Research Article

Pork Quality Improvement Through Dietary Supplementation of Ingredients Enriched with Unsaturated Fatty Acid and Natural Antioxidants: New Research Trend

Hai Thanh Nguyen1*, Cuong Kien Nguyen2, Duy Ba Ngo2, Anh Thi Ngoc Dang1*

1Department of Animal Production, Faculty of Animal Science and Veterinary Medicine, Nong Lam University, Ho Chi Minh City, Vietnam;2Department of Veterinary Biosciences, Faculty of Animal Science and Veterinary Medicine, Nong Lam University, Ho Chi Minh City, Vietnam.

Received | April 16, 2024; Accepted | June 15, 2024; Published | August 06, 2024

*Correspondence | Anh Thi Ngoc Dang and Hai Thanh Nguyen, Department of Animal Production, Faculty of Animal Science and Veterinary Medicine, Nong Lam University, Ho Chi Minh City, Vietnam; Email: [email protected], [email protected]

Citation | Nguyen HT, Nguyen CK, Ngo DB, Dang ATN (2024). Pork quality improvement through dietary supplementation of ingredients enriched with unsaturated fatty acid and natural antioxidants: new research trend. Adv. Anim. Vet. Sci. 12(9): 1716-1730.

DOI | https://dx.doi.org/10.17582/journal.aavs/2024/12.9.1716.1730

ISSN (Online) | 2307-8316; ISSN (Print) | 2309-3331

Copyright: 2024 by the authors. Licensee ResearchersLinks Ltd, England, UK.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

INTRODUCTION

Pork is the most commonly consumed meat worldwide (UDSA, 2023) due to its necessary nutritional values (Petroski and Minich, 2020) and inclusion of no anti-nutrients (Zequan et al., 2021). In particular, pork consumption accounts for the largest proportion of the total meat with 36% every year, followed by the meat from poultry and cattle at 33% and 24%, respectively (UDSA, 2023). Currently, the meat quality of pigs is significantly affected by a wide range of potential elements such as raising protocols, daily feeding and diet, slaughtering procedures, or processing methods. Nutrients, tenderness, juiciness, and unique flavors in pork are important factors in determining meat quality. According to the Irish customer’s standpoint, tenderness was the most important factor, followed by taste and juiciness (O’Mahony, 1991), while both Danmark and Belgian citizens have expected unique odors in pork (Bryhni et al., 2002; Verbeke and Viaene, 1999). Meat with high-fat compounds can decrease palatability due to unacceptable odors (Soldatova and Korzunov, 2022) during long-term storage (Buckley et al., 1989; Sohaib et al., 2017). The production and supply of fresh, nutritional, safe, and high-quality meat for human beings will be an urgently important strategy for the pork industry and other meat sources in the near future (Sofos, 2008).

On the other hand, it has been concerned the high consumption of saturated fatty acids (SFA) in pork seems to be unhealthy for humans since some negative impacts derived from SFA on the circulatory system have been recognized (Mozaffarian et al., 2009). It has been demonstrated the more these fatty acids are absorbed, the greater the risk of cardiovascular diseases (Zong et al., 2016). Recently, there has been interested in the addition of nutritional components into daily diets in order to increase the accumulation of unsaturated fatty acid (UFA) accompanied by decreasing that of SFA in muscle (Navarro et al., 2021). A series of reactions can be started occurring both inside and outside of pork by different pathways such as chemical, biological and physical (temperature, light) ones or bacterial contamination in post-slaughter (Lawrie RA, 1968). Bacterial contamination in post-slaughter meat processing is a significant concern addressed in various research papers. Previous studies have shown that microbial contamination of fresh meat occurs during different stages of processing, including slaughter, carcass dressing, and chilling (Aiyegoro, 2014). Besides, it has been indicated lipid oxidation has a positive effect on meat quality rather than other reactions happening in tissue. UFA has one or some double bonds in the chemical structure which is not as durable and more prone to oxidation, thus UFA is the precursor component for synthetic flavor compounds throughout the period of rigor mortis (Fan, 2021), but there seems to be an appearance of rancidity in the post-rigor stage by the excessive or uncontrolled oxidation (Nawar, 1969; Soldatova and Korzunov, 2022).

