Ibérico M. subscapularis porcine muscle. Moreover, significantly higher levels of (18:2) and (20:4) were obtained in Berkshire sow, as compared to the other tested breeds. The PUFA/SFA (P/S) ratio of meat contributes a favorable balance between the ω-6/ω-3 PUFA; the recommended P/S value is greater than 0.4, although meat from some natural sources has a value of around 0.1 (Wood et al., 2004). The P/S values obtained from the three different pig breeds were 0.38, 0.58, 0.41, and 0.20 for LYD, Berkshire sow, Berkshire barrow, and Ibérico pigs, respectively. The ratio of ω-6/ω-3 unsaturated fatty acids of M. subscapularis porcine muscle was determined to be 14.32, 17.34, 14.45, and 7.71 for LYD, Berkshire sow, Berkshire barrow, and Ibérico pigs, respectively. The significantly lower ratio of ω-6/ω-3 fatty acid noted for Ibérico M. subscapularis porcine muscle attributes as a desirable characteristic in terms of reducing chronic diseases, especially blood clot formations leading to heart attack, in humans (Wood et al., 2004). The recommended ω-6/ω-3 ratio is less than 4.00; however, some meats are higher than the recommended level which, however, can be manipulated by maintaining the P/S ratio in meat. The differences observed in the study were associated to breed effect and different genetic factors. In Berkshire barrow, the SFA level was higher than the Berkshire sow (p<0.05), which was in agreement with results reported by Kasprzyk et al. (2015). However, PUFA levels in the Berkshire sow were significantly higher than other breeds (p<0.05), mainly due to the high content of linoleic acid (Table 2). We infer that the higher ω-6/ω-3 ratio is due to the excessive saturated fat and lower levels or deficiency of ω-3 fatty acids in the diet, as well as the influence of breed attributes (Enser et al., 2000).

Table 2. Fatty acid composition and lipid quality indexes of porcine M. subscapularis muscle from LYD, Berkshire, and Ibérico pigs
Items (%) LYD Berkshire sow Berkshire barrow Ibérico SEM1)
10:0 0.11a 0.10ab 0.12a 0.09b 0.00
12:0 0.14a 0.15a 0.14a 0.08b 0.01
14:0 1.52 1.52 1.55 1.46 0.07
16:0 23.81b 22.22b 23.47b 25.53a 0.35
16:1 2.28b 2.94a 2.97a 3.54a 0.12
18:0 13.38a 9.87c 11.53b 10.07c 0.26
18:1 40.08b 38.47b 40.68b 48.81a 0.75
18:2 12.07b 15.81a 12.39b 5.74c 0.61
18:3 0.75 0.73 0.75 0.78 0.02
20:2 0.42a 0.52a 0.44a 0.23b 0.03
20:3 0.23b 0.34a 0.23b 0.09c 0.02
20:4 1.49b 2.27a 1.35b 0.65c 0.15
24:1 0.33b 0.46a 0.34b 0.12c 0.02
∑SFA 38.96a 33.86b 36.80a 37.23a 0.56
∑UFA 57.65c 61.55a 59.14bc 59.95b 0.45
∑MUFA 42.70b 41.87b 43.98b 52.46a 0.80
∑PUFA 14.96b 19.68a 15.15b 7.49c 0.74
UFA/SFA 1.48b 1.82a 1.61b 1.61b 0.04
PUFA/SFA 0.38b 0.58a 0.41b 0.20c 0.02
∑ω-6 13.98b 18.61a 14.18b 6.62c 0.73
∑ω-3 0.98ab 1.07a 0.98ab 0.87b 0.03
ω-6/ω-3 14.32b 17.34a 14.45b 7.71c 0.60
AI 0.52a 0.46b 0.51a 0.52a 0.01
TI 1.24a 1.01b 1.14a 1.15a 0.02

a–c Values with different superscripts letters within the same row differ significantly (p<0.05).

1) n=12.

