Using Natural Antioxidants in Meat and Meat Products as Preservatives: A Review

| Lipid oxidation is one of the most important problems that decrease the shelf life of meat and meat products. Antioxidants are used to reinstate free radicals thereby retarding lipid oxidation, delay development of unpleasant-flavors, and improve color stability.Application of synthetic antioxidants to mitigate oxidative damage may consider unsafe for consumers. Furthermore, the recent growing in the understanding of the consumers about these hazards resulted in the replacement ofsynthetic antioxidants with natural bioactive compounds. Plant materials are rich sources of bioactive phenolic compounds; hence they can be an effective alternative to synthetic antioxidants. This review presents an overview regarding the new advances in the application of natural antioxidant compounds such as herbs, spices, fruits, plant essential oils and extracts in meat and meat products to improvetheir quality and shelf-life.

products. Different synthetic antioxidants, such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), tert-butyl hydroquinone (TBHQ), propyl gallate (PG), and nitrite are used in the meat industry. Nowadays, because of the possible health risks and toxicity of these synthetic compounds on human health and increasing tendency to consume natural components, their use has been limited. Several types of research have been conducted to find a new and natural source of antioxidants to replace with synthetic antioxidants (de Florio Almeida et al., 2017;Ehsani et al., 2012).
There are different bioactive compounds in plant sources such as phenolic compounds, carotenoids, tocopherols, and etc. Nowadays EOs are widely used in the food industry because of their ability in retarding the food spoilage, improvement of organoleptic quality, and pathogen growth inhibition . These compounds are classified as "Generally recognized as safe" (GRAS) food additives for human consumption with pharmaceutical, antimicrobial, and antioxidant properties by the Food and Drug Administration (FDA) . Plant polyphenols may be offered as alternatives to EOs. It has been reported that polyphenols have a variety of biological effects such as antioxidant, anti-carcinogenic, anti-inflammatory, and antimicrobial activities . In this review, the potential application of different bioactive compounds derived from plant sourcesin the meat and meat products have been reported. Furthermore, this review aimed to study the effect of replacing natural antioxidants with synthetic components to delay the oxidative reactions in meat and meat products.

MechanisMs of lipid oxidation
Lipid oxidation is initiated byionized hydrogen (H + ) which is separated from an unsaturated fatty acid and form an alkyl radical (R o ). Lipid radical's formation is thermodynamically undesirable and is usually initiated by the presence of other radical compounds (R o ), single oxygen, and decomposition of hydroperoxides (ROOH) or pigments that act as colorants (Ahna et al. 2007). The alkyl radical (R o ) change the position of the double bond (Cis to trans) and produce a conjugated diene system. The R o can react with oxygen to form a high-energy peroxyl radical (ROO o ) (Chaijan, 2008). The peroxyl radical can then react with another hydrogen atom (H + ) from another unsaturated fatty acid to form a ROOH and a new R o . This process propagates to another fatty acid (Falowo et al., 2014).

consequences of lipid oxidation on Meat and Meat products quality
Severalfactors can affect lipid oxidation in meat and meat products including high ratio of polyunsaturated fatty acids (PUFAs) as components of membrane phospholipids, lack of antioxidants, high concentrations of pro-oxidants and reactive radical species, presence of high amounts of salt (NaCl) and free molecular oxygen that is usually entered into meat mixture during processing. Researchers have proved that salt can reduce the activity of glutathione peroxidase, superoxide dismutase, and catalase ( Jiang & Xiong 2016). Oxidative deterioration of meat and meat products results in the development of off-flavor, discoloration, formation of toxic compounds, loss of nutrients, drip losses and thus shorten the shelf life (Contini et al., 2014;Palmieri et al., 2007). Under normal physiologic conditions, the molecular oxygen exposes a series of reactions that causes generation of free radicals. During the metabolic reactions, a small amount of the consumed oxygen is changed to form reactive oxygen species (ROS). Free radicals, especially, ROS and reactive nitrogen species (RNS) which can interact with fatty acids, nucleic acids and proteins, take a part as intermediate agents in several homeostatic processes (Moylan et al., 2014). In general imbalance between the production of ROS and antioxidant leads to oxidative stress, which often causes functional and structural damages to muscle organelles, cells and tissues. Myofibril protein can be affected by ROS during the storagewhich affects meat quality and damage cellular structure. Evidence showed that ROS reduce collagen synthesis in the muscle, which increases meat toughness and decrease solubility of collagen (Falowo et al., 2014;Archile-Contreras and Purslow, 2011).