It has been showed the inclusion of linseed in the daily diet for pigs could have a feasible solution for improving nutritional components (Wang et al., 2021), such as the increase of Omega-3 PUFA in tissue (Dugan et al., 2015; Huang et al., 2020; Yi et al., 2023). The dietary supplementation of macadamia oil also had the positive effect on meat quality (Junior et al., 2022; Navarro et al., 2021). However, the potential main disadvantage of the high unsaturated fatty acid content in pork has been associated with the state of lipid oxidation (Domínguez et al., 2019). Furthermore, alpha-tocopherol is recognized as an effective antioxidant (Jensen et al., 2010), supporting to neutralize free radicals during post-mortem storage after slaughter (Li and Liu, 2012). It has been recommended a sufficient level of 100 mg alpha-tocopheryl acetate is needed for daily requirment of meat pigs to ensure meat quality and oxidative stability of pork (Jensen et al., 2010). The combinative supplemenation of linseed oil and alpha-tocopherol significantly modifies the ratio of n-6/n-3 fatty acids (Hoz et al., 2003). Several previous studies have reported that phytogenic compounds, such as phenolic compounds and essential oils (Puvača et al., 2013), can potentially improve the subtable oxidation in pork. Phenolic acid is noticed to have the ability to reject free radicals and protect membranes (lipoproteins) (Kiokias et al., 2020). In addition, phytogenic bioactive compounds can induce significant changes of the profile of fatty acids due to the deposition of IMF in pork loin (Yang and Zhang, 2015). The addition of herbal mixture into the daily diet at 2% on dry matter intake (DMI) improved the ratio of n-6 and n-3 PUFA in the pork (Paschma and Wawrzyński, 2007). However, the definitive conclusion of effect of the dietary addition of ingredients with high UFA and natural antioxidants in pig industry has not been obtained yet due to inconsistent previous results, as well as there is no comprehensively systematic overview of all existing findings on this issue. It should be required to comprehensively identify and discuss the possible aspects related to the changes in meat quality through the supplementation of ingredients with high UFA and natural antioxidants into daily diet for pigs. Furthermore, a better understanding of the underlying mechanisms of meat quality changes under the potential supplementation of ingredients with high UFA and natural antioxidants can provide further insights.

In the present systematic review, therefore, we comprehensively discuss all aspects and mechanisms of pork quality changes through dietary supplementation of ingredients enriched with unsaturated fatty acid and natural antioxidants.

The main chemical composition of pork

Protein in pork loin is generally recognized as a source of high biological value (Hoagland, 1945) and its content with stable levels (21-23.3%) in Longissimus dorsi (LD) muscles (Table 1). Furthermore, it contains a variety of essential amino acids (Wu et al., 2014) in sufficient quantity and proportion to meet nutritional requirements for humans (Ma et al., 2020) such as Lysine (8.1%) or Methionine (2.3%) (Greenhut et al., 1948). Evaluation of the

 

Table 1: Chemical compounds of Longissimus dorsi (LD) muscles.

Protein (g)	Fat (g)	Ash (g)	Ca (mg)	P (mg)	Fe (mg)	Reference
21.95	6.92	0.97	7.00	226	-	UDSA, 2022
23.30	3.20	1.12	6.00	370	-	NUTTAB, 2021
23.23	4.40	1.37	-	-	-	Anh et al., 2019
22.10	3.01	1.20	5.00	210	-	Chen et al., 2019
19.10	1.51	-	5.78	175.40	1.29	Tóth et al., 2009
22.31	3.16	-	11.00	-	5.01	Ren guang-zhi et al., 2008

 

Table 2: Fatty acid profiles of Longissimus dorsi muscle after slaughter in some countries.

Items	Vietnam1	Australia2	China3	Brazil4
Myristic acid (C14:0)	1.90	0.80	1.84	1.58
Palmitic acid (C16:0)	24.00	23.77	27.45	26.29
Palmitoleic acid (C16:1)	2.40	1.57	3.37	3.66
Stearic acid (C18:0)	12.95	21.62	13.23	11.35
Cis - Oleic acid (C18:1 n9)	0.4	35.71	47.77	42.56
Linoleic acid (C18: 2)	0.3	12.00	3.26	9.09
Linolenic acid (C18:3)	0.55	0.39	0.11	0.26
Saturated fatty acids (SFA)	41.00	46.78	42.86	40.92
Monounsaturated fatty acids (MUFA)	44.70	37.28	52.30	47.35
Polyunsaturated fatty acids (PUFA)	14.35	15.94	4.84	11.73
UFA/SFA	1.44	2.38	1.33	1.44

 

1Vietnam: Anh et al.,2019 ; 2Australia: Navarro et al., 2021; 3China: Huang et al., 2012; 4Brazil: Alencar et al., 2011.