LYD, Landrace×Yorkshire×Duroc; SFA, saturated fatty acid; UFA, unsaturated fatty acid; MUFA, monounsaturated fatty acid; PUFA, polyunsaturated fatty acid; AI, atherogenicity index; TI, thrombogenicity index.

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Lipid quality indexes

The nutritional quality indexes of lipid for M. subscapularis porcine muscle excised from three different pig breeds were evaluated (Table 2). Ulbricht and Southgate, (1991) reported that the atherogenic or hyperlipidemic SFAs are (C12:0), (C14:0), and (C16:0) acids, while (C14:0), (C16:0), and (C18:0) acids are thrombogenic SFAs. The long chain unsaturated fatty acids, especially ω-6 (linoleic) and ω-3 (linolenic) fatty acids, are thought to be anti-atherogenic and anti-thrombogenic, indicating that diets should contain lower index values to reduce human cardiovascular diseases (Cebulska et al., 2018). Lower atherogenicity index (AI) value represents a lower proportion of saturated to unsaturated fatty acids, which subsequently reduces the endothelial strength of blood vessels owing to collapsed lipids and plaque formation (Cebulska et al., 2018). Conversely, lower thrombogenicity index (TI) values determined from the proportion of other fatty acids, indicates a lower risk of disturbance to blood coagulation and clotting. In the current study, AI and TI index values obtained were 0.52, 0.46, 0.51, 0.52, and 1.24, 1.01, 1.14, 1.15, respectively, for LYD, Berkshire sow, Berkshire barrow, and Ibérico pigs, respectively. These results indicate that Berkshire sow has significantly lower AI and TI values, as compared with other tested breeds (p<0.05); this could be attributed to the higher content of unsaturated fatty acids.

Free amino acids

The free amino acids composition of porcine M. subscapularis muscle of the three different pig breeds was analyzed (Table 3). It has previously been classified that lysine, leucine, isoleucine, valine, phenylalanine, histidine, methionine, and threonine are the essential amino acids, whereas aspartic acid, serine, arginine, glutamic acid, tyrosine, glycine, and alanine are non-essential amino acids. Previous studies report that except lysine and histidine, all essential amino acid levels were significantly higher in Ibérico pigs as compared to other breeds (p<0.05). Taurine, the functional compound related to ATP production in muscles, was significantly higher in the Ibérico pigs. However, the glutamic amino acid which imparts the umami taste in meat, was significantly higher in LYD pigs as compared to Ibérico pigs (Wood et al., 2004). In the present study, amino acid levels were higher in Ibérico pigs than other breeds, and enriched with almost all essential amino acids, an important factor for eating quality and also imparting numerous health benefits for meat consumers (Subramaniyan et al., 2016). The increment of amino acids in Ibérico pigs can be attributed to breed effect, which depends on the amino peptidase and hydrolytic activity toward increased group with the proteolysis of muscle by enzyme known as calpain (Feidt et al., 1996; Nishimura et al., 1988). Moreover, Ibérico pigs harbor a higher amount of the total tasty and bitter amino acids, as compared with LYD, Berkshire sow, and Berkshire barrow pigs (p<0.05).

