Comparative analysis of meat sensory quality, antioxidant status, growth hormone and orexin between Anqingliubai and Yorkshire pigs

ABSTRACT The pig breeds play an important role in post-mortem meat sensory quality. The aim of this study was to analyse the differences of meat sensory quality, antioxidative ability, growth hormone and orexin between Anqingliubai and Yorkshire pigs. Six Anqingliubai and Six Yorkshire pigs (approximately 100 kg ± 1.5 kg) were slaughtered to assess the longissimus dorsi meat sensory quality, antioxidant ability, serum growth hormone and orexin. Results showed that the Anqingliubai pigs exhibited higher pH, a* and intramuscular fat, but lower L* and cooking loss in longissimus dorsi compared with the Yorkshire pigs (P < 0.05). The malondialdehyde level in the longissimus dorsi muscle of the Anqingliubai pigs was lower than that of Yorkshire pigs. Compared with the Yorkshire pigs, the Anqingliubai pigs exhibited higher superoxide dismutase, catalase and total antioxidant capacity in longissimus dorsi muscle (P < 0.05). Meanwhile, the Anqingliubai pigs showed lower serum growth hormone, but higher serum orexin compared with the Yorkshire pigs (P < 0.05). The different meat sensory quality between two pig breeds may be partly caused by different muscle antioxidant ability, intramuscular fat, serum GH and orexin level.


Introduction
With the rapid development of the global economy, consumers' demands for meat products have gradually changed from the requirements of quantity and basic safety to the requirements of meat quality, such as tenderness, colour, flavour, etc. (Zeng et al. 2016). The breeding direction of pig was higher growth performance and percentage of lean meat for a long time. However, this breeding method leads to a sharp decline in meat sensory quality (Kanis et al. 2005).
The meat sensory quality was affected by various factors, especially pig breeds (Te Pas et al. 2017;Zhang et al. 2015a;Muhlisin et al. 2014). Franco et al. (2014) and Ruusunen et al. (2012) reported that different pig breeds obviously showed different meat sensory quality. Western lean pig breeds have been intensively selected for higher body weight gain, feed efficiency, and lean meat percentage, which may have negative impacts on the meat sensory quality (Guo et al. 2011;Miao et al. 2009). For contrary breeding direction, Chinese local lard-pig breeds exhibit different meat sensory quality including pH, flavor, texture, and storage quality (Suzuki et al. 1991;Li et al. 2008;Liu et al. 2017). These differences in the meat sensory quality may be caused by intramuscular fat (IMF), which have a positive effect on the meat sensory quality of pig (Zhang et al. 2015b;Fernandez et al. 1999).
Anqingliubai pig is one of the most famous obese breeds which have the characteristics of early sexual maturity and good anti-stress ability (Zhang et al. 2015a). Yorkshire pig is an excellent lean pig breed in the world . It exhibits fast growth rate, good feed conversion efficiency, and high lean meat rate. There were many works reported the differences between the Chinese local lard and Western lean pig breeds. However, few studies investigate the differences in meat sensory quality, oxidation state, growth hormone (GH) and orexin secretion between Anqingliubai and Yorkshire pigs. Consequently, the aims of the present work were to quantify and compare the meat sensory quality, lipid oxidation, major antioxidant, GH and orexin levels between Anqingliubai and Yorkshire pigs, which could provide useful information to further understand the possible mechanisms of differences in lean and lard pigs.

Animals and sample collection
The animal experimental work was approved by the Animal Care and Ethics Committee of Anhui Agricultural University (Permit number: SYXK 2016-007). Six Anqingliubai pigs and six Yorkshire pigs were used in this experiment. The pig diet was based on the corn-soybean meal and formulated according to National Research Council (NRC 2012). These pigs were fed ad libitum and housed in the cooperative farm of college of animal science and technology at Anhui Agricultural University. Due to the Anqingliubai and Yorkshire pigs being slaughtered at 100 kg in the market, the animal experiment lasted for 10 month for the Anqingliubai pigs and 6 month for the Yorkshire pigs according to similar slaughter weight (100 kg ± 1.5 kg). After fasting overnight, 12 pigs were slaughter for sampling. And then, the longissimus dorsi muscles and blood were collected and stored at 4°C and −80°C, respectively, for meat quality and chemical analysis.

