Study of meat quality and flavour in different cuts of Duroc‐Bamei binary hybrid pigs

Abstract Background Meat quality and flavour are important criteria for judging fresh pork and processed products. However, there have been few studies on meat quality and volatile flavour substances of different parts of binary hybrid pigs. Objective To study the differences in meat quality and volatile flavour substances between different cuts of pork, which could provide the basis for consumer decision‐making when purchasing pork. Methods Twenty Du‐Ba binary hybrid pigs (first filial [F1] generation) bred from Duroc and Bamei pigs were used. This study systematically compared and analysed the basic nutritional components, amino acid composition, fatty acid composition and flavour profiles of longissimus dorsi, rib muscle and tendon meat of four Du‐Ba binary hybrid pigs; all assays were repeated in triplicate. Results Crude protein, calcium and phosphorus content in tendon meat were higher than that in the longissimus dorsi. The intramuscular fat content of the rib muscle was higher than that in the longissimus dorsi and tendon meat (p < 0.05). The amino acid content was highest in the tendon meat. The levels of essential amino acids and flavour‐associated amino acids per kilogram of longissimus dorsi were higher than those in the rib muscle and tendon meat. Moreover, the content of aspartic acid, serine and cystine were higher in the longissimus dorsi than in the other two parts. The type of saturated fatty acids and the type and content of unsaturated fatty acids in tendon meat were higher than in the longissimus dorsi and rib muscle. The total content of volatile flavour compounds was higher in the longissimus dorsi than in the rib muscle and tendon meat. Conclusion The rib muscle contains high deposits of fat, and tendon meat has a relatively high nutritional value, while the longissimus dorsi has a stronger flavour.


| INTRODUC TI ON
China is the largest pig-raising country in the world. Pork consumption accounts for more than 60% of the total meat consumption in China (Carvalho-Salemi et al., 2017). According to the Organization for Economic Development (OECD) and the United Nations Food and Agriculture Organization (FAO) analysis, pork consumption in China will reach 59.3 million tons by 2020 (Hu et al., 2015). The flavour of pork is enhanced by its soft muscle fibres and low levels of connective tissue; these properties have caused it to be favoured by a vast number of consumers (Vlachos et al., 2016). In addition, pork has a high total content of all amino acids (Wolk, 2017). Pork is rich in potassium, iron, magnesium, and other elements (Benet et al., 2015).
The B vitamins, especially vitamin B1, are highly abundant in pork (Esteve et al., 2002). Fat is the main nutritional component of pork; this macronutrient is necessary to maintain nutritional balance and enhance the anti-disease immune function of the human body (Kucha et al., 2018).
Pork quality is primarily determined by the edible and nutritional quality of the meat, which can differ depending on the cut of pork (Alfaia et al., 2019). Pork flavour is mainly composed of water-soluble and volatile compounds (Wojtasik-Kalinowska et al., 2016). Meat quality and flavour are important criteria when judging fresh pork and processed products. Both domestic and foreign studies have shown that meat quality indicators differ depending on the cut of pork, and these indicators have become the basis for consumers to select pork (Long et al., 2017;Rosenvold & Andersen, 2003). Xi et al. researched the difference in content of flavour-providing substances in different muscle parts of Bamei pigs, and the results suggested that compared with pork belly, the longissimus dorsi had a lower fat, higher protein, and higher amino acid content, which is more in line with people's demand for high nutritional meat (Xi et al., 2019). Xu et al. tested the meat quality parameters of different carcass parts of ten 100 kg Duroc gilts, and the results indicated that the cut of the pork had a significant effect on some meat quality parameters; compared to the muscles of the ham, the muscles around the shoulder had lower drip loss, muscle fibre diameter, shearing force, and intramuscular fat (Xu et al., 2004).
Studies on pork quality and volatile flavour substances are mostly based on the differences between different breeds or different treatment methods (Lanferdini et al., 2018;Lebret et al., 2018).
However, there are few studies on pork quality and volatile flavour substances of different parts of binary hybrid pigs. In this experiment, Du-Ba binary hybrid pigs were bred from Duroc and Bamei parent pigs using the binary hybrid model (Duroc × Bamei pig).
During the feeding period, pigs were fed with high-quality feed to obtain commercial and ecological high-quality pork. In order to study the differences in meat quality and volatile flavour substances between different parts of the pig, three different cuts of pork (longissimus dorsi, rib muscle, and tendon meat) were selected to provide a reference for the breeding of high-quality pork breeds and the basis for consumers to purchase pork that meets their demands.

