The Implications of Replacing Synthetic Antioxidants with Natural Ones in the Food Systems

Abstract

Antioxidants are substances that delay/prevent the autoxidation process of other compounds or neutralize free radicals which are applicable in food processing industries to hinder oxidation, enhance flavor, aroma and color. Types of antioxidants include synthetic and natural ones as the major types, and others as endogenous, exogenous, dietary antioxidants etc. Whereas synthetic antioxidants are products of artificial synthesis, natural antioxidants are products of natural synthesis occurring in plants, animals, and also in bacteria. Though synthetic antioxidants have been associated with side effects that affect health at the long term, their usage in food system was higher from the inception of applications of antioxidants as food preservatives. Hence, the increasing suggestion of their replacement with the natural ones, which the literature associated with benefits like enhancement of food quality, broadening orientations of food to include health interest, promotion of eco-friendly food system/circular economy, processing more composite foods for maximum exploitation of natural antioxidants, in addition to, repositioning food systems as means of reducing/preventing occurrences of some chronic diseases. The replacement may promote interest in increasing values derivable from food systems and facilitate the accomplishment of food safety and food security in every society that makes it part of its food policy.

1. Introduction

The major drive of recent developments in food processing and storage activities is, undoubtedly, to produce food products that have the potential of providing required nutrients and bioactive compounds in order to reduce increasing lifestyle diseases like cancers, cardiovascular, diabetes, and others. Bioactive compounds are non-essential biomolecules that have biological values beyond their calorie content found in foods that are capable of modulating metabolic processes resulting in the promotion of better health [1]. Antioxidants are bioactive compounds contained in foods, though not considered as part of nutrients, but by their antioxidative activities, are capable of enhancing the foods’ keeping quality or promoting the consumers’ health. Sardarodiyan and Sani [2] posit that antioxidants have become an indispensable group of food additives mainly because of their unique properties of extending the shelf-life of food products without any adverse effect on their sensory or nutritional qualities. Studies about antioxidants have shown that they are chemical compounds that are capable of hindering the generation of reactive species and their derivatives, either in the food systems or in the human body. They are categorized into two major groups which include synthetic and natural antioxidants, based on their sources. Natural antioxidants are produced by natural molecular formations in plants, animals, mushrooms, microorganisms like algae and bacteria and are thus extracted directly from organic sources such as fruits, vegetables, grains, and meat. Synthetic antioxidants are artificially synthesized by combinations of some chemical compounds in laboratories for use, mainly, in the preservation of foods. Though both categories of antioxidants are assumed to perform the same function in food systems, they have a distinct effect. According to the literature, in terms of zero tolerance to side effects and contribution to delay or prevention of occurrence of chronic diseases, natural antioxidants are more effective; while in terms of preservation of high lipid food products synthetic antioxidants are more effective. Morton et al. [3] corroborated with this assertion by reporting preference in the use of synthetic antioxidants in preserving foods with high rancidity levels to natural antioxidants usable in preserving hydrogenated oils with lower rancidity levels.

1.1 Definition of antioxidant

Antioxidants are substances that prevent or retard oxidative activities in foods or body systems. Halliwell [4] and Arun and Abdul Azeez [5] reported that they are usually present in relatively small concentrations but are capable of frustrating oxidative activities in the systems. Tuberoso et al. [6] and Atta et al. [7] mentioned them as resources for use in preventing or greatly retarding the oxidation of easily oxidizable materials such as fats (and or peroxidation of lipids in food products and cells of the body systems. They are also defined as substances that engage harmful forms of oxygen to prevent them from harming the cells of either the food products or those of the body of food consumers. Kebede and Admassu [8] stated that antioxidants are capable of slowing down the autoxidation process of other compounds or neutralize free radicals. Although Becker et al. [9] and Halliwell [10] specified the above definition in the context of the biological system, Atta et al. [7] alluded to it as a broader definition encompassing many vulnerable macromolecules (e.g. DNA, lipids and proteins) that can be affected by oxidation. Such broad definition means that compounds that inhibit specific oxidizing enzymes, react with oxidants before they damage molecules, sequester dangerous metal ions or even repair systems such as iron transport proteins, can fit into the definition [7]. Ihekoronye and Ngoddy [11] defined them as substances that retard the rate of oxidation which serve two principal functions: breaking the oxidation chain by containing free radicals or acting as hydrogen donors and facilitating the breakdown of peroxides into stable substances that inhibit further oxidation. Atta et al. [7] referred to the above description as the mechanistic definition of antioxidants. The definition considers radical scavenging capacity or amount of free radical captured by antioxidant food components [12]. Asimi et al. [13] considers antioxidants as compounds or systems that can safely interact with free radicals generated in the food products or by metabolic activities to prevent them from reacting with the cells and cause damages, in the case of the body. Their affinity with the free radicals facilitates their disposition to mop up the radicals generated by metabolic processes to protect the cells. Antioxidants, indeed, are substances that at low concentrations retard the oxidation of easily oxidizable biomolecules [14] such as lipids and proteins either in food products or in living cells of the body system to discourage adverse effects of oxidation. Antioxidants act at different levels in the oxidative sequence involving lipid molecules [2]. Bontempo et al. [15] reported several ways they function including reducing oxygen concentration, intercepting singlet oxygen (1O₂), scavenging initial radicals like hydroxyl radical to avoid initiation of first-chain reaction, binding metallic ion catalysts, decomposing primary products of oxidation to non-radical species and breaking chain reactions to prevent continued hydrogen abstraction from substrates. The necessity to produce healthier foods to discourage occurrences of lifestyle diseases and their associated increasing intake of drugs propels consideration for replacing synthetic antioxidants with the natural ones in the food system.

