Meat quality parameters of wild boar and commercial pig breeds

A b s t r a c t: In recent decades pork production has increased in Serbia, and pork is the most widely consumed meat. Pig meat quality is affected by several factors: breed, sex, production performance, stress adaptation, and factors related to animal management. The aim of this study was to compare the meat quality characteristics from wild boar and pig breeds improved by selection. Samples of m. longissimus dorsi were obtained from three different pig breeds — Yorkshire, Landrace and wild boar. Chemical composition, pH, fatty acid profile, volatile compounds, color, and overall sensory meat quality were determined. Chemical composition, pH, fatty acid profile, and volatile compounds differed significantly (p<0.05) among the pig breeds. Yorkshire meat had the most favorable ratio of unsaturated to saturated fatty acids and the highest nutritional value. On the other hand, wild boar meat had the lowest intramuscular fat content. Determined differences among different pig breeds indicated the impact of breed on meat quality of pork. The results obtained could be used to meet consumer’s needs regarding fatty acid composition and sensory properties of meat.


Introduction
Pork is the most commonly consumed meat in Serbia. Pork accounts for 66.2% of meat production, followed by beef (31%), poultry (14.4%), and sheep and goat meat (8.4%) (Statistical Office of the Republic of Serbia, 2019). Furthermore, pig production is almost entirely based on Yorkshire and Landrace breeds that are used for production of F1 gilts and further cross-breeding with some of the terminal meat pig breeds, such as the Pietrain, Duroc and Hampshire.
Meat from Landrace and Yorkshire pigs, the most common pig meat breeds farmed in Serbia, is available in trade markets, while wild boar meat is mainly prepared as traditional products for the hunters' own consumption, or is sold through local restaurants, agritourism or semi-legal direct marketing (Stevanović and Milosević, 2018). Wild boar meat is of increasing importance in human nutrition worldwide due to consumers' preference for lean meat. It is considered as naturally organic and is highly appreciated. Wild boar meat is characterized by higher heme iron content and lower fat level than meat from domestic pig breeds. In many studies, a low fat content was determined in wild boar meat (2.62% (Szmańko et al., 2007); 2.27% (Jukna and Valaitienė, 2012); 1.8 %-3.5% (Postolache et al., 2011); 2.82% (Strazdina et al., 2013); 1.87% (Ivanovic et al., 2013)), but low total fat did not contribute to a beneficial ratio of saturated to unsaturated fatty acids.
On the other hand, some of the major breeding goals are to reduce carcass fatness, fattening time, and feed to gain ratio (Furman et al., 2010). Achieving these goals can provoke changes in fatty acid profiles of intramuscular fat. Furthermore, intramuscular fat cannot be removed before consumption. Nowadays, consumer concerns about the quality and healthfulness of meat and meat products have greatly increased during recent decades (Min and Ahn, 2005), especially regarding the health impact of consumed animal fats. The recommended ratio between all polyunsaturated to saturated fatty acids in human diets is 0.4 or higher (Wood et al., 2008), and the total fat intake should provide 15-30% of total energy intake or less (FAO, 2010).
Pig meat quality is affected by several factors, including biological factors: breed, sex, production performance, and stress adaptation, along with; factors related to production systems: environmental conditions, animal management, nutrition, and body Original scientific paper Meat quality parameters of wild boar and commercial pig breeds weight; slaughter factors and; treatment of carcasses after the slaughter (Kasprzyk, 2007;Ivanović et al., 2012;Mukumbo et al., 2014;Nuernberg et al., 2015;Čobanović et al., 2016;Cirne et al., 2019).
The aim of this study was to compare meat quality parameters (chemical composition, pH, fatty acid composition, volatile compound content, color, and sensory properties) for wild boar meat and meat from two commercial breeds (Landrace and Yorkshire).

Materials and Methods
All the experimental procedures and animal handling used in this study were in accordance with European Community guidelines (Directive 86/609/EEC).