| Slaughtering of pigs and subsequent muscle sampling
Pigs were fattened until 240 days (115 ± 5 kg), at the completion of the feeding trial, all pigs were subjected to overnight fasting with no access to water for 2 hr. To determine meat quality and flavour substances, four pigs with identical growth, with good health and nutrition were randomly selected for slaughter. Within 2 hr after slaughter, longissimus dorsi (Tenderloin), rib meat and tendon meat samples were taken from each pig according to the technical specifications of the NY/T821-2004 pig muscle quality determination, and samples were stored in marked self-sealed bags and were then vacuum-packed. Routine nutrients and volatile flavour compounds of fresh meat were determined at the College of Animal Science and Technology of Gansu Agricultural University and Qingdao Kechuang Quality Testing Co., Ltd., respectively. All assays were repeated in triplicate.

| Determination of basic nutritional components
The crude protein content was determined using the semi-micro Kjeldahl method (GB 5009.5-2010). The fat content was determined using the Soxhlet extraction method (GB/T 5009.6-2003). Protocols for the determination of protein (GB 5009.5-2010)

| Determination of amino acid content and amino acid score
The amino acid content was determined using the determination method of amino acids in food (GB/T 5009.124-2003). The tryptophan content was determined using the colorimetric method after alkaline hydrolysis of each sample. All measurements were repeated in triplicate.
Amino acid score (AAS) = the content of amino acid per gram nitrogen (or protein) of the tested protein/the content of amino acid per gram nitrogen (or protein) in the ideal model × 100.  ( The energy and amino acid data were calculated theoretically, and others were measured value (in bold).

| Determination of fatty acids content
The meat samples were pretreated according to the GB/T 17376-2008.
The fatty acid content was determined according to Wang et al. (2016).

| Determination of flavour substances
2.4.1 | Determination of nucleotide and inosine monophosphate content Nucleotide determination was performed according to the national food safety standard (the determination of nucleotides in infant food and dairy products). The content of inosine monophosphate (IMP) in different parts of fattening pigs was determined by high-performance liquid chromatography (Wu et al., 2005).

| Determination of flavour substances
The volatile flavour substances in the meat samples were analysed by Qingdao Kechuang Quality Testing Co., Ltd. The volatile substances in fresh meat samples were pretreated with solid-phase microextraction (SPME), and subsequently separated and identified by gas chromatography-mass spectrometry (GC-MS).
Sample processing method: First, 5 ml of meat sample was added to a 20 ml headspace bottle (to avoid exceeding 1/4 of the headspace bottle), and a tightened bottle cap was placed in the bottle.
The headspace bottle was subsequently placed in the headspace at 55°C for 15 min. Lastly, the sample was extracted for 20 min by using the SPME needle with manual injection, and the extraction needle remained for 5 min at the injection port ; SPME needle was aged at 250°C for 10 min before use. After cooling to room temperature, the SPME needle was washed with methanol, ethanol, ether, n-hexane, deionized water, and methanol in turn).
Gas phase conditions: The TG-5MS capillary column (30 m × 0.25 mm × 0.25 µm) was used as the chromatographic column. Helium gas was used as the carrier, and the flow rate was 1 ml/ min, with no shunt. The injection temperature was 240°C and the column box temperature was 50°C. Temperature rising procedure: The initial temperature was maintained at 50°C for 2 min, and the temperature was increased to 240°C for 5 min at a heating rate of 4°C/min (Chen, 2004).

| Statistical analysis
Excel 2010 was used for data collection. The data are represented as mean ± standard deviation. Data were analysed using one-way analysis of variance and Duncan testing using the SPSS 17.0 software, with p values < 0.05 considered to be statistically significant.
All assays were repeated in triplicate.

| Basic nutritional components
According to Table 2, all indicators were within the normal range.
The content of crude protein, calcium, and phosphorus in tendon meat was higher than in longissimus dorsi, among which the phosphorus content was significantly different (p < 0.05). The intramuscular fat content of the rib muscle was higher than that in the longissimus dorsi and tendon meat (p < 0.05).

| Amino acid content
The amino acid contents of different parts of the Du-Ba binary hybrid pigs are presented in Table 3. A total of 17 amino acids were quantified in longissimus dorsi, rib muscle and tendon meat of Du-Ba binary hybrid pigs, and no tryptophan was detected in any samples.
The amino acid content of tendon meat was the highest. The proportion of essential amino acids and flavour-associated amino acids in total amino acids per kilogram of longissimus dorsi were higher than those of the other two cuts. The proportion of glutamate in the total amino acids per kilogram of rib muscle was higher than that in the other two parts.
In the four non-essential amino acids, the differences in the alanine content of the three parts were not significant (p > 0.05), and the content of aspartic acid and serine in the longissimus dorsi were higher than in the other two cuts. The cystine content in the longissimus dorsi was significantly higher than in the rib muscle and tendon meat (p < 0.05). According to the FAO/World Health Organization (WHO) model standard, EAA/TAA (essential amino acids/total amino acids) should be approximately 40% in the better protein composition. The EAA/TAA in the longissimus dorsi of Du-Ba binary hybrid pigs was 44.08%, which is an ideal protein model. Table 4, compared with the content of the essential amino acids in ideal protein proposed by FAO/WHO, the essential amino acids in longissimus dorsi, rib muscle, and tendon meat were lower than those in the ideal model, while the threonine and lysine contents approached the ideal model.