2. Operational mechanism of antioxidants

The reduction or stoppage of oxidative processes by antioxidants, in any system, follows two principal mechanisms of action. Kebede and Admassu [8] reported a chain-breaking mechanism as the first action in which primary antioxidants donate electrons to the free radicals present in the system. The ways they achieve this include stoppage of formation of free radicals, providing electrons to the existing free radicals to stabilize them and checkmating their reactivity. A free radical can be defined as, “any molecular species capable of independent existence that contains an unpaired electron in an atomic orbital and capture electrons from other substances in order to neutralize themselves” [16]. Atta et al. [7] referred to this action as neutralization of free radicals and identified two major pathways through which this is accomplished to include chain-breaking and preventive processes. In chain-breaking free radicals release or abstract electron to form second radical which does the same thing to the third molecule to continue to generate unstable products to propagate the chain of reactivity and oxidation processes. The free radical has the ability to donate or to accept an electron from other molecules [17]. This stabilizes the free radical at the beginning but starts to produce another in the process [14]. The moment a chain reaction begins, thousands of free radical reactions can occur within a few seconds on the primary reaction [18].

Antioxidants readily donate an electron to the free radicals to get them stabilized. This assertion is in agreement with the report of Brewer [19] that the propagation of free radical chain reaction can be minimized by the donation of hydrogen from the antioxidants and the metal chelating agents. The preventive pathway of antioxidants entails the removal or scavenging of free radicals to prevent their interaction with food substrate. The view of Nawar [20] about the mechanisms of antioxidants indicated that antioxidants scavenge species that initiate peroxidation, chelate metal ions, and disable their potential to generate reactive species or decompose lipid peroxides, quench or prevent the formation of peroxides, break the autoxidative chain reaction, and/or reducing localized O₂ concentration. This assertion described by Kebede and Admassu [8] as the second mechanism of action of antioxidants, entails quenching chain initiator mechanisms that incidentally eliminates initiators of reactive oxygen species (ROS) and reactive nitrogen species (RNS). It is worthy to mention here, according to Pisochi and Pop [21] and Perez and Aguilar [22], that free radicals are derived from oxygen, nitrogen, and fsulfur molecules and, hence the free radicals constitute groups of molecules called reactive oxygen species, reactive nitrogen species, and reactive sulfur species. Atta et al. [7] stated that free radicals of ROS include superoxide anion (O₂−•), perhydroxyl radical (HO₂•), hydroxyl radical (·OH), nitric oxide and other species such as hydrogen peroxide (H₂O₂), singlet oxygen (O₂), hypochlorous acid (HOCl) and peroxynitrite (ONOO–). According to them, whereas RNS are products of the reaction of nitric oxide with O₂−• to form ONOO–; RSS is derived from the reaction of thiols with ROS.

The mechanisms of antioxidants are further explicable with identification of three stages of mechanisms of chain reactions which according to the reports of Rosenblat and Aviram [23], Polumbryk et al. [24], and Kebede and Admassu [8] include: initiation, propagation, and termination stages. In the initiation stage, the abstraction of the hydrogen atom from the system generates free radicals to initiate chemical reactions of oxidation activities. The presence of antioxidants inhibits the formation of free radicals to delay or disable the start of initiation or propagation of the chain reaction. Below is a typical initiation stage of a system RH, a free radical R* formed as a result of the abstraction of a hydrogen atom H*.

$$RH\to \mathrm{R}\ast +\mathrm{H}\ast$$E1

$$\mathrm{R}\ast \to \mathrm{R}\ast +{\mathrm{O}}_2\to ROO\ast$$E2

$$2\mathrm{ROOH}\to ROO\ast +RO\ast +{\mathrm{H}}_2\mathrm{O}$$E3

The propagation of free radical chain reaction is occasioned by the ability of free radicals or the reactive species to react with a molecule of oxygen from the environment, resulting in the formation of peroxides and peroxy radical ROO* in the propagation stage [8] shown below. Also, the presence of antioxidants frustrates the intermediates from propagating free radicals, which according to Brewer [19] and Atta et al. [7] could be by the donation of hydrogen from the antioxidants. The propagation stage is represented below.

$$\mathrm{R}\ast +{\mathrm{O}}_2\to ROO\ast$$E4

$$ROO\ast +RH\to \mathrm{ROOH}+\mathrm{R}\ast$$E5

$$RO\ast +RH\to ROH+\mathrm{R}$$E6

In the terminal stage shown below, either two free radicals combine to form a stabilized or nonradical species or the antioxidants donate hydrogen atom (H*) to radicals to terminate the chain reaction. Brewer [19] stated that the free radicals of antioxidants may then form a stable peroxy-antioxidant compound.