 

impact of environmental conditions on meat quality can be demonstrated through the varying protein contents of pork in some countries (Skobrák and Bodnár, 2012). The nutritional compounds of pork could significantly be changed with the age and live weight of pigs (Zomeño et al., 2023; Zullo et al., 2003). The percentage of protein in pork loin considerably increased when the live weight of baconer increased from 80-90 to 120-130 kg at slaughter while there was an opposite trend with ash (Zomeño et al., 2023; Zullo et al., 2003). It has been revealed that the fat content in pork significantly changes in accordance with the crude protein in daily diets of pigs (Adamczak et al., 2020). In particular, when crude proteins in the diet for pigs were at low (<15%), medium (15-25%), and high (>25%), fat content in pig meat changed at 20.1%, 17.9%, 14.7%, respectively (Adamczak et al., 2020). Fat content only contributes a small proportion in pork loin (Table 1) and its value can fluctuate from 1 to 15% (Skobrák and Bodnár, 2012).

The main composition of pork lipids is glycerol esters formed by three carboxylic acids (Ros-Freixedes and Estany, 2014). Its structure has a long and unbranched chain of carbon linked to a molecule called glycerol (Small, 1984) and a small percentage of phospholipids (Cui and Decker, 2016) and sterols (Addis, 1986), thus the fatty acids in a triacylglycerol have determined the physical properties and the role of lipids (Karupaiah and Sundram, 2007) in pork. Fatty acids (Table 2) are divided into saturated fatty acids (SFA), monounsaturated fatty acids (MUFA), and polyunsaturated fatty acids (PUFA) (Yi et al., 2023). Pork lipids have a better biological value from unsaturated fatty acids than from saturated fatty acids (Ros-Freixedes and Estany, 2014). Most of the latter were found in pork loin, such as palmitic acid (23.77-26.29%) and stearic acid (11.35-21.62 %) (Table 2). It has been indicated that the more these fatty acids are absorbed, the greater the risk of cardiovascular diseases (Zong et al., 2016). Lipoprotein is a crucial substrate for the transport of triglycerides and cholesterol to cells in the circulatory system (Havel, 1987) formed by the combination of lipids and proteins (Havel, 1987; Kris-Etherton and Etherton, 1982). The central hydrophobic core, is non-polar lipids composed of cholesterol esters and triglycerides, surrounded by a hydrophilic membrane consisting of phospholipids with the main compounds from free cholesterol and apolipoprotein (Feingold, 2021). Lipoproteins are classified into seven distinct types based on size, lipid composition, and apolipoprotein, of which three items are of more interest, including very low density (VLDL), low (LDL) and high-density lipoprotein (HDL) (Wood et al., 2011). The LDL is mainly responsible for the transportation of the cholesterol and it not only more easily enters the arterial wall but also binds more avidly to intra-arterial proteoglycans (Jaishankar et al., 2022), which is associated with increasing the accumulation of cholesterol in the arterial walls (Liu et al., 2020). Taken together from previous findings, these above reasons induce a tremendous effect on increasing the risk of atherosclerosis (Libby, 2021) and myocardial infarction (Byrne et al., 2022; Schubert et al., 2021) in consumer health problems. However, HDL plays an important role in reverse cholesterol transport to the liver (Voight et al., 2012), resulting in decreasing blood cholesterol (Soares et al., 2018; Voight et al., 2012), probably due to the role of stearic acid (van Rooijen et al., 2021). The process of endogenous monounsaturated fatty acid synthesis in tissues, is a chemical chain reaction from the necessary materials of palmitic acid and stearic acid (Figure 1) accompanied by myristic acid, to make short-chain saturated fatty acids easily absorbed in the digestive system of humans (Schmitt Jr et al., 1977).

 

Recently, it has been recognized there are heaps of benefits for human health from the functions of some UFAs (Mozaffarian et al., 2009), especially the omega-3 fatty acids with its structure always appeared the first double bond located in the third carbon (Bourre, 2004; Huang et al., 2020). (Mozaffarian et al., 2009) have shown that Omega-3 UFAs are conducive to preventing and protecting the circulatory system, as well as the beneficial effect of UFAs on anti-inflammatory activity and mechanism (Calder, 2015). It has been demonstrated there is a significant correlation between PUFAs and insulin sensitivity (Bhaswant et al., 2015). Otherwise, UFAs have a primary effect on both desirable and undesirable aromas and flavors in pork (Cheng et al., 2015) since the specific flavor of meat in each species is determined by liposoluble compounds in fat (Cui and Decker, 2016) and pork texture (hardness, springiness) (Anh et al., 2022). Numerous previous investigations have demonstrated the amount of UFA is a vital factor for formation of the tenderness of meat and the structure of skeletal muscle (Xu et al., 2021) as it is the main component of intramuscular fat (IMF). The infiltration and presence of UFA in pork muscle form the potential marbling in meat. The marbling score plays a key role in reflecting meat quality and the water-holding capacity of meat (Warner et al., 1997). In addition, iron atoms in pork are significantly related to the interconversion of myoglobin redox forms (Wilson and Reeder, 2022), which is a catalyst for the change of meat color after slaughtering process.