Determination of meat sensory quality
The colour (lightness: L*, redness: a*, yellowness: b*) of meat was measured 24 h post mortem (4°C preservation) from an average of values using a chromameter (Konica Minolta Chroma Meter CR-300, Japan). The meat pH was measured at the centre of the longissimus dorsi sample by pH instrument (Mettler-Toledo, Switzerland). The meat sample was suspended in an inflated plastic bag for 24 h at 4°C. Then this sample was reweighed, and the drip loss (DL) was calculated as a percentage of the initial weight. The cooking loss (CL) was measured as follows: meat sample was placed in steam for 30 min, and the CL was calculated as a percentage of the initial weight. IMF was detected using Association of Official Analytical Chem-ists (1997) methods as described (Fortin et al. 2005).

Determination of malondialdehyde (MDA)
A 0.5 g longissimus dorsi muscle was homogenized in a glass homogenizer with 4.5 ml of ice physiological saline (0.9% NaCl), and then the homogenate was centrifuged at 3500 rpm for 10 min (4°C) in refrigerated centrifuge (Eppendorf, Germany). The supernatant was stored at −80°C. The MDA assay kits (Jiancheng company, Nanjing, Jiangsu province, China; http://www.njjcbio.com/) was used to detected MDA content according to the manufacturer's instructions.

Determination of serum GH and orexin levels
As the Li et al. (2012) described, the serum GH and orexin levels were detected by GH and orexin ELISA kits (ruicong mlbio company, Shanghai, China) according to the manufacturer's instructions.

Statistical analysis
Statistical analysis was performed by SPSS 18.0 for Windows statistical software package (SPSS, USA). Every pig was regard as an experimental unit. The t-test was used to compare two groups, and P < 0.05 was considered as significance. The value expressed as means with a SEM.

Meat sensory quality
The results of meat quality were shown in Table 1. Compared with the Yorkshire pigs, the Anqingliubai pigs showed higher pH and a* values, but lower L* and CL values (P < 0.05). Furthermore, the IMF was higher in the Anqingliubai pigs than that in the Yorkshire pigs. There were no significant differences in DL and b* values between Yorkshire and Anqingliubai pigs (P > 0.05).

MDA concentration
The MDA concentration of Longissimus dorsi muscle in Yorkshire and Anqingliubai pigs was shown in Figure 1. Compared with the Yorkshire pigs, the Anqingliubai pig exhibited lower MDA concentration (P < 0.05).

Antioxidant activities
The antioxidant activities of longissimus dorsi muscle in Yorkshire and Anqingliubai pigs were shown in Figure 2. Compared with the Yorkshire pigs, the Anqingliubai pigs exhibited higher SOD, CAT and T-AOC activities (P < 0.05). However, there were no significant differences in GSH and GSHPx activities between two breeds (P > 0.05).

Serum GH and orexin levels
The serum GH and orexin levels in Yorkshire and Anqingliubai pigs were shown in Figure 3. Compared with the Yorkshire pig, the Anqingliubai pigs exhibited lower serum GH, but higher serum orexin levels (P < 0.05).