$$\mathrm{R}\ast +\mathrm{R}\ast \to \mathrm{R}+\mathrm{R}$$E7

$$\mathrm{R}\ast +ROO\ast \to \mathrm{ROOR}$$E8

$$ROO\ast +ROO\ast \to \mathrm{ROOR}+{\mathrm{O}}_2$$E9

$$\mathrm{Antioxidants}+{\mathrm{O}}_2\to \mathrm{Oxidized}\mathrm{antioxidants}$$E10

Although based on the mode of production antioxidants are majorly classified into natural and synthetic antioxidants, the cellular level as the targeted site of free radicals’ damage and defensive approach of antioxidants, was also mentioned by Anwar et al. [25] as a criterion for further classifying the antioxidants into enzymatic and nonenzymatic ones. However, the classification reported by Kebede and Admassu [8], Akbarirad et al. [26] and Anbudhasan et al. [14] highlighted the mode of the provision of antioxidants to the body system; and mentioned exogenous, endogenous, and dietary antioxidants, as classes of antioxidants, subsumes the forgoing classification. Lastly, classification based on the course of action was equally mentioned by Manessis et al. [27] in their report on the classification of antioxidants. Some of them will be discussed briefly.

2.1 Natural antioxidants

Natural antioxidants are, at times, considered as extra nutritional components that occur in small quantities in food materials, especially if such food materials contain compounds like vitamins C or E that dually serve as providers of nutrients and bioactive compounds. Grozea [28] stated that they are found in natural sources, such as fruits, vegetables, and meats. They are also found in all plants parts like nuts, seeds, leaves, roots, and barks [26]. Table 1 shows some natural antioxidants that are increasingly applied in food systems. Though natural antioxidants are products of animals, plants, mushrooms, and algae. Kebede and Admassu [8] reported that natural antioxidants that are mainly used in the food system are mostly synthesized by plants (e.g. vitamins and other naturally occurring chemical compounds in food). Yadav et al. [30] corroborated with the foregoing and mentioned antioxidants commonly found in everyday foods to include vitamin C (ascorbic acid), vitamin E (tocopherols), vitamin A (carotenoids), various polyphenols including flavonoids, anthocyanins, lycopene (a type of carotenoid), and coenzyme Q10, also known as Ubiquitin, which is a type of protein. Some of these antioxidants and others highlighted in Table 1 are significantly sourced from plant-based foods. Natural antioxidants are found in most fresh foods [14]; with fruits, vegetables, and medicinal herbs being the richest sources of antioxidant compounds such as vitamins A, C, and E, ß-carotene, and important minerals [31]. Mohdali [32] reported different variations in phenolic contents not only among different fruits or vegetables but also reports of different authors even for the same fruits or vegetables. Also, two major groups, enzymatic antioxidants and non-enzymatic antioxidants constitute the human antioxidant [33, 34].

Exogenous antioxidants	Dietary sources
Vitamin C (ascorbic acid/ascorbate)	Bell peppers, strawberries, kiwi, Brussels sprout, broccoli, most fruits (particularly citrus fruits), some vegetables, tomatoes.
Vitamin E (tocopherol, tocotrienols)	Vegetable oil (olive, sunflower, safflower) and its derivatives (margarine, salad dressing, nuts and seeds, cereal grains, broccoli, Brussels sprouts, cauliflower, almonds, hazelnuts
Carotenoids(carotene, zeaxanthin, lutein, lycopene, β-cryptoxanthin, etc.)	Orange and red vegetables and fruits (carrots, tomatoes, apricots, plums) and green leafy vegetables (spinach and kale), dark leafy vegetables, sweet potatoes, yams, citrus fruits, kale, papaya
Polyphenols (flavonols, flavanols, catechins, anthocyanins, isoflavones, phenolic acids	Fruits (apples, berries, grapes, citrus), vegetables (celery, kale, onions, lettuce, eggplants, peppers, cruciferous vegetables, onions) legumes (beans, soybeans, nuts), wine, tea, cocoa, oilseeds, black tea
Trace elements(selenium, zinc)	Seafood, red meat, chicken, and whole grains

Table 1.

Some dietary antioxidants and examples of their sources.

Sources: Da Costa et al. [29] and Kebede and Admassu [8].