The lipid oxidation in pork after slaughter

After the slaughtering process, the metabolism of cell death is interrupted (Lima et al., 2013), and the reversible reactions using enzymatic would have converted the irreversible reactions due to the lack of both essential nutrients and oxygen (Schäfer et al., 2002). Consequently, the spontaneous breakdown of tissue strongly occurs (Kanner, 1994) by several steps, including (1) to suspense cellular metabolism, (2) to destroy the bonds of compounds in the structure of tissue, and (3) to degrade complex substances into simpler subunits (Tuan and Hien, 2004). Based on post-mortem changes in meat, these steps can be arranged into 3 phases, including pre-rigor, rigor mortis and post-rigor (Lawrie and Ledward, 2014) (Figure 2).

 

The period of rigor mortis primarily occurs to degrade both glycogen and ATP (Van der Wal et al., 1997) by muscle contraction from the combination of myosin and actin molecules, resulting in changing the muscles from this relaxed to rigor states (Ertbjerg and Puolanne, 2017). Glycogen is broken down to glucose in anaerobic conditions (Scheffler et al., 2011), then glucose is continuously transformed into pyruvate by the biochemical pathways of glycolysis (Chauhan and England, 2018) and relies on the impact of lactate dehydrogenase enzyme on conversion process into lactic acid which resulted in muscle acidification (Zequan et al., 2021). The acidification leads to advantageous and disadvantageous changes in both surface and inside of the meat (Lawrie RA, 1968) at the later stages. The transformation of actomyosin complex is an important biochemical process inside the meat. The actomyosin complex separates into actin and myosin which leads to increasing the water-holding capacity (Solomon et al., 1998), the decomposition of protein accomplished in the rigor off stage (Bray, 1966) to create some distinct kinds of amino

 

Table 3: List of volatile components derived from oleic, linoleic and linolenic acids.

Volatile components	Oleic acid	Linoleic acid	Linolenic acid
Alcohols	Hexanol Heptanol Octanol Nonenol	Butanol Pentanol	2 - Pentenol 1,3,6 - Nonatrienol
Aldehydes	Hexanal Octanal Decanal 2 - Decenal	Butanal Hexanal 2,4 - Decadienal Formaldehyde	2 - Pentenal 3 - Hexenal 2,4,7 - Decatrienal 3,6 - Nonadienal

 

acids namely hypoxanthine and glutamic (Tikk et al., 2006) concerned to the flavor meat. Therefore, the assessment of some potential parameters associated with tenderness, juicy levels, and odors in pork (Domínguez et al., 2019) are reliable and useful indicators to determine how the processes efficiently occurred inside the meat. It has been indicated that all undesirable changes have steadily happened in the final period of post-mortem changes in pork (Cheng et al., 2015). Lipid oxidation is the main process leading to reducing storage times (Mozuraityte et al., 2016) rather than the oxidation of proteins and vitamins, since UFAs are easily reacted with oxidizing agents, destroying lipid structure, causing texture and color changes and the pork taste could be changed from aroma to rancidity in meat (Pegg and Shahidi, 2012). Thus, controlling lipid oxidation plays a key role in ensuring stable meat quality and optimal efficiency for the meat industry (Nawar, 1969; Soladoye et al., 2015).

Autoxidation, enzymatically oxidized lipids, and photo-oxidation are the three main lipid oxidation pathways in pork (Domínguez et al., 2019). The autoxidation would have destroyed both cells and lipoprotein, causing the harmful products (Rao et al., 2011). Oxidized mechanisms of these pathways are similar and a chain reaction originating from UFA with three sequential stages including initiation, propagation, and termination. It initiates with the formation of free alkyl radicals in the first stage (Cheng et al., 2015), then creates peroxy radicals and hydroperoxides and some main products of lipid oxidation in the propagation stage, and the last stage to build up sub-primary products such as aldehyde, alcohols, volatile and nonvolatile compounds (Wójciak and Dolatowski, 2012) (Figure 2). Concerning lipid autoxidation, reactive oxygen species (ROS) which are undesirable by-products (its levels in overabundance or imbalance may lead to an increase in lipid peroxidation and DNA damage inside cell) of ATP production in mitochondria (Boyman et al., 2020), such as hydroxyl (OH-), singlet oxygen (O2-) (Estévez, 2015), and acid hydroperoxide (H2O2), are always present in the tissue. Phagocytosis is necessary to generate some free radicals to prevent the invasion and inhibit the activity of virus (Rosen et al., 1995). It has been reported that ROS reacts with polyunsaturated fatty acid to produce lipid peroxides in cell membranes (Figure 3). Autoxidation of lipids would have continuously happened while enzymatic oxidation released in the tissue by breaking down the lysosome membrane (Lorenzo and Gómez, 2012) is activated when the pH value of meat hits a bottom of 5.3-5.5 (Lametsch and Bendixen, 2001). The quick or slow accumulation rates of lactic acid in the muscle determine the degradability of the nutritional compositions in pork (Warner et al., 1997). Lipid-oxidized enzymes are a catalyst for association with oxygen and hydrocarbon chains of UFAs originating from triacylglycerol and phospholipid (Jin et al., 2010) to produce several products such as free fatty acids (FFAs) (Huang et al., 2012). These FFAs continue to be oxidized in order to synthesize an array of products (Cheng et al., 2015), especially the formation of flavor compounds (Fu et al., 2022) which include volatile components derived from oleic, linoleic and linolenic acids (Domínguez et al., 2019; Schaich, 2013) (Table 3). It has been demonstrated that seven of the twelve structures of odorants in pork broth are identified as products of lipid oxidation, such as Hexanal, 1-Octen-3-ol, (E-E)-2,4-Decadienal (Fan, 2021) whose compounds are all related to Omega-6.