Animals and sampling
A total of 30 male pigs were included in the study: 10 castrated Yorkshire pigs, 10 castrated Landrace pigs, and 10 wild boars. All Yorkshire and Landrace pigs were bred under the same environmental and feeding conditions. Compositions of feed mixtures are presented in Table 1. Animals were slaughtered at final live weight of 89-93 kg, at the age of 180 days. The animals were slaughtered in accordance with legally approved procedures (the distance from the farm to the slaughterhouse was 200 km, pigs underwent a rest period of about 2 h in the lairage, and automatic electric stunning and exsanguination in a vertical position were used). After evisceration and washing, pig carcasses were chilled at 2°C for up to 24 h. Samples of m. longissimus Legend: VG60 -minimum 5.0% protein, minimum 60.0% fat, maximum 0.8% cellulose, maximum 1.2% ash, minimum 7.5% linoleic acid, energy 24.0 MJ/kg dorsi were collected and stored at -20°C until determination of chemical composition, fatty acid content, volatile compound content, color, and sensory analyses.
Hunted wild boars weighed between 120 and 140 kg and were about one year old. Animals were hunted by shotgun during the hunting season in 2018 in accordance with the hunting law in Serbia (Official Gazette, 18/2010 and95/2018), and the carcasses were not polluted by digestive tract contents. Carcasses were eviscerated in the 24 h after hunting, and were marked according to Regulation 853 (2004) and854 (2004). Ten samples of m. longissimus dorsi were collected and stored at -20°C until determination of chemical composition, fatty acid content, volatile compound content, color, and sensory analyses. Wild boars were hunted from the southwest and southeast parts of the Šumadija region in Serbia. Nutrition of wild boars was determined by the region's feed sources, which primarily consisted of deciduous trees  oak, elk, linden, Austrian oak, chestnut and hazel. Herbaceous species in the region were dominated by Graminaceae, Asteraceae, and Poaceae, and corn, wheat, and barley were the most common species of grains (Jovanović, 1992). This region is also known for fruit cultivation  apple, plum, pear, apricot, peach, and cherry, which form a significant part of wild boars' diets.

Chemical composition of meat
Moisture content was determined by ISO 1442 (1998), fat content by ISO 1443 (1992) and ash content by ISO 936 (1999). The protein content was calculated by multiplying the nitrogen content by 6.25 using ISO 937 (1992), and pH, at 45 min post-mortem, was measured by ISO 2917 (2004).

Fatty acids in meat
The AOAC (2001) method was applied for lipid extraction from the tissue. After lipid hydrolysis, the fatty acids were esterified to methyl esters, evaporated to dryness in a stream of nitrogen and stored at -18°C. Analysis of fatty acid methyl esters (FAMEs) was performed by an internal standard method using a gas chromatograph (GC6890N, Agilent Tech., USA) with column DB-23 (60 m × 0.25 mm ID, 0.15 μm) and comparing peak areas and retention times with a standard mix of FAMEs 37 (Supelco, USA). Conditions of analyses: detector temperature = 250°C; injector temperature = 225°C; column temperature = 200°C; carrier gas = helium; carrier gas flow rate = 50 mL/min. Data obtained for fatty acid composition were expressed as a percentage by weight of the identified total fatty acids.

Volatile compounds in meat
Volatile compound analysis was conducted using the Likens-Nickerson extraction procedure (Likens and Nickerson, 1964) and ISO 15303 (2001) using a GCMS-QP2010 Ultra (EIMS, electron energy = 70 eV, scan range = 30-350 amu, and scan rate = 3.99 scans/s) with a SUPELCOWAX ® 10 capillary GC column (30 m × 0.25 mm ID, particle size 0.25 μm). The carrier gas was helium with a flow rate of 1 mL/min, and the injection temperature was 200°C. The oven temperature was programmed to initially hold for 10 min at 40°C, and subsequently programmed from 40 ºC to 120 ºC at a rate of 3 ºC/ min and at a rate of 10 ºC/min from 120 ºC to 250 ºC where it was held for another 5 min. Identification of the peaks was based on comparison of their mass spectra with the spectra of the WILEY library and in addition, in some cases, by comparison of their retention times with those of standard compounds.