2.2 Dietary antioxidants

Dietary antioxidants are a complex mixture of micronutrients and bioactive phytochemicals in the diets that exhibit a range of antioxidant functions, and also according to Da Costa et al. [29], play an important role in the defense against stress. They are sufficiently supplied to the body system by the consumption of balanced diets, fruits, and vegetable-based diets. Hence, they are as well, part of exogenous antioxidants. Young et al. [35] indicated that the members of the Food and Nutrition Board of the National Research Council in the United States, described dietary antioxidants as components of food that significantly mitigate the adverse effects of reactive oxygen species and reactive nitrogen species in normal physiologic function in humans. And typical dietary antioxidants are ascorbate, tocopherols, carotenoids, and bioactive plant phenols. The potential of fruits and vegetables to promote human health, according to the literature, is due to the presence of antioxidant inclined vitamins, and the large number of phytochemicals having antioxidant properties. The most widely studied dietary antioxidants, according to Yadav et al. [30], are Vitamin C, vitamin E, ß-carotene, and other carotenoids and oxycarotenoids, e.g., lycopene and lutein. They have the potential, to reduce reactive oxygen species and reactive nitrogen species and their associated adverse effects on the body [36]. Dietary antioxidants, at times, referred to as exogenous antioxidants are derived from food eaten to complement or strengthen the activities of the endogenous antioxidants. Hence, they are either sourced from synthetic antioxidants or natural ones. Percival [37] mentioned vitamins, flavonoids, anthocyanins, and some mineral compounds as some of the naturally sourced dietary antioxidants. Table 1 highlights some of these antioxidants and their sources. Yadav et al. [30] reported that there is an increasing interest in the application of antioxidants as food preservatives, particularly dietary antioxidants intended to prevent the presumed deleterious effects of free radicals in the human body, as well as the deterioration of fats and other constituents of foodstuffs. The report of Sardarodiyan and Sani [2] indicated that vitamins C and E, carotenoids, stilbenes, phenolic acids such as benzoic and hydroxybenzoic acids, cinnamic and hydroxycinnamic acid derivatives and flavonoids—flavonols, flavones, flavanones, flavanols, flavones, and anthocyanidins (as the aglycones of anthocyanins) and others are the main dietary antioxidants. Table 1 indicates that trace elements such as selenium and zinc usually sourced from seafood, meat, and whole grains; are part of exogenous antioxidants. Although, synthetic antioxidants are not among the dietary antioxidants in Table 1, Butylated hydroxyanisole (BHA) and BHT (butylated hydroxytoluane that are frequently applied as food preservatives are examples of exogenous antioxidants (see Table 1). They are not deliberately added as food ingredients but are used as preservatives, hence are involuntarily consumed with foods and are observed to play some roles in the body system.

2.3 Synthetic antioxidants

Synthetic antioxidants are synthesized artificially by combinations of some chemical substances in the laboratory. They are widely used as food additives to prevent rancidification, owing to their high performance and wide availability [14]. They are chemically synthesized compounds since they do not occur in nature and are added to food as preservatives to help prevent lipid oxidation [7]. The instability of the natural antioxidants occasioned their involvement as preservatives for food products. According to the literature, the predominant applications of synthetic antioxidants as food preservatives are due to their high reactivity and more efficiency and effectiveness in preserving foods. Butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) were originally developed to protect petroleum from oxidative gumming [38]. However, these compounds have been used as antioxidants in human foods since 1954 and are perhaps the most common antioxidants used in those foods today [39]. Though they are predominantly used, the food industry is pushing for their replacement with natural antioxidants because of the consumers’ increasing preference for natural antioxidants which in addition, not only are more affordable but are eco-friendly. However, their usage is regulated by the established authorities to protect food consumers like the Nigerian Food and Drugs Administration (NAFDAC) and Standard Organization of Nigeria (SON), Food and Drug Administration (FDA) of the USA, European Food Safety Agency etc. Rashmi et al. [40] reported that the level of antioxidants permitted for use in food is usually determined by the fat content of the recipient food item, and is limited to 0.02% total antioxidants. Table 2 shows synthetic antioxidants commonly used as food preservatives and their recommended levels of usage, based on the legislations of FDA, European Food Safety Agency (EFSA), Joint FAO/WHO Expert Committee on food additives etc (Table 2).

Compound name	Limit in foods	Morphology/solubility	Food matrix
BHA (butylated hydroxyanisole)	< 200 mg/kg*	White waxy flakes, soluble in fat, insoluble in water	Cereals, chewing gum, potato chips, vegetable oils, biscuits, cakes pastries, sugar honey, meat products, spices, milk products, etc
BHT (butylated hydroxytoluane	< 100 mg/kg*	White crystalline compound /soluble in fat, insoluble in water	Vegetable oil, meat products, potato sticks, chicken soup base, chewing gum, sugar, honey, spices, milk products, etc.
PG (Propyl Gallate)	< 200 mg/kg*	White crystalline powder sparingly soluble in water	Vegetable oil, meat products, potato sticks, chicken soup base, chewing gum, sugar, honey, spices, milk products, etc.
OG (Octyl Gallate)	< 200 mg/kg*	White to creamy white crystalline solid, insoluble in water	Oils and fats, cereals, snack foods, dairy produce, sugar, honey, meat products, etc
DG (Dodecyl Gallate)	< 200 mg/kg*	White to creamy white Crystalline solid, insoluble in water	Oils and fats, cereals, snack foods, dairy produce, meat products, etc.
EDTA	75ppm**	Slowly soluble in water	Salad dressing, margarine, sandwich spreads, mayonnaise, processed fruits and vegetables, canned shellfish, soft drinks
TBHQ (tertiary butylhydroquinone)	120 mg/kg*	Beige colored powder, soluble in fats	Milk, milk products like cheese, meat and meat products, chewing gum, fish & Fish products, sea food, sugar, honey, spices, etc.