Table 3. Free amino acids of porcine M. subscapularis muscle from LYD, Berkshire, and Ibérico pigs
Free AA (mg/100 g) LYD Berkshire sow Berkshire barrow Ibérico SEM1)
Taurine 608.65b 640.60b 597.73b 758.73a 32.29
Aspartic acid 193.99 167.27 178.35 164.58 16.93
Threonine 66.26b 68.21b 61.06b 155.58a 3.14
Serine 75.72b 100.25b 98.37b 239.59a 6.09
Asparagine 107.84b 105.80b 95.34b 142.85a 8.59
Glutamic acid 663.40a 465.70ab 384.93ab 251.83b 87.49
Glycine 297.30b 286.15b 295.57b 414.04a 15.14
Alanine 513.90b 447.36b 483.17b 950.96a 28.03
Valine 52.87b 54.74b 55.11b 145.18a 7.91
Methionine 19.98b 18.46b 21.78b 57.08a 3.07
lsoleucine 26.92b 30.52b 29.79b 100.59a 3.47
Leucine 67.00c 86.96b 82.14b 228.34a 4.55
Tyrosin 34.61b 38.04b 41.50b 51.22a 2.71
Phenyalanine 37.96b 37.57b 35.47b 104.00a 2.13
Tryptophan 398.81ab 466.76a 394.62ab 337.08b 23.81
Carnorsine 9.33 215.39 101.9 155.91 84.22
Lysine 46.96 136.79 73.66 106.62 28.17
Ammonia 117.19 161.46 93.82 141.8 34.1
Arginine 72.54 70.6 16.39 65.39 34.56
Histidine 15.36 3.53 1.67 15.4 6.63
∑Tasty AA 2,507.76b 2,349.93b 2,207.08b 3,029.21a 136.25
∑Bitter AA 277.27b 298.85b 240.69b 700.59a 34.43
Tasty/bitter AA 9.88 8.16 9.26 4.33 1.35

a–c Values with different superscripts letters within the same row differ significantly (p<0.05).

1) n=12.

AA, amino acids; LYD, Landrace×Yorkshire×Duroc.

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Oxidative stability

We examined the oxidative stability (lipid oxidation) of M. subscapularis muscle excised from LYD, Berkshire sow, Berkshire barrow, and Ibérico pigs (Table 4). Lipid oxidation value was significantly higher for Ibérico pigs at both d 1 and 7 of storage, compared to other breeds, as determined by the TBARS value, which revealed a significantly increasing trend with increasing d of storage. Lipid oxidation is one of the primary causes for loss in meat quality, and generates the volatile compounds responsible for rancidity of fresh meat (Gray et al., 1996). Lipid oxidation results in deterioration of some meat quality traits like flavor, texture, and color, and also decreases the shelf life, along with the production of some toxic compounds (Mohamed et al., 2008). In addition to lipid oxidation, it is postulated that muscles with higher fat content in between or across the muscles, show a greater tendency to be oxidized via a continuous free-radical chain reaction (Ruban, 2009). The oxidation rate of post-mortem muscle depends on the antioxidant capacity existing in the muscle of the animal, which can be retarded by the action of endogenous antioxidant enzymes, and differ among different species, different breeds, and or even among animals of a single species (Ren et al., 2013).

Table 4. Lipid oxidation expressed as TBARS value and antioxidant activity expressed as DPPH radical scavenging activity of porcine M. subscapularis muscle from LYD, Berkshire, and Ibérico pigs at different storage period
Items LYD Berkshire sow Berkshire barrow Ibérico SEM1)
TBARS (mg MDA/kg)
 1 d 0.20by 0.16by 0.15by 0.35ay 0.02
 7 d 0.54dx 0.56cx 0.59bx 0.75ax 0.00
 SEM1) 0.00 0.02 0.01 0.00
DPPH radical scavenging activity (%)
 1 d 50.89a 52.73a 49.27a 43.06bx 1.37
 7 d 50.51a 50.51a 52.56a 38.95by 1.27
 SEM1) 0.81 1.00 1.39 0.59

a–d Values with different superscripts letters within the same row differ significantly (p<0.05).

x–y Values with different letters within the same column differ significantly (p<0.05).

1) n=12.

TBARS, thiobarbituric acid-reactive substances; DPPH, (2,2-diphenyl-1-picrylhydrazyl) radical scavenging activity; LYD, Landrace×Yorkshire× Duroc.