 

Improving the sensory and nutritional quality of pork

The UFA plays multiple crucial roles for humans since it is the primary compound to engage in the brain structure (Blank et al., 2002) and tissue membrane (Wood et al., 2011), as well as supports to increase the immune system (Blank et al., 2002) for reduction of the risk of chronic disease (Huang et al., 2020) and other functions (Domínguez et al., 2019). Therefore, improvement of UFA in pork, especially Omega-3 fatty acids, may be an optimal solution to decrease the harmful effect of SFA on the physical and mental health of humans (Huang et al., 2020). Furthermore, it is also necessary to assess the meat quality parameters based on fatty acid content in muscle, the percentage of each distinct type of fatty acid, and the ratio among them (Anh et al., 2022). Although there have been numerous studies about the ratio of fatty acids in pork, a definitive conclusion has not been obtained yet and is still in discussion due to some inconsistent results (Anh et al., 2022; Engel et al., 2001; Juárez et al., 2011; Navarro et al., 2021). The UFA/SFA ratio in pork raised in Vietnam’s environment is about 1.44:1 (Anh et al., 2022); the PUFA/SFA ratio is 0.32-0.33:1 (Engel et al., 2001; Juárez et al., 2011)

 

while the ratio MUFA/PUFA of pigs fed the basal diet included wheat and canola oil during the period from 70kg to slaughter of 2.38:1 (Navarro et al., 2021). Moreover, a useful illustration of the ratio Omega-6/Omega-3 is 4.5:1 (Juarez et al., 2011) whereas there is only of 14.3:1 in the previous study (Romans et al., 1995).

On the other hand, the mechanism of fatty acid synthesis has been published (Ma et al., 2020) especially PUFA. There have been three different types of fatty acid desaturase in vivo found, including delta 5 (Δ-5), delta 6 (Δ-6), and delta 9 (Δ-9) (Nakamura and Nara, 2004). They play the vital role as catalytic enzymes for the reaction that removal of two hydrogen atoms from fatty acid to generate a double bond in the structure of products (Lee et al., 2016). The Δ-9 desaturase positively contributes to the biosynthesis of MUFA from SFA (Zhou et al., 2009) while the Δ-5

and Δ-6 desaturases are mainly responsible for long-chain polyunsaturated fatty acid biosynthesis since they are vital factors in converting LA and ALA into other unsaturated fatty acids (precursors of Omega-3 and Omega-6 group fatty acids) (Figure 4) (Mariamenatu and Abdu, 2021). Therefore, the supplementation of ingredients with high tion of long-chain PUFA in tissues (Huang et al., 2020). (Coates et al., 2009) have revealed that the Omega-3 index of pigs fed daily diets with supplementation of the long-chain Omega-3 PUFA at 41 mg/day is 4.4% and significantly lower than that of pigs under addition

 

Table 4: Previous investigations under pigs fed the daily diet containing linseed or linseed derivatives.