As shown in
The lysine score of the longissimus dorsi approached the ideal model.

| Fatty acid composition
As illustrated in Table 5, the longissimus dorsi and rib muscles of the Du-Ba binary hybrid pig included 15 saturated fatty acids and six unsaturated fatty acids. The tendon meat included 16 saturated fatty acids and seven unsaturated fatty acids. There were differences in the content of saturated and unsaturated fatty acids in the three parts (p < 0.05). The cholesterol content of the longissimus dorsi muscle was significantly higher than that of the rib muscle (p < 0.05). There was no significant difference between the cholesterol content of the longissimus dorsi and tendon meat (p > 0.05). Note: " 1 " was flavour amino acid; " a,b,c " indicate a significant difference (p < 0.05).

TA B L E 3
The amino acid content in different parts of Du-Ba binary hybrid pig muscle (g/kg)

| Flavour substances
As shown in Tables 7 and 8

| D ISCUSS I ON
Pork is one of the most consumed types of red meat in many countries worldwide. This study aimed to explore the differences in meat quality and volatile flavour substances between different cuts of pork, the results of which could provide the basis of consumer decisions when purchasing pork.
Pork has many advantages as a food product; high levels of protein and fat can provide nutrition and energy for the human body  of the Hezuo pig were C16 and C18 fatty acids , which was consistent with the results of this study for the Du-Ba binary hybrid pig. In addition, the intramuscular fat content of the rib muscle is higher than that of the longissimus dorsi and tendon meat. Xu et al. showed that the muscles around the shoulder of Duroc gilts have lower drip loss, muscle fibre diameter, shearing force, and higher intramuscular fat when compared with other cuts (Xu et al., 2004). However, a review of the literature has demonstrated that there are few studies on the differences in meat quality between different parts of pork. Thus, this study illustrates that the rib muscle has high levels of fat deposits, and tendon meat has a relatively high nutritional value.

Rib muscle
Meat flavour is generally described as 'umami;' this flavour comes from the meat components, including free amino acids, small peptides, IMP and sugar (Yang et al., 2010). After livestock slaughtering, adenosine triphosphate (ATP) in muscle degrades continuously, and IMP is produced. IMP and other decomposition products in meat accumulated continuously, which made the meat taste thicker (Kitada et al., 1983). Xi et al. illustrated that the IMP content in the longissimus dorsi was higher than that in the rib muscle of the Bamei pig (Xi et al., 2019), and the IMP content was also higher than that in the rib muscle of the Du-Ba binary hybrid pig.
Hydrocarbons mainly refer to alkanes and olefins, which can be oxidized and gradually decomposed to produce aldehydes, ketones, and a small amount of esters; these improve the overall flavour of meat products (Al-Thaiban et al., 2018). The difference in the relative content of aldehydes, alcohols and ketones is the most important reason for the difference in pork flavour (Pan et al., 2012).
One previous study showed that the content of volatile flavour compounds (including aldehydes, alcohols, ketones) in the longissimus dorsi was higher than that of the rib muscle and tendon meat in PIC swine (Guo, 2009), which was consistent with the results of the Du-Ba binary hybrid pig. Among the aldehydes, 2,4-decadienal, which has a fat aroma, comprises a unique component of pork aroma (Sucan et al., 2002). Among the alcohols, 1-Octen-3-ol has the flavour of ripe mushrooms, which contributes greatly to the flavour of pork (Kim & Kim, 2005 other parts of ZFY pigs , which is consistent with the results of this study. Therefore, the findings indicate that the longissimus dorsi has a stronger flavour.

| CON CLUS ION
In conclusion, the rib muscle contains the largest fat deposits, the tendon meat has a relatively high nutritional value, while the longissimus dorsi has a stronger flavour. This study will provide a reference for breeding high-quality pork breeds and the basis for consumers to purchase pork to meet consumer demand. However, this study has several limitations. First, this study used only a small number of experimental subjects owing to the influence of feeding cost, market price and other factors, which may affect the reliability of the results, and more studies are needed to verify this. Second, the limitation of the experimental conditions, such as extraction temperature, might affect the experimental results. Third, it is not sufficient to study the meat quality and flavour substances in longissimus dorsi, rib muscle and tendon meat; it will also be necessary to research other parts of the Du-Ba binary hybrid pig.

CO N FLI C T O F I NTE R E S T
The authors declare that they have no conflicts of interest.

E TH I C S S TATEM ENT
The animal procedures used in this study were reviewed and ap-

PEER R E V I E W
The peer review history for this article is available at https://publo ns.com/publo n/10.1002/vms3.409.