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Antioxidant capacity

Antioxidants are compounds which combat free radicals in the system by intervening in any of the three steps of lipid oxidation, viz., initiation, propagation, and termination (Cui et al., 2004). The total antioxidant capacity of the M. subscapularis porcine muscles collected from three different pig breeds was measured by performing the free radical scavenging assay (Table 4), and was found to be affected by pig breeds. Ibérico pigs had lower antioxidant capacity compared to LYD, Berkshire sow, and Berkshire barrow at d 1 and 7 of storage (p<0.05). Except the Ibérico pig meat, all other tested groups presented no significant differences between the two storage conditions. Free radical inhibition percentage ranged from 43.06% to 52.73% and 38.95% to 52.56% for d 1 and 7, respectively. In Ibérico pigs, the free radical scavenging activity showed a decreasing trend with increasing number of d. Higher MDA compounds in Ibérico pigs revealed a higher content of lipids that deteriorate the quality of meat, thereby indicating lower antioxidant capacity. Apart from the MDA compounds, the antioxidant activities are also affected by endogenous, non-enzymatic antioxidants, breed, diet, and muscle types (Králová, 2015).

Muscle fiber size and fiber density

Examination of the muscle fiber size and fiber density of porcine M. subscapularis from LYD, Berkshire sow, Berkshire barrow, and Ibérico pigs showed no significant variation among the breeds (Table 5). Furthermore, different genders within breeds also had no significant impact on the muscle fiber size and fiber density. Moreover, the muscle fiber number is determined before birth genetically, and only the length and cross sectional area of the muscle fibers increases with age (Wigmore and Stickland, 1983). In addition, it is postulated that the total number, density, and size of different muscle fiber area as well as their composition are important histochemical attributes which impact the fresh meat or cooked meat during conversion from muscle to meat (Joo and Kim, 2011). Considering the muscle fiber density and fiber size, it has been determined that muscle fiber size positively correlates with the carcass weight, backfat thickness and loin eye area, whereas fiber density has a negative correlation in pork quality traits (Ryu et al., 2004). The density, compactness, and space of muscle fiber have been shown in Fig. 1. In our study, breed of the pigs imparted no effect on muscle fiber size and density. More research on muscle fiber types and composition is required to clarify the effect of breed on meat quality traits.

Table 5. Muscle fiber size and fiber density of porcine M. subscapularis muscle from LYD, Berkshire, and Ibérico pigs
Items LYD Berkshire sow Berkshire barrow Ibérico SEM1)
Muscle fiber density (fiber number/mm2) 170.11 183.39 197.42 180.02 9.37
Muscle fiber size (CSA) (μm2) 5,949.81 5,558.32 5,215.65 5,638.26 296.38

1) n=12.

LYD, Landrace×Yorkshire×Duroc; CSA, cross-sectional area.

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kosfa-41-1-71-g1
Fig. 1. Optical microscopic structure of porcine M. subscapularis muscle from LYD, Berkshire, and Ibérico pigs. LYD, Landrace×Yorkshire ×Duroc.
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Nucleotides contents