Table 2.

Typical synthetic antioxidants used as preservatives, their legal limits in the foods.

*

CODEX Alimentarius/Joint FAO/WHO Expert Committee on food additives.

**

US FDA.

Source: Rashmi et al. [40].

2.4 Action-oriented classification

Manessis et al. [27] further classified antioxidants based on the way they act in the biological system into the following; (i) primary antioxidants, (ii) oxygen scavengers, (iii) secondary antioxidants, (iv) enzymatic antioxidants, and (v) chelating agents. According to them, primary antioxidants donate electron or hydrogen to terminate free-radical chain reactions and some antioxidants in this group include phenolic compounds, tocopherols; and synthetic antioxidants such as alkyl gallates, BHA, BHQ , and TBHQ; (ii) oxygen scavengers are groups of antioxidants that remove oxygen to reduce their chance of furthering oxidative activities and they include vitamin C, ascorbyl palmitate, erythorbic acid, and its sodium salt; (iii) secondary antioxidants are group of antioxidants that breakdown lipid hydroperoxides into stable end-products such as dilauryl thiodipropionate and thiodipropionic acid; (iv) enzymatic antioxidants act by removing oxygen like glucose oxidase and removing ROS by such enzymes like superoxide dismutase, catalase etc. and (v) chelating agents act to remove metallic ions like iron and copper, known to catalyze lipid oxidation. Common chelating agents, according to, Pokorný [41] and Hudson [42] are citric acid, ethylenediaminetetraacetic acid (EDTA), and amino acids.

3. Effectiveness of natural and synthetic antioxidants

Antioxidants, depending on the category they belong, differ in their delivery or operation in checkmating undesirable oxidation and their derivatives to mitigate food deterioration. Variation in effectiveness of antioxidants is connected with several factors which include the system of operation, type or the group the antioxidant belongs to, aspect of functionality etc. The literature mentioned the use of antioxidants as food preservatives, and the differences in potency observed between synthetic and natural antioxidants. For instance, Rasmi and Disha [40] reported the differences in the potency of natural and synthetic antioxidants as food preservatives and stated how both differ in performance levels. The ascertainment of performance levels of both synthetic and natural antioxidants, according to Rasmi and Disha [40], depending on the number of peroxides formed in lipids over time and what they referred to as carry-through properties i.e. the ability of the antioxidant to provide stability under different processing conditions like heat (such as frying or baking), varying solubility, etc. According to the literature, the application of antioxidants as food preservatives depend on the nature or class of food being preserved and overall price consideration. For instance, preservation of foods with high rancidity levels is better achieved by using synthetic antioxidants since these are more potent and hence, have high-performance levels, while natural antioxidants with lower potency and performance levels can suffice for hydrogenated oils with lower rancidity levels [3]. However, the effectiveness of antioxidants may be measured based on the extent to their utilization promotes food safety, in terms of promoting the health of the consumers, with respect to disabling occurrences of degenerative diseases in vivo, and in terms of preventing or minimizing lipid peroxidation which produces toxic compounds that enhance deterioration of flavor, color, texture, and nutritional values [43] which incidentally lead to overall depreciation of food quality and its consumer acceptability [44]. Also, studies carried out on the applications of natural antioxidants, according to Fernades et al. [45] showed their promotion of the palatability of food products, that is, the appetizingness of such products. The effectiveness of natural antioxidants in stabilizing food products in a manner equivalent to that of synthetic antioxidants and their contribution to longer shelf-life to meat products was, as well, reported by Jung et al. [46]. The strong correlation between diet and disease prevention instigated by applications of antioxidants in the food system which pushes industrial trend toward the development of functional food products [47] is leading to increasing adoption of many dietary and technological techniques that facilitate the use of these antioxidants in maintaining the quality of food products like meat and its derivatives [45]. The type of such technological strategy was reported by Velasco and Williams [48] to be the inclusion of plant ingredients having high bioactive potential in packaging materials or incorporation of dietary supplements in animal feeds. Hence, whereas synthetic antioxidants are considered to be more potent or effective as preservatives because of their readiness to donate electrons to food substrates, the increasing preference of consumers to natural antioxidants and the associated inclination of the food industry to satisfy the consumers’ demands; is factored on the following: their good bioactive health potential, their perceived functional properties and increasing demand for healthy food products.

Also, in terms of the involvement of food in promoting the consumers’ health, food processors are increasingly producing food products containing prerequisite antioxidants (natural ones) to discourage the high incidence of degenerative diseases and improve food safety. Voutilainen [49] reported the important role nutrition play in preventing many chronic diseases such as cardiovascular diseases (CVD), cancers, and degenerative brain diseases. This assertion was corroborated by Atta et al. [7] who stated that consumption of dietary antioxidants such as β-Carotene prevents muscular degeneration and cataracts. The potency of natural antioxidants in this regard overrides that of synthetic antioxidants. The overriding contributions of natural antioxidants in checkmating occurrences of lifestyle diseases aforementioned are well reported in the literature. Though the use of synthetic antioxidants in maintaining the quality of ready-to-food products has gained prominence, the increasing demand for food products that guarantee the safety of consumers has instigated the food industry to seek their replacement with natural antioxidants [50]. According to Anbudhasan et al. [14], food products containing natural antioxidants were more functional in promoting shelf-life and health of their consumers when compared with those ones whose antioxidants were removed during processing. The above reports indicated that natural antioxidants are the kernels of involvement of foods in minimizing chronic diseases, promoting health and incidentally reducing intake of drugs taken for healing, which also generate adverse side effects. Whereas synthetic antioxidants have the advantages of being readily available and affordable and are more reactive when compared with natural antioxidants, the preference of consumers for food products processed with natural antioxidants, is increasingly demeaning their applications as food preservatives.