Environmental conditions					Treatments	References
n	Breeding Pigs	Based diet	Initial BW5, kg	Finish BW, kg
25	P1 x German LD2	Barley +	40	105	0 % linseed oil	Nwernberg et al., 2005
		Wheat + Soybean meal			5% linseed oil
144	-	Barley +	30	87	3 levels of 0, 50 and 100 g linseed/ kg	Mathews et al., 2007
		Wheat
43	LW3 x (LD x P)	Barley +	78.1	160	2.5% sunflower oil	Corino, 2008
		Wheat + Corn + Soybean meal			5% of whole extruded linseed
24	LD x NDL4	Corn + Wheat middling + Soybean	35	115	2 treatments:	Luo et al., 2009
					Fat power
					10% linseed
72	Czech LW x (Czech LW x Czech LD)	Barley +	28.7	110	2 levels of 0 and 150 g linseed/ kg	Okrowhlá et al., 2013
		Wheat + Soybean meal
48	LW	Barley + Soybean	79	150.5	5% of extruded linseed	Martini et al., 2020
					5% of extruded linseed + 200ppm of tocophenyl acetate
					5% of extruded linseed + 3g vegetal extracts

 

1P: Pietrain; 2LD: Landrace; 3LW: Lance White; 4NDL: New Dan Line; 5BW: Body weight.

 

at 185 mg/day (5.1%). Recently, it has been demonstrated a strong relationship between the diet with supplementation of ALA and the percentage of DHA in pork (Dugan et al., 2015). Thus, the DHA content considerably climbs by approximately 30% in pork after administration (Enser et al., 2000). Furthermore, the lower the ratio of n-6/n-3 PUFA in the diet is, the more significantly decrease the ratio of n-6/n-3 PUFA in pork (Yi et al., 2023) since this ratio has been associated with the presence of genes such as PPARy (Chan et al., 2022), FATP1 and FATP4 (Jensen et al., 1997), It has also been reported that there is a significant increase of the MUFA and PUFA contents in pork after the oleic acid addition to the daily diets of pigs (Yi et al., 2023). One of the important sources of PUFA supplementation is from natural ingredients such as linseed (Table 4) since it contains a high level of omega-3 fatty acid. Linseed oil accounts for 40% of the compounds in linseed (Farag et al., 2021), and the main component is a polyunsaturated fatty acid (73% of the proportion of linseed oil). Therefore, it has widely been demonstrated that the inclusion of linseed in the diet of pigs is a feasible solution for improving nutritional quality in pork (Wang et al., 2021) such as the increase of Omega-3 PUFA in tissue (Dugan et al., 2015; Huang et al., 2020; Yi et al., 2023). Similarly, the beneficial effect of dietary supplementation of macadamia oil on meat quality has also been clarified (Junior et al., 2022; Navarro et al., 2021). The percentage of C18:1 fatty acid (Oleic acid) and the ratio of MUFA/PUFA in total fat in pigs fed the diet added macadamia oil tend to be higher than those of pigs under diets added corn oil (Navarro et al., 2021). The diet supplementation of macadamia oil also contributes to significantly improving the flavor, aroma and tenderness of pork (Navarro et al., 2021).

On the other hand, it has been recognized that the disadvantage of the high unsaturated fatty acid content in pork is associated with the state of lipid oxidation (Domínguez et al., 2019) which undesirable consequences have a negative effect on the sensory and nutritional quality of meat (Nawar, 1969). Therefore, dietary supplementation of antioxidants may be a feasible solution to reduce the lipid oxidation through the prevention of the formation of free radicals (Chen et al., 2023; Domínguez et al., 2019). The oxidative stability of meat is recorded when pigs have been fed a diet of antioxidants (Li and Liu, 2012) since the first priority of free radicals react with antioxidants (Lobo et al., 2010). Alpha-tocopherol is universally recognized as an effective antioxidant (Jensen et al., 1997) to neutralize free radicals during post-mortem storage after slaughter (Li and Liu, 2012). TBARS index in pork is significantly decreased as the dietary supplementation of Alpha-tocopherol to pigs (Lu et al., 2016) in six days of refrigeration (Phillips et al., 2001) by thiobarbituric acid reactive substances. In addition, 100mg/tons feed of alpha-tocopheryl acetate is recommended as a sufficient level to ensure meat quality and oxidative stability of pork (Jensen et al., 1997). The combination of linseed oil and alpha-tocopherol in feed not only significantly modifies the ratio of n-6/n-3 fatty acids but also reduces the lipid oxidation when pigs are fed under diets enriched with omega-3 fatty acids (Hoz et al., 2003). A similar positive result is reported by (Monahan et al., 1992) with the dietary supplementation of soybean oil and alpha-tocopherol at 200 mg/kg. Furthermore, the deposition of alpha-tocopherol in pig muscle is significantly improved in the diet added with alpha-tocopherol (around 2.8 times higher than those of other diets) (Monahan et al., 1992). Synthetic antioxidants such as butylated hydroxyanisole (BHA) and tert-butylhydroquinone (TBHQ) (Mika et al., 2023) can also prevent the lipid oxidation by inhibiting autoxidation and preventing the appearance of free radicals (Xu et al., 2021), leading to the formation of a more stable compound. However, consumers are still concerned about the negative impact of synthetic antioxidants on human health (Kornienko et al., 2019), so current research applications of natural antioxidants have still been interesting in the livestock industry (Chen et al., 2023; Manessis et al., 2020; Petcu et al., 2023).