The nucleotide contents of porcine M. subscapularis muscle from LYD, Berkshire sow, Berkshire barrow, and Ibérico pigs were determined and are presented in Table 6. Ibérico pigs harbored significantly higher amounts of AMP and hypoxanthine than Berkshire sow and LYD pigs (p<0.05). AMP content differed depending on the animal age, sex, quality grade, and different cuts, possibly due to higher nucleotide contents. Regardless of the sex, Berkshire pigs had significantly higher IMP compared to Ibérico pigs (p<0.05). Nucleotides, AMP, GMP, and IMP are related to the umami and savory taste, while inosine and hypoxanthine impart the bitter taste (Dashdorj et al., 2015). Moreover, IMPs are important metabolites in meat flavor due to the synergistic effect with glutamic acid via the maillard reaction (Lee et al., 2017). The decomposition of ATP in different muscles is considered the most useful and reliable approach to evaluate the correct meat freshness. Owing to ATP decomposition, the analysis is based on the concept that after exemplification of pork, the ATP in meat decomposes in the following sequence: ATP-ADP-AMP-IMP-Ino-Hx (Hernández-Cázares et al., 2010). During these consequential changes, the smell and taste of meat also changes at different intervals. A similar autolytic process takes place in all animal, with variation among the different species. The concentration of ATP alone cannot be implied to measure the freshness index of meat, since it disappears within approximately 24 hours after post-mortem (Karube et al., 1984). In addition, a similar disappearing phenomenon is also observed for ADP and AMP. However, ATP degradation products generated have been suggested as indicators of meat freshness, and hence the concept of K-index was developed and introduced by Gil et al. (2011). Low K-index value is considered to indicate fresher meats than higher values. We therefore determined the K-index value of porcine M. subscapularis muscle from LYD, Berkshire sow, Berkshire barrow, and Ibérico pigs (Table 6). The K-index value of LYD, Berkshire sow, Berkshire barrow, and Ibérico pigs were found to be 79.92, 70.55, 66.80, and 94.21 respectively. Table 6 shows that LYD and Berkshire pigs presented with significantly lower K-index value than Ibérico pigs (p<0.05). Thus, the significantly lower K-index and hypoxanthine content of Berkshire M. subscapularis muscle indicates meat quality close to freshness and superior to Ibérico pigs (Hernández-Cázares et al., 2010; Nishimura et al., 1988).

Table 6. Nucleotide contents and K-index of porcine M. subscapularis muscle from LYD, Berkshire, and Ibérico pigs
Items LYD Berkshire sow Berkshire barrow Ibérico SEM1)
Nucleotide contents (mg/100 g)
 AMP 4.64b 4.28b 5.16ab 5.72a 0.23
 GMP 2.21 2.41 2.26 1.43 0.29
 IMP 68.35a 103.82a 104.45a 28.47b 10.51
 Inosine 43.90 49.07 48.31 35.78 5.87
 Hypoxanthine 88.73b 71.95b 57.84b 160.76a 9.44
K-index2) (%) 79.92b 70.55b 66.80b 94.21a 3.37

a,b Values with different superscripts letters within the same row differ significantly (p<0.05).

1) n=12.

2) K-index = [Inosine] + [Hypoxanthine] / [IMP] + [Inosine] + [Hypoxanthine] × 100.

LYD, Landrace×Yorkshire×Duroc; AMP, adenosine-5’-monophosphate; GMP, goanosine monophosphate; IMP, inosine-5’-monophosphate.

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Conclusion

The current investigation demonstrates that breed has a significant impact on pork quality due to the genetic makeup, nutrient composition, and muscle rheological properties. Meat quality traits such as fat content, yellowness, and cooking loss were significantly higher, and shear force value was lower in Ibérico pork, as compared to others. In addition, meat from Ibérico pigs had significantly lower ω-6/ω-3 ratios than LYD or Berkshire, while the content of free amino acids, taurine, and oleic was significantly higher. As a result, compared to other pig breeds, Ibérico pigs have the desired characteristic meat quality attributes for consumers who want highly marbled meat. However, Berkshire pigs had fresher values (lower K-index) as compared to other breeds. Therefore, a systematic evaluation of the breeding effects among meat quality parameters of Ibérico pigs can be used for further studies to improve high marbled pork.

Conflicts of Interest

The authors declare no potential conflicts of interest.

Acknowledgements

The work was financially supported by IPET agricultural life industry technical development project (318022-04-1-SB010).

Author Contributions

Conceptualization: Park HC, Jung JH. Data curation: Jo C, Nam KC. Formal analysis: Ali M, Baek KH, Lee SY, Kim HC, Park JY. Methodology: Baek KH, Lee SY, Kim HC, Park JY. Validation: Jo C, Nam KC. Writing - original draft: Ali M, Baek KH. Writing - review & editing: Ali M, Baek KH, Lee SY, Kim HC, Park JY, Jo C, Jung JH, Park HC, Nam KC.

Ethics Approval

This article does not require IRB/IACUC approval because there are no human and animal participants.

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