4. The uses of antioxidants in food systems

Antioxidants are part of food additives used in the food systems primarily to infringe oxidation of lipids and proteins to elongate the keeping quality of food products, thus enhancing the shelf-life of food products. Antioxidant compounds present in food systems help to reduce the number of lifestyle diseases which may reduce the amount of drugs consumed by people who suffer from these diseases. Atta et al. [7] agreed with the above assertion with a report that antioxidants are widely used as an ingredient in a dietary supplement for promoting good health. Recent developments in food processing are indicating that food could be used as preventive and curative channels to discourage increasing occurrences of chronic diseases such as cardiovascular diseases, high blood pressure, diabetes, cancers etc. being witnessed among people. This may enliven the intention of replacing synthetic antioxidants with natural ones that have the potential to elongate food quality and enhance the health of food consumers. The use of antioxidants as a preservative and in enhancing the flavor, aroma, and color of food products is reported in the literature [8]. The addition of antioxidants to food items as preservatives can be during many different stages of food production [51], but since the antioxidants have no potential to reverse already oxidized food products; their application during the early stage of the manufacturing process may give better results. Some practical applications of antioxidants in the food system include their addition to fats and oils used in food production [14], in the preservations of vegetables and vegetable products; fruits and fruit products [52]; cereals and bakery products; milk and milk products like cheese; meat, fish and their products; spices; and other dry foods like sugar, honey, beverages, and chewing gum [53].

Also, apart from being used as preservatives, antioxidants could be utilized to enhance the benefits of food to man. Aside from the provision of nutrients, the inclusions of antioxidants or the use of antioxidant-containing ingredients in food processing improve the productivity of food processing and its products. Their use could bring about an added value to food products by giving them the potential to provide nutrients and bioactive compounds and hence, promote the tendency of food consumed to checkmate lifestyle diseases and intake of drugs occasioned by occurrences of the diseases.

The use of antioxidants in food systems is bringing up novel food products designed to take care of both the nutritional and health aspects of human life. Before now, food products were produced to provide mainly nutritional needs of the consumers with little or no attention given to using food to address the increasing occurrence of degenerative diseases and to incidentally discourage the intake of drugs because of their associated side effects.

Also, the reports of the literature have indicated that the inclusion of plants parts with a high concentration of antioxidants is more effective than the use of extracted antioxidants as food supplements, either in terms of prolongation of shelf-life or particularly of promoting health orientations of food products in the food system [54]. Anbudhasan et al. [14] corroborated the foregoing by implying that processing impacts negatively on the potency of the antioxidants. And incidentally, the literature is replete with information that most antioxidants are concentrated in the areas of plants, like the seed/seed-coat, peels, etc. as in mango fruits; usually generated as wastes/byproducts discarded as pollutants to the environment by processing operations. Kebede and Admassu [8] confirmed this assertion by stating that wastes and by-products of fruits and vegetables in the food processing industry are abundant sources of antioxidant polyphenols or phenolic compounds. This means reintegration of these components as constituents of the food system could boost the strength of food in providing required antioxidants. The exploration of antioxidants may, therefore, likely reduce the quantity of wastes/by-products generated to promote eco-friendly food processing. Some studies have already been done on by-products, which could be potential sources of antioxidants [32]. Agricultural and industrial residues are attractive sources of natural antioxidants [55]. The use of waste as a source of polyphenols and antioxidants may have considerable economic benefits to food processing industries. Therefore, a cheap, efficient, and environmentally sound utilization of these huge agro-industrial wastes is needed [56].