oxidation reaction in Meat saMple
The word 'antioxidant' means any substance that can either delay or prevent the oxidation of an oxidizable substrate. Various factors can promote lipid oxidation including presence of oxygen, metal ions, moisture, heat, and light, therefore to prevent or retard oxidation in susceptible foods, oxygen and metal catalysts should be removed and foods must be kept at low temperatures and be protected from light (Rather et al., 2016).
Antioxidants prevent lipid peroxidation by preventing a chain reaction, scavenging ROSs, breaking the auto-oxidative chain reaction, quenching O2-radicals and preventing peroxides developments, and binding to catalysts such as metal ions. There are large numbers of components that have been proposed to possess antioxidant activity (Shah et al., 2014). Some natural antioxidants inhibit the development of free radicals and promotion of ROS. The antioxidant activity of them is due to their molecular structure, -OH groups and ortho-3, 4-dihydroxy structures which increase the antioxidant activity of natural components. Plant pigments such as anthocyanins have -OH groups, which can donate H· (Rather et al., 2016).
The most important antioxidants are those that interrupt the free radical chain reactions. These compounds usually

Advances in Animal and Veterinary Sciences
May 2019 | Volume 7 | Issue 5 | Page 419 contain aromatic or phenolic rings which donate H + to the formed free radicals during oxidation and are converted to radical intermediates. These intermediate radicals are stabilized by the resonance (delocalization) of the electron within the aromatic ring and formation of quinone structures (Maqsood et al., 2014).

natural antioxidant in Meat and Meat products
Plants are potential source of valuable bioactive substances and have been evaluated as natural antioxidants to improve the chemical quality of meat and meat products (Shah et al,. 2014). Nowadays, many studies have been done to use different medicinal plants as potent antioxidant sources for food preservation and improve nutritional quality of meat products. Most of the plants (herbs and spices) have relatively high macronutrients (such as protein, fat, and carbohydrate), micronutrients (minerals and vitamins) and less anti-nutritional properties. Additives with antioxidant properties have been developed to control lipid oxidation and formation of the secondary breakdown products in foods. The total antioxidant potential of plant materials such as culinary herbs, spices, vegetables, as well as fruits and oilseed products is related to ascorbic acid (vitamin C), alpha tocopherol (vitamin E), beta-carotene (vitamin A precursor), numerous flavonoids, and other phenolic compounds (Rather et al., 2016).
Spices and herbs are used in foods for their flavor and often contain high concentrations of phenolic components with an extreme H-donating activity.The major anti-oxidative phenolic compounds in plants can be classified into groups including phenolic diterpenes (carnosic acid andcarnosol), flavonoids (quercetin and catechin), phenolic acids (gallic, rosmarinic acids and caffeic acid), and volatile oils (carvacrol, eugenol, thymol, and menthol) (Falowo et al., 2014). The plant extracts obtained from different sources such as fruits, vegetables, herbs, and spices have been proven to possess strong antioxidant activity because of their high content of phenolic compounds. These extracts are prepared from the plant materials by using different solvents and extraction methods. Extraction process should provide the highest yield and quality of target compounds. There are many techniques to obtain antioxidants from plants, such as supercritical fluid extraction (SFE), Soxhlet extraction (SE), ultrasound-assisted extraction (UAE) and subcritical water extraction (SWE) and etc. In general, in solvent extraction process the plant materials are cleaned, washed, dried, and ground into fine powder.
There are different solvents for extraction purpose such as acetone, methanol, pure ethanol, 70, 80, 90% ethanol, dimethyl sulfoxide and water (Shah et al., 2014). Recently, green technologies such as SFE or pressurized liquid extraction (PLE) often along with the use of GRAS solvents as water, carbon dioxide (CO 2 ) or even ethanol have been developed. There are different and controlled combinations of temperature and pressure in PLE method, which can improve extraction efficiency. In fact green extraction techniques are effective assays to extract bioactive compounds from natural sources (Alañón et al., 2017). Plant essential oils are secondary metabolites which are applied as flavoring and preservative agents. Different properties of EOs are due to flavonoids, alkaloids and terpenoids as the most important secondary metabolites in EO . In order to decrease or inhibit oxidative reactions in meat foods, antioxidant components are usually used at an average level. Higher concentration may cause various side effects through pro-oxidative action. (Falowo et al., 2014). Data from scientific reports indicate that most plants contain a wide variety of components with antioxidant activity. Fruits, oilseeds, herbs and spices extracts and essential oils are the most important antioxidant sources used in meat and meat products.