Meat color
Meat color was measured on m. longissimus dorsi at 45 min post-mortem. CIE L*a*b* (CIE Colorimetry, 1986) color coordinates were determined using a Minolta Chromameter CR 400 (Minolta Co. Ltd., Osaka, Japan) in D-65 lighting, with standard angle of 2 degrees of shelter and 8 mm aperture of the measuring head. CIE L*a*b* color coordinates were given as mean values: L* (lightness), a* (redness) and b* (yellowness).

Sensory analysis
Sensory analyses were carried out in a sensory testing laboratory equipped with individual booths. Each booth was walled on three sides in order to prevent panelists influencing each other. All booths were provided with florescent lights to mask color differences between samples. Sensory tests were performed at room temperature (22-24°C). After a cooling period (4°C for 24 h), meat samples were cut to approximately 2.5×2.5×2.5 cm and labelled with random three-digit numbers. Meat samples were served in plastic bowls, in separate randomized order and individually to each of the 20 trained panelists. Panelists were selected according to ISO standard (ISO 8586, 2012(ISO 8586, , 2015. Overall acceptability was evaluated based on appearance, texture and aroma. For evaluation, a scoring range from one to five was used, with half and quarter points available. For each selected quality property, the coefficient of importance was determined in order to correct evaluations obtained by multiplication of means. The coefficients of importance were chosen according to the influence of specific properties on the overall quality (surface color -4, visually evaluated structure -3, palpatory evaluated firmness -3, and olfactory evaluated odor -10), and their sum was 20. By combining individual scores, a complex indicator was obtained that represented the overall sensory quality and was expressed as "percentage of the maximum possible quality" (maximum possible quality was 100%). By dividing this value with a set of coefficients of importance, a weighted average score was obtained, which also represented the total sensory quality of the meat from the three pig breeds. Total sensory quality scores were: 1.00 = very pronounced errors; 2.00 = clearly expressed mistakes; 3.00 = noticeable deviations; 4.00 = minor deviations and; 5.00 = fully meets the quality requirements.

Statistical analysis
Data were analyzed by descriptive and analytical statistical parameters, mean (M) and standard deviation (SD), using Graph Pad Prism 6.0. software (Graph Pad Software Inc., San Diego, CA, USA) and one-way analysis of variance (one-way ANOVA). The differences between means were compared by Tukey's post-hoc test. Levels of p<0.05 and p<0.01 were considered as significant and highly significant, respectively. The D'Agostino-Pearson normality test was used to verify the normal distribution of data. p>0.05 was considered as normal data distribution.

Results
Live weights and carcass weights after evisceration of wild boar, Landrace and Yorkshire pigs are presented in Table 2. There were significant differences among weights of the different pig breeds (p<0.05).
Chemical composition and pH of meat from wild boar, Landrace and Yorkshire pigs are presented in Table 3. Water content did not significantly  differ among the pig breeds (p>0.05). The contents of crude fat, crude ash and the pH differed significantly among the three pig breeds (p<0.05 and p<0.001), while protein content differed in Landrace and Yorkshire meat (p<0.01), but not compared to that of wild boar. The fat content was the lowest for wild boar and the highest for Landrace meat. The protein content of wild boar meat was significantly higher than that of Landrace meat (p<0.05), but did not differ from that of Yorkshire meat (p>0.05). The pH of Landrace and Yorkshire meat did not differ significantly, but was different to that of wild boar meat (p<0.05).
The volatile compounds in wild boar, Landrace and Yorkshire meat are presented in Table 6. There were significant differences among all determined volatile substances in meat from the three pig breeds (p<0.05). From the group of aldehydes, furfural and   Color parameters (L* a* b*) of wild boar, Landrace and Yorkshire pig meat are presented in Table 7. There were significant differences among all examined parameters in the CIE L*a*b* system that defined color.
In Table 8, sensory evaluation of individual sensory attributes, the percentage of the maximum score for all evaluated characteristics, and the weighted mean values of ratings are shown. The quality of wild boar, Landrace, and Yorkshire meat did not significantly differ in the main sensory characteristics (surface color, visually evaluated structure, palpatory evaluated firmness, and olfactory evaluated odor). Landrace meat achieved the highest numeric color score, followed by Yorkshire meat, which was slightly darker, and wild boar meat. The visually evaluated structure and palpatory evaluated firmness of Yorkshire meat (13.90 and 15.5, respectively), were the highest among the three pig breeds. Visual evaluations of Landrace (12.50) and wild boar meat (13.00) produced similar scores. The olfactory evaluated odor of meat from the three pig breeds showed that wild boar meat had the highest odor score (Table 8), followed by Landrace and Yorkshire meat. Overall sensory quality followed the order: Yorkshire (95.50%/ weighted average 4.77), Landrace (L) (92.00/4.60) and wild boar (90.50/4.52).