The use of antioxidants in the food system depends on the conditions of food processing operations applied. According to Reddy et al. [57], processing (including preparation) of food is designed to make food healthier, safer, tastier, and more shelf-stable. This is achieved by inactivating disease-causing microorganisms (pathogens) and enzymes to reduce moisture content and concentrate nutrients and bioactive compounds in processed foods, or to soften the outer tissue to separate fruit/vegetable skin [58]. This incidentally causes several changes including appearance, composition, nutrition, and sensory properties which occur during processing in terms of color, texture, and flavor. Generally, food-processing procedures are recognized as one of the major factors responsible for the destruction or changes of natural phytochemicals, which may affect the antioxidant capacity in foods [59]. Processing conditions either boost nutrients and antioxidants or reduce them depending on many factors. The conditions that are generally considered in food processing include temperature, time, the level of antioxidants in the ingredients/raw material; but for antioxidants, it is reported that genetics, environment, growing conditions (moisture, fertilization, pests, and disease burden, etc.) of the fruits and vegetables from which they are extracted, as well as processing methods and storage conditions affect the level of antioxidant activity of phytochemicals [60, 61, 62]. The understanding that over-processing or some severe processing conditions and environment could eliminate most of the antioxidants are inducing processors to explore processing techniques capable of producing food products containing assured levels of nutrients and antioxidants. One of the techniques, as shown by the recent development in food processing, is the enclosure or entrapment of antioxidants within a material or substance reported in the literature as encapsulation technology. Trifkovic et al. [63] reported on different encapsulation technologies applicable in food processing for antioxidants to include spray drying, spray chilling, spray cooling spray-drying, spray-chilling, spray-cooling, melt injection, fluidized bed coating etc. Encapsulation according to Pattnaik et al. [64], protects sensitive antioxidants from being destabilized by severe processing conditions or environment, improves their bioavailability, masks their identifiable astringent flavors, enhances their delivery in active forms to the targeted site or appropriate release in the gastrointestinal tracts.

Furthermore, apart from the use of encapsulation technology for the retention of nutrients and antioxidants in food products, the interplay of processing conditions is another way to optimize the availability of nutrients and antioxidants. Nayak et al. [58] reported that the application of kinetic models in the thermal processing of foods is important to assessing and predicting the influence of processing operations on critical quality parameters to minimize the undesirable changes and to optimize the quality of specific foods. Thus foods could be processed to provide the required nutrients and antioxidants.

5. Implications of replacing synthetic antioxidants with the natural ones in food systems

Food being one of the basic needs of man must always be available as and when needed at an acceptable condition or quality. This means preserving natural or processed food products, ensuring retention of the characteristics of the foods that constitute acceptable quality to consumers. The application of antioxidants in the food system was widely reported in the literature to checkmate undesirable oxidative reactions, identified as one of the major causatives of food deterioration; in order to maintain the quality of foods. Antioxidants have become an indispensable group of food additives mainly because of their unique properties of extending the shelf-life of food products without leaving any adverse effect on their sensory or nutritional qualities [2]. Atta et al. [7] also, reported the use of antioxidants to prevent the oxidation process in foods which leads to rancidity and browning. The major segment of antioxidants, natural and synthetic antioxidants, are involved as ingredients in food systems, mainly as preservatives and then recently as the promoter of health orientation of foods. Anbudhassan et al. [14] mentioned the involvement of both aspects of antioxidants, especially the recent drastic increase in the application of natural antioxidants at the expense of synthetic ones in the food system, because of concern for the safety of food consumers. Before now, synthetic antioxidants were highly involved in the food system because they were adjudged to be more reactive and effective as food preservers than natural ones. While the use of synthetic antioxidants (such as butylated hydroxytoluene and butylated hydroxyanisole) to maintain the quality of ready-to-eat food products has become commonplace, consumer concern regarding their safety has motivated the food industry to increasingly apply more natural antioxidants [50].

Thus, the friendliness of natural antioxidants, in comparison to synthetic ones, to the body system could be the reason for increasing interest in replacing synthetic with natural antioxidants, as food preservers, in food systems. Though Anbudhassan et al. [14] reported that synthetic antioxidants are widely used as food additives to prevent rancidification, owing to their high performance and wide availability, the public opinion that natural compounds are safer and more health-beneficial per se, has motivated the meat industry, for instance, to exploit plant-derived additives in meat systems with the objective of replacing synthetic antioxidants [65]. Whereas the literature is replete with increasing replacement of natural antioxidants with synthetic ones, it is necessary to elucidate implications of this in the food system. The increasing use of natural antioxidants will promote health orientation of foods, bring up new food products, enhance food quality, promote processing of composite food product, improve safety with assured attainment of food security, improve the circular economy of nations that invest in it, ameliorate occurrences of chronic diseases and their associated reduction in drug intake and many other benefits that are discussed hereunder.

5.1 Promotion of health orientation of food

Food is an indispensable resource to a man taken to provide nutrients required for the growth of the body cells with little or no consideration for its inclination to health aspects of life. The recent development in the food systems which targets the use of food to prevent chronic diseases as afore-mentioned seem to be widening the scope of benefits uses or productivity of food to man. In recent years, considerable research has been carried out, evaluating natural substances as antioxidative additives in food products, leading to novel combinations of antioxidants and the development of novel food products. The natural antioxidants have, in addition, shown a supportive effect to the human body with documented health benefits [8]. The targets of food processors, in the recent development, are to provide food products made up of required nutrients and antioxidants to ensure that foods have added value of promoting health of the consumers [66]. Antioxidants have important preventive roles not only on undesirable changes in the flavor and nutritional quality of food but also on tissue damage in various human diseases [8]. They are potentially effective in the prevention of degenerative illnesses, such as different types of cancers, cardiovascular and neurological diseases, cataracts, and oxidative stress dysfunctions [67, 68]. Chronic diseases such as arteriosclerosis and cancer, which are the leading causes of death in the Western world, are likely to be mediated by free radical and lipid peroxidation mechanisms [69], but could be remedied with increasing consumption of dietary antioxidants processed into food products. Antioxidants have been investigated and reported to play a specific role in the prevention of these diseases/disorders [68]. In the last decades, several epidemiological studies have shown that dietary intake of foods rich in natural antioxidants was correlated with a reduced risk of coronary heart disease [70, 71]. Dietary and natural antioxidants present in foods and other biological materials have attracted considerable interest because of their presumed safety and potential nutritional and therapeutic or health effects [72, 73]. While processing food to provide required nutrients, food processors should also consider other health-related aspects of their additives and products. The quality parameters for acceptance of food should widen to include adequate availability of antioxidants in addition to those characteristics for which food quality is measured.