fruits extracts
In general, fruits and vegetables are excellent sources of antioxidants. Pomegranates, strawberry, kinnow, acerola, white grapes, plums, black currant, annatto, bearberries, banana, and sapodilla are some samplesthat contain relatively high concentrations of antioxidants. These fruits have been well documented for uses in industry considering their antioxidant activity (Table 1). Annatto (Bixaorellana L.) seeds powder which has been used as a natural coloring agent in food contains bixin and nor-bixin apocarotenoids as antimicrobial and antioxidant agents. Cuong and Chin (2016) showed that this additive can retard lipid and protein oxidation in pork patties. Acerola (Malpighia emarginata L.) fruit extract with a high content of phytochemicals is well known as an excellent food source of vitamin C. It was shown that Acerola can improve color and lipid stability and decrease rancid flavor of raw salted beef patties without affecting microbial load (Realini et al., 2015). Grapes are recognized as a power house of antioxidants. Grape by-products such as grape pomace (wine pomace) are a rich source of phenolic compounds with great medicinal properties, but usually is wasted from juice/wine processing industries. García-Lomillo et al. (2017) indicated that beef patties formulated with skin fraction of red wine pomace had the lowest lipid oxidation. Munekata et al. (2015) indicated that application of peanut (Arachishypogaea L.) skin extract (PSE) as a natural antioxidant in cooked chicken patties can prevent lipid oxidation during refrigerated storage. The presence of bioactive compounds such as phenolic acids, stilbenes, flavan-3-ols, biflavonoids, isoflavones, flavanols, and flavones in PSE makes it a natural alternative for synthetic antioxidants which reduces the loss of redness and prolonging the shelf life of sheep patties (Munekata et al., 2016).

Advances in Animal and Veterinary Sciences
May 2019 | Volume 7 | Issue 5 | Page 420  Grape seed Dry cured sausage "chorizo" Meat-based ready-toeat meals Improved the quality and increased the shelf life of products.
The added agents did not change the sensorial properties and were stronger than sodium ascorbate to retard the lipid oxidation (Lorenzo et al,.   Raw lamb patties This study show that the grape and olive pomaces extracts could be an effective additive to replace sodium ascorbate in meat products. (Andrés et al,. 2017)  Cinnamomum zeylanicum essential oil Lyoner-type sausage Improved sensorial properties, did not modify protein, ach and fat content, slowed rates of oxidation (

oilseeds
Oilseeds are the basis for a wide range of foods, animal feeds and other products. Grape seed, soybeans, Adzuki bean and many vegetable seeds are used as a potential source of seed oils. Grape seed extract) GSE (is a rich antioxidant source. Several studies proved antioxidant and antimicrobial effects of GSE on meat and meat products such as dry-cured sausage "chorizo". It was also shown that combination of Clove EO with different concentrations of GSE can be effective against spoilage microorganisms in raw materials, such as buffalo patty (Tajik et al., 2014). Soybean oil is another vegetable oil extracted from the soybean seeds (Glycine max). Soybean oil contains more than 60% PUFA; however, it has been shown that higher concentrations of soybean oil doesn't affect oxidation rate of mortadella (Morais et al., 2013). Menegas et al. (2013) indicated that the use of standard amounts of corn oil in fermented chicken sausages caused no significant chemical, microbiological, physical, or sensory changes during storage. Table 2 shows some researches about the use of seed oil as antioxidants in meat and meat products.