Discussion
The pigs' live weights were in line with breed characteristics (Furman et al., 2010), and the chemical composition of the meats were in line with our previous findings. In a study of meat quality characteristics of Duroc x Yorkshire, Duroc x Yorkshire x wild boar and wild boar meat, significant differences in meat chemical composition between breeds were observed (Ivanović et al., 2013). Václavková and Bečková (2007) examined the impact of different feed additives on chemical composition of M. longissimus dorsi in (Czech Large White x Czech Landrace) x (Hampshire x Pietrain). The fat content (2.1%) in the control pigs fed a basal diet was similar to our results for Yorkshire meat. However, the fat contents determined in the current study were not in line with the results of Šimek et al. (2004), who reported their pigs had 1.6% intramuscular fat. Choi et al. (2016) reported m. longissimus dorsi from Yorkshire pigs had a higher fat content than that from Landrace, which could be a consequence of differences in final weight and nutrition. In our study, proximate meat composition and pH varied significantly among the compared breeds. Similar results have been reported by other authors (Kosovac et al., 2009;Kasprzyk et al., 2015).
The ideal intramuscular fat content of fresh meat is between 2 and 3%, whereas meat with a fat content >3.5% can be rejected by consumers (Fernandez et al., 1999;Kasprzyk et al., 2015). In the current study, the fat content of Yorkshire meat was acceptable. However, Landrace meat had a higher fat content (3.83%) and wild boar meat had a lower fat content (1.76%), which could indicate the meat from these pigs was of low quality (Tyra and Zak, 2010;Kasprzyk et al., 2015). In spite of that, consumers nowadays prefer low fat and low cholesterol levels in food, and therefore, wild boar meat could be considered as favorable food for human consumption. Postolache et al. (2011) examined the chemical composition of m. longissimus dorsi from three-to four-year-old wild boar hunted in Romania. The proximate composition (water content of 75.36%, protein content of 21.81%, and fat content of 2.58%) and ultimate pH (5.56) of their boar meat differ from our current results. Those discrepancies could be a consequence of different ages and nutrition of the examined animals.
The most prevalent fatty acid was oleic acid in all examined breeds, followed by palmitic and stearic acid. The highest oleic acid content was determined in Yorkshire meat, followed by wild boar and Landrace meat. Regarding palmitic and stearic acid, wild boar meat contained the most, followed by Landrace and Yorkshire meat. The linoleic acid content was the highest in Landrace meat, and lowest in wild boar meat. Furthermore, there were significant differences between all determined fatty acids, which highlighted the impact of breed on fatty acid profile of meat, as others have said. Wood et al. (2004)  Furthermore, animals' diet can affect chemical composition, fatty acid profile and volatile compound content in meat (Wood et al., 2008;Čítek et al., 2015). The complete feed mixtures used in this study were the same for the two commercial breeds (Landrace and Yorkshire). Differences in fatty acid content between Landrace and Yorkshire meat occurred, regardless of the same diet being used. However, fatty acid content also differed between the pure breeds and wild boar meat. It should be noted that diet has an impact on meat quality, in conjunction with several different factors. Thus, diet (feed additives) can affect the fatty acid profile of meat, but does not have a crucial effect on intramuscular fat content (Čítek et al., 2015) ; Kouba et al., 2003;Okrouhla et al., 2013).
Among the saturated fatty acids, not all have the same effect on human health. It is considered that lauric (C12:0), myristic (C14:0) and palmitic (C16:0) acids can increase the concentration of cholesterol in plasma. Myristic acid had the most adverse effect, four times more pronounced than the effects of lauric and palmitic acids, on the cardiovascular system (Hegsted et al., 1959). Our pig meat contained only small amounts of myristic acid. Stearic acid, which was the most abundant saturated fatty acid in our study, is considered as neutral (Webb and O'Neill 2008;Kasprzyk et al., 2015).