Recently, there have been multiple studies to evaluate the potential of phytogenic compounds, including phenolic compounds and essential oils (Puvača et al., 2013), to improve the subtable oxidation in pork (Botsoglou et al., 2013; Giannenas et al., 2005). The minimal loss of nutritional components after slaughter in the period of storage can be achieved in two ways, including anti-oxidation (Kiokias et al., 2020) and anti-bacteria (Fasseas et al., 2008) to prohibit contamination and growth of spoilage microbes on the surface meat (Govaris et al., 2005) throughout pre-slaughter and post-slaughter. The dietary supplementation of phytogenics has witnessed an upward trend in the deposition of alpha-tocopherol in tissue (Botsoglou et al., 2013). Phenolic acid, which is one of the phenolic compounds (Anh et al., 2022), has been known to have the ability to reject free radicals and protect membranes (lipoproteins) (Kiokias et al., 2020). There are many classes of phenolic acids, such as caffeic acid (in bananas) (Siriamornpun and Kaewseejan, 2017), coffee (Deotale et al., 2019), ferulic acid (in cereal grains, linseed, and bananas) (Sgarbossa et al., 2015; Siriamornpun and Kaewseejan, 2017) and rosmarinic acid (in rosemary, sage, and musk) (Kiokias et al., 2020). Phytogenic bioactive compounds such as tannins, lignans, flavonoids, and allicin (Table 5) can cause the profile of fatty acids to significantly change due to the deposition of IMF in pork loin (Yang and Zhang, 2015) resulting in an increase in the marbling score. Pigs fed a dietary supplementation of 80mg cinnamaldehyde/kg (Luo et al., 2009; Yu et al., 2017) or with 2.5mg mixed-herbs/kg (Yu et al., 2017) significantly increase the marbling score. The addition of a herbal mixture (peppermint, chamomile, thyme, coriander, caraway, couch grass, savory, milk thistle

 

Table 5: Diet supplementation with phytogenics on meat quality indicators.

Pig	Number (pigs)	Live weight (Initial - Finish) (kg)	Durian	Natural sources	Treatments	Result	References
Retinto Iberian	90 barrows	90 - 150	70 - 80 days	Acorns (enriched phenolic compounds)	3 production systems: - Montanera (free-range system and feeding based on acorns and grass) - Recebo (free-range system and nutrition based in combination of acorns, grass and mixed feeds) - Intensive (confinement with mixed feeds)	Increase: The contents of phenolic compounds, alpha-tocopherol; MUFA and PUFA in pork Decrease: SFA	(Tejerina et al., 2012)
P x LW1	27 barrows	7 - 131.34	35 - 180 days	Carob pulp (including tannin)	3 diets: - Control: Based diet - Carob 8%: Based diet + 8% Carob - Carob 15%: Based diet + 15% Carob	Feeding carob-containing diets: - Increase: MUFA, n-3 PUFA - Decrease: SFA, n-6/n-3 PUFA	(Inserra et al., 2015)
D2 x (L3 x Y)	96 barrows and gilts	25.46-108.51	16 weeks	Artemisia capillaris (leaves) Acanthopanx senticosus (leaves and roofs)	3 diets: - CON: Based diet - NH: Based diet + 0.05% natural herbs - FH: Based diet + 0.05% fermented herbs	Compare NH, FH with CON: - Increase: PUFA, PUFA/SFA ratio - Decrease: SFA, TBARS index	(Lei et al., 2018)
D x (L x Y4)	450 barrows and gilts	7.21 - 103.2	28 - 154 days	Ginger (Zingerone), Garlic (Alicin), Tumeric (Curcumin)	3 diets: - C: Based diet - CHE 3: Based diet + 3g CHE/kg - CHE 5: Based diet + 5g CHE/kg	Feeding herbs-containing diets: - Increase: Sum of Omega -3 , Omega - 6, Omega - 9; MUFA; UFA/SFA - Decrease: SFA	(Anh et al., 2022)

 

1LW: Lance White; 2D: Duroc; 3L: Landrace; 4Y: Yorshire.

 

Table 6: Correlations between natural antioxidants and indicators associated with meat quality.