herBs and spices extracts
Several studies showed that extreme antioxidant activity has been found in herbs, spices, and extracts so they can be used as natural antioxidants in meat and meat products. Soy sauce contains several antioxidants such as melanoidins, phenolic compounds, and free amino acids. The use

Advances in Animal and Veterinary Sciences
May 2019 | Volume 7 | Issue 5 | Page 424 of soy sauce in raw beef patties showed decreasing in lipid oxidation of meat products (Kim et al., 2013). Herbal tea prepared from Camellia sinensis is a rich source of polyphenolic compounds such as catechin and flavonoid compounds. Itcould be replacedwith synthetic antioxidants in frozen beef patties (Reihani et al., 2014). The antioxidant properties of rosemary extract (RE) are due to the presence of phenolic diterpenes, such as carnosic acid and carnosol. Nitrite concentration decreases dramatically when RE is added to liver pates without a negative effect on color (Doolaege et al., 2012). De Florio Almeida et al. (2017) showed that lyophilized bee pollen (LBP) contains antioxidant compounds such as vitamin Cas well as polyphenols.

essential oils
Many plantessential oils (EOs) are known as rich antioxidant sources (Coutinho de Oliveira et al., 2012;Shah et al., 2014). Cinnamon (Cinnamomum Zeylanicum) contains phenolic and polyphenolic compounds and act as a good inhibitor of primary and secondary oxidation products in Lyoner-type sausage (Aminzare et al., 2015). Thymol, p-cymene, linalool, and carvacrol available in Satureja Montana L. EO could reduce the use of sodium nitrite of mortadella-type sausages (Coutinho de Oliveira et al., 2012). Petrovskáklobása is a traditional dry fermented sausage that has been manufactured for over 250 years. It is produced from pork meat, spices and fat. Coating with chitosan incorporated with oregano (Origanum vulgare) EO indicated a reduction in lipid oxidation of dry fermented sausages (Krkić et al., 2013). Application of some important essential oils in meat and meat products are listed in Table 4.

dietary fiBer
The concept of antioxidant dietary fiber (ADF) has been accepted as a natural product with both of the physiological and antioxidants properties. Dried fruit, extracts and/or powders of some plants or their by-products can be good sources of ADF (Eskicioglu et al., 2015). Ding et al. (2015) indicated that litchi (Litchi chinensis Sonn.) is a fiber rich of polyphenols and is considered as an effective natural antioxidant which reduce lipid and protein oxidation of frozen cooked meatballs. Sage (Salvia officinalis) contains phenolic compounds, such as carnosol, carnosic acid, and rosmarinic acid. During storage of refrigerated Chinese-style sausage formulated with ground sage, areductionin TBARs values and textural deterioration and no negative effects on the sensory properties were observed (Zhang et al., 2013). Tomato (Solanum lycopersicum) pulp powder is rich in carotenoids (particularly lycopene, β-carotene, phytoene, and lutein), flavonoids, vitamins E and C, and fiber. The use of this natural additivecould decrease nitrite supply in pork luncheon roll (Hayes et al., 2013). Table 5 indicates some researches about the use of by-products as antioxidants in meat and meat products.

concluSIon
Oxidation is a major problem that decreases the shelf life of meat and meat products. Synthetic compounds are used to delay oxidation reactions. However, because of the increasing consumer's demand to replace synthetic antioxidants with natural bioactive compounds a wide variety of researches have been done to find new and natural sources of antioxidant compounds. There are different chemical compounds derived from plants that can be used in meat and meat products as natural antioxidants which have been isolated from different plant parts like leaves, stems, roots, fruits, bark and seeds. It should be considered that the use of these natural additives is limited by their extreme flavor, which can have adverse sensory effects on meat and meat products. Future studies should be done toward the investigating of new technologies such as high pressure processing, pulsed electric fields and ultrasound combined with natural antioxidant in order to improve the antioxidant properties in meat and meat products.