Indicators of the nutritional value and health benefits of fat depend on the amounts of particular fatty acid groups. Regarding overall fatty acid contents, wild boar meat had the highest total saturated fatty acid content. The ratio of polyunsaturated to saturated fatty acids should be higher than 0.4 (Wood et al., 2008), and in our study, only wild boar meat did not fulfill this human health indicator.
Aldehydes are commonly found in the pig meat, as high as 50% (Xie et al., 2008;Lorenzo et al., 2013), or even 75% (Hou et al., 2018) of total volatile compounds. In contrast, in our study, aldehydes were not the most abundant volatiles, particularly in Landrace meat that contained just 2.45% aldehydes. Within the group, linear aldehydes are products of fat oxidative degradation, with the exception of phenylacetaldehyde, which is a product of amino acid degradation (Belitz and Grosch, 1987;Xie et al., 2008). Aldehydes, regardless of their amount, have a low aroma threshold and intensive and specific aroma, which can make them important contributors to meat's aromatic profile. Aldehydes, especially hexanal that is the most abundant and derived from linoleic and arachidonic acid, have grease, green grass, and apple flavors, (Yang et al., 2017;Hou et al., 2018). In our study, among the aldehydes, hexanal predominated in wild boar and Yorkshire meat, but it was not detected in Landrace meat. Aldehyde content is determined by fatty acid and protein content, and furthermore, is affected by several factors: chilling conditions, storage time, heat treatment of meat etc. Thus, the aldehyde content can vary significantly along with conditions of meat manipulation.
Ketones are considered to have a significant impact on meat aroma, especially when they occur in large amounts. Ketones have a specific aroma that is described as ether-like, buttery, spicy notes or blue cheese notes (Creuly et al., 1992;Lecanu et al., 2002). Furthermore, methyl ketones, and among them 3-Methyl-2(5H)-furanone that was the most abundant in our study, has buttery and creamy notes (Xie et al., 2008). Ketones can be produced by lipid oxidation as a consequence of autoxidation (Beliz and Grosch, 1987;Flores et al., 1997) or microbiological activity (Sunesen and Stahnke, 2003). For example, the β-oxidation activity of molds growing on the surface of dry-cured products results in 2-pentanone production. Ketones have high odor thresholds, and so we presume their contribution to the meats' total aroma profiles was significant, considering the large amount of ketones in the meats.
Heterocyclic compounds are significant odorants, and among them furan compounds, due to their low thresholds, might be major contributors to pig meat odor. Furan is derived from n-6 fatty acids, particularly linoleic acid (Elmore et al., 1999;Yang et al., 2017). These compounds were detected in various pig meat breeds (Zhao et al., 2017;Hou et al., 2018), and furan is described as having vegetable, green, earthy, and beany notes (Stetzer et al., 2008). In the current study, Yorkshire and Landrace meat contained more furan than did wild boar meat. Commercial breeds in our study received in their diets linoleic acid that is precursor for furan synthesis. Linoleic acid from pig diets will accumulate in muscles (Ramsay et al., 2001;Čítek et al., 2015;Pinelli-Saavedra et al., 2019), and thus affects the fatty acid and volatile profiles of meat.