Discussion
Pig breed is one of the main factors affecting pork sensory quality (Pugliese and Sirtori 2012;Kouba and Sellier 2011;Zheng et al. 2018). Generally, the obese-pig and lean-pig breeds showed different meat sensory quality (Guo et al. 2011;Miao et al. 2009;Liu et al. 2017). Shen et al. (2014) reported Chinese Tibetan pig and Liang-Shan pig have higher IMF, pH 45min , pH 24h , pH 48h and pH 72h , but lower DL 24h and DL 48h than DLY pig, and there was a significant effect of breed among three breeds. Zhang et al. (2015b) suggested that Chinese rongchang pig exhibited greater IMF, pH 45min , pH 24h compared with the Landrace pig. Chen et al. (2018) reported that Chinese local pig breeds (laiwu pig, Lulai pig, Wulian pig, Yantaipig and Yimeng pig) have better meat colour than commercial crossbreed pig DLY. Similar results of meat sensory quality were also found in the Anqingliubai and the Yorkshire pigs, which suggested that the Anqiuliubai pigs had greater meat sensory quality than that in the Yorkshire pigs. Furthermore, the Jinhua pig (Guo et al. 2011;Miao et al. 2009), Meishan pig (Suzuki et al. 1991), Taihu pig (Li et al. 2008), and Min pig  showed better meat sensory quality compared with the Landrace pig, Duroc × Landrace pig, Landrace pig, and Yorkshire pig, respectively. It has been demonstrated that lipid oxidation affected the sensory quality in the post-slaughter meat of pig (Chen et al. 2018). MDA is one of the important circulating indicators which reflect the degree of lipid oxidation in muscle (Lykkesfeldt and Svendsen 2007;Del Rio et al. 2005). Chen et al. (2012) reported that the MDA content of longissimus dorsi muscle was lower in the Laiwu pigs (Chinese obese pig) than in the Yorkshire pigs after slaughter. Similarly, the Anqingliubai pigs exhibited lower muscle MDA content compared with the Yorkshire pigs, suggesting that the longissimus dorsi muscle of Anqingliubai pig had lower level of lipid oxidation in the present experiment.
The oxidative degree of post-slaughter muscle which influences the meat sensory quality is retarded by the action of anti-oxidative Chen et al. 2018). The antioxidant system included a non-enzyme system (GSH, V E , polyphenol, etc.) and endogenous antioxidative enzymes (SOD, CAT, GSHPx, etc.). GSH, SOD, CAT and GSHPx play an important role in the protection of meat quality Cheng et al. 2017). Some studies have shown that the post-slaughter muscle antioxidant system can decrease the concentrations of free radicals to inhibit the oxidation of polyunsaturated fatty acids, thus affecting the shelf-life of pork and maintaining the meat quality (Chen et al. 2018). Hernández et al. (2004) and Chen et al. (2018) suggested that the different breeds showed the different anti-oxidative capacity in the muscle. The SOD, CAT and T-AOC activates in Anqingliubai pigs were statistically significant higher than in the Yorkshire pigs. These results indicated that Anqingliubai pork meat have higher resistance to oxidative stress post-mortem.
IMF is one of the important factors affecting meat sensory quality such as flavor, meat colour, fibre type, tenderness and juiciness (Fernandez et al. 1999;Zhao et al. 2009). Generally, a decreased level of (IMF) has a negative influence on the meat sensory quality of pig (Zhao et al. 2009). It is well known that IMF content depends on fat metabolism including lipogenesis, lipolysis, exogenous fatty acid uptake, and fatty acid oxidation (Wood et al. 2008;Zhang et al. 2015b). GH (a peptide hormone) promoted the muscle growth and correlated negatively with lipogenesis (Cordoba-Chacon et al. 2015). However, orexin regulated food intake and correlated positively with lipid accumulation (Wojciechowicz et al. 2016). Therefore, the serum GH and orexin concentrations could partly explain the different IMF content between pig breeds. Oksbjerg et al. (1995) and Parr et al. (2016) reported that injection of porcine GH could markedly decrease pork IMF of longissimus dorsi muscle. Li et al. (2012) suggested that the Chinese Rongchang pig showed lower serum GH, but higher serum orexin levels than the Landrace pig. In the present study, Anqinliubai pig exhibited higher IMF concentrations than the Yorkshire pig, which is consistent with its lower serum GH and higher serum orexin levels.

Conclusions
In conclusions, the longissimus dorsi meat sensory quality of Chinese Anqingliubai pig is different from the Yorkshire pig. Compared with the Yorkshire pig, the Anqingliubai pig showed the higher muscle antioxidant ability and serum orexin level, but lower muscle MDA and serum GH level. The different meat sensory quality between two pig breeds may be partly caused by different muscle antioxidant ability, serum GH and orexin level. The present findings may provide valuable information for understanding the differences in meat quality between Anqingliubai and Yorkshire breeds.

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