Correlations	Natural Antioxidants	Authors
Positive	Phenolic acid	(Botsoglou et al., 2004; Fasseas et al., 2008; Puvaca et al., 2013; Yang and Zhang, 2015; Siriamornpun and Kaewseejan, 2017; Deotale et al., 2019; Kiokias et al., 2020; Serena et al., 2020)
	Tocopherol	(Apple et al., 2007)
	Cinnamaldehyde	(Frankič et al., 2010; Kolodziej et al., 2011; Yu et al., 2017; Luo et al., 2020)
	Organosulfur compounds	(Byun et al., 2001; Janz et al., 2007; Park and Chin, 2014; Samolinska et al., 2020)
	Curcumin	(Joo et al., 2002; Zhang et al., 2020)
Negative	Curcumin	(Mancini et al., 2016)

 

endosperm, and garlic bulb) into the daily diet at 2% on DMI improved the ratio of n-6 and n-3 PUFA in the pork, better human health (Paschma and Wawrzyński, 2007).

There have been a variety of amino acids in herbs, especially in garlic, found and published in previous studies that give positive benefits for humans (Liu et al., 2020), such as S-allyl cysteine, glutamic acid, arginine, aspartic acid, etc (Kodera et al., 2002; Liu et al., 2020). Methionine accounts for 0.55 g/100 g crude protein in garlic and is higher than that of cysteine (0.38 g/100 g protein), while the arginine concentration is the highest in ginger (Uchegbu and Iloeje, 2014). A free group of amino acids is one of the main materials of the Maillard reaction and Strecker degradation (Sun et al., 2022), whereas alpha aminoketone is a product formed by this reaction (Resconi et al., 2013), having an essential impact on meat flavor compounds (Shahidi et al., 2014). In recent decades, there have been a large number of numerous studies carried out to find out the correlations between natural antioxidants and indicators associated with pork quality among different natural kinds (Table 6), including phenolic acid (Botsoglou et al., 2004; Fasseas et al., 2008; Puvaca et al., 2013; Yang and Zhang, 2015; Siriamornpun and Kaewseejan, 2017; Deotale et al., 2019; Kiokias et al., 2020; Frankič et al., 2010), tocopherol, cinnamaldehyde (Frankič et al., 2010; Kolodziej et al., 2011; Yu et al., 2017; Luo et al., 2020), organosulfur compounds (Byun et al., 2001; Janz et al., 2007; Park and Chin, 2014; Samolinska et al., 2020) and curcumin (Mancini et al., 2016; Zhang et al., 2020). Up to now, although a causal relationship is still not established, there has been a consensus from a majority of the above studies that the positive correlations are found in between natural antioxidants and indicators associated with meat quality, except for one study in curcumin (Mancini et al., 2016).

In general, the amount of lipids in pork is significantly increased through the addition of ingredients with high UFAs into the daily diet, but the higher the unsaturated fatty acid is, the more strongly lipid oxidation occurs. Natural antioxidants are well known to be effective in preventing the lipid oxidation by inhibiting the autoxidation and the appearance of free radicals and enhancing pork flavour. Therefore, it seems that the combination of ingredients enriched with unsaturated fatty acids and natural antioxidants is a feasible solution to not only improve the chemical composition of pork but also optimize the storage time after slaughter. At present, however, actual interactions and mechanisms are poorly understood in the combination and require further investigation to fully ascertain.

CONCLUSIONs AND RECOMMENDATIONS

Pork is classified as a nutrient-rich food and does not contain antinutrients. Although it has been demonstrated to play an important role in numerous biological processes, consumers are concerned about the adverse effects of pork consumption on the health due to saturated fatty acids, while unsaturated fatty acids are widely recognized to have higher biological value. Recent research results have shown that using ingredients rich in UFAs, such as macadamia will improve this ingredient in pork. The limitations of this research are that high UFA in pork causes the oxidation process to occur faster, changing the color and flavor of pork. Therefore, our review under the comprehensive data from previuous publised findings suggest the trend of natural antioxidants are effective in preventing the lipid oxidation by inhibiting autoxidation and preventing the appearance of free radicals and enhancing pork flavour through joining in the structure of flavour compounds to form phytogenics extracted herbals. Furthermore, it is important and necessary to apply a feasible solution through the dietary combination of UFA-containing sources and natural antioxidants in the pig industry to improve the quantity and quality of the pork.

NOVELTY STATEMENT

Systematic review under comprehensive discussion within all aspects and mechanisms associated with currently new research trend for pork quality improvement through dietary supplementation of ingredients enriched with unsaturated fatty acid and natural antioxidants

AUTHOR’S CONTRIBUTIONS

Anh Thi Ngoc Dang and Hai Thanh Nguyen were responsible for the concept, manuscript preparation and edition. Cuong Kien Nguyen and Duy Ba Ngo contributed to brushing up on the quality of this review. All authors have read and approved the final version of the manuscript.

Conflict of interest

The authors declared no conflict of interest.

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