On the contrary, 1-octen-3-ol that is generated from oxidative breakdown of linoleic acid was the highest in wild boar meat, despite this meat having the lowest content of linoleic acid. Considering that meat's volatile profile is multifactorial, we conclude that differences in nutrition have significant, but not decisive impacts. 1-octen-3-ol is considered to have sweet, earthy odor (Hong et al., 1988). Furthermore, alcohols are products of lipid oxidation or reduction of aldehydes to alcohols (Lorenzo et al., 2013). They have herbaceous, woody and fatty perception and contribute to flavor and odor meat profile due to their low thresholds (Lorenzo et al., 2013).
Meat's volatile compounds and flavor profile are affected by numerous factors. Volatiles can be derived thermally from fatty and amino acid degradation, so the volatile profile depends on the thermal processes applied (cooking, smoking, roasting). In our study, spices that can significantly contribute to meat flavor development, were not used, which could explain disagreements with other studies (Xie et al., 2008;Lorenzo et al., 2013).
Meat color correlates with myoglobin content, but also is closely related to intramuscular fat content and pH (Lee and Joo, 1999;Mancini and Hunt, 2005;Choi et al., 2016). In our study, Landrace meat had the fat highest content, which logically explains Landrace meat's lightness values. However, wild boar meat had the lowest pH, which could be expected to result in high lightness values, but this was not the case in our study. Wild boar meat had higher a* and b* values than did Landrace and Yorkshire meat, which could be a consequence of the higher myoglobin content in game meat. Marchiori and de Felício (2003) instrumentally measured pig meat color (at 24 h post-slaughter in m. longissimus dorsi). Their L* and b* values were higher than ours, but their a* values were lower than ours. Meat color, measured after seven days in m. longissimus lumbrorum from Large White Landrace (Lebret and Guillard, 2005), was darker than our Yorkshire meat but lighter than our Landrace meat. Marchiori and de Felício (2003) also measured the color of wild boar meat (48 h post-slaughter in m. longissimus dorsi); their L* and b* values were higher than ours.
The visually evaluated structure of Yorkshire meat indicated this meat had uniform distribution of muscle fibers at the intersection. It is difficult to compare the results of sensory analysis between different authors and between different techniques. Kasprzyk et al., (2010) evaluated Pulawska meat, wild boar and Pulawska x (Hampshire x Wild boar). In that study, wild boar meat received the lowest rating, while cross-breed meat achieved a perfect score. Morrison et al. (2007) investigated the effect of different housing methods on sensory qualities. The scores varied slightly, but did not differ in tenderness, juiciness, pork flavor or overall desirability of pork produced from the two housing treatments. These results (Morrison et al., 2007) are similar to ours. Although we did find slight differences in the sensory evaluation of meat appearance, they did not affect the acceptability of meat.

Conclusions
Unsaturated fatty acids accounted for 57.20% of total fatty acids in wild boar meat, 59.51% in Landrace meat and 66.74% in Yorkshire meat. Yorkshire meat had the most favorable unsaturated to saturated fatty acid ratio and the highest nutritional value. On the other hand, wild boar meat had the lowest intramuscular fat content. Regarding overall sensory acceptability, Yorkshire meat achieved the highest score, followed by Landrace and wild boar meat. In conclusion, sensory evaluation and indicators of the nutritional value showed that meat from pure breeds, in particularly Yorkshire, has benefits for consumers, but wild boar meat will satisfy consumers' expectations for lean meat.
The present study is not without limitations. Indeed, some fatty acids and volatile compounds were not identified, indicating that further research is required. Furthermore, evaluation of pork meat quality was conducted, but the study did not include the quality of meat products. Finally, other pig breeds are likely to have other characteristics, so they deserve study.

Disclosure statement:
No potential conflict of interest was reported by authors.