5.2 Production of novel food products

The attempt to include the required availability of antioxidants in food as a measure of food quality characteristics is undoubtedly throwing up a novel or new products in food systems globally. Kedebe and Admassu [8] reported changes in human lifestyle and his view of food which are occasioning shift from one nature of food to another, e.g. from convenient foods to ready to eat food products category. The deadliness of chronic diseases and the understanding that consumption of the right foods could prevent or end their occurrences may broaden the demands of consumers of inclusion of antioxidants at the required levels in food products. In a bid to meet this dynamic demands of consumers, food processors are increasingly developing new food products processed to provide nutritive and healthy values to consumers.

5.3 Enhancing food quality

The contributions of antioxidants to the enhancement of food quality are well reported in the literature. Anbudhassan et al. [14] mentioned the involvement of antioxidants, both natural and synthetic in accentuating the shelf-life and appearance of many food products to buttress the disposition of antioxidants toward promoting food quality. While the use of synthetic antioxidants (such as butylated hydroxytoluene and butylated hydroxyanisole) to maintain the quality of ready-to-eat food products has become commonplace, consumer concern regarding their safety has motivated the food industry to seek natural antioxidants [50]. The antioxidants obtained from plants are more functional toward improving the shelf life of food products and providing healthier promotion when compared to materials whose antioxidants have been removed during processing [14]. Orientating foods toward promoting the health of consumers, in addition to their nutritional roles emphasizes the widening contributions of natural antioxidants to the maintenance of food quality. Kebede and Admassu [8] alluded to the effectiveness of natural antioxidants in preventing undesirable changes in the flavor and nutritional quality of food and tissue damage that occasion incidence of various human diseases; and asserted that nutritional importance, promotion of health, and prevention against damages caused by free radicals can lead to the potential applications of antioxidants in food industries in more intensified approaches. The applications of natural antioxidants in the food system will undoubtedly improve keeping quality of foods in the food systems. This is in agreement with reports of Arshiya et al. [50] and Singh et al. [68] on natural antioxidants such as vitamins (ascorbic acid [AA] and α-tocopherol (E306)), many herbs and spices (rosemary, thyme, oregano, sage, basil, pepper, clove, cinnamon, and nutmeg), and plant extracts (tea and grape seed) applied on meat products as preservatives. The supremacy of natural antioxidants over synthetic ones in the functionality of antioxidants as enhancers or enablers of increasing shelf-life of foods is indeed incontrovertible as attested to with the report of Kebede and Admassu [8], which stated that the antioxidants obtained from plants are more functional toward improving the shelf life of food products and providing health promotion.

5.4 Promotion of circular economy

The increasing applications of natural antioxidants will incidentally boost or signify a circular economy since most the antioxidants are derived from by-products/wastes generated during food processing or utilization. The literature is replete with the involvement of food by-products or wastes in the extractions of natural antioxidants or their recycling for their use as ingredients in the processing of some foods. Bartosz et al. [74] associated the use of food by-products/wastes as raw materials in the production and or commercialization of natural antioxidants as well as in the advancement of the circular economy. The circular economy is a regenerative system that, unlike the linear economy, involves recycling or reuse of wastes generated in the food system to boost values derivable from the food processing system. The circular economy is all about minimizing waste generation in the food system by the re-use of food, conversion of by-products, and wastes into usable products, recycling nutrients, and adopting changes in diet toward more diverse and more efficient food patterns [75]. The identification of food wastes as reservoirs of antioxidants, and increasing inclination to eco-friendly food processing culture will purvey strategies and projects required to encourage upstream waste recovery, leading to the production of downstream value-added ingredients (e.g. natural antioxidants), based on a sustainable economy, i.e. circular economy. In the concept of a circular economy, recovery and valorization of wastes allow materials to be reused and be recycled into the supply chain, allowing economic growth from environmental losses [76]. Thus increase in applications of natural antioxidants will incidentally translate to an increase in the utilization of food wastes or adoption of eco-friendliness in food processing, the purveyor of the sustainable or circular economy.

6. Conclusion

Antioxidants are substances that minimize or disable oxidative activities in food and body systems to preserve them from being damaged. Two major types of antioxidants, based on their mode of synthesis applicable in the food system for food preservation are natural and synthetic antioxidants. Though synthetic antioxidants, from the inception of food processing, are predominantly used as food preservatives to maintain the keeping quality and appearance of many foodstuffs; some reports about their carcinogenicity and mutagenicity and hence, the concern of consumers’ health have motivated the food industry to seek for their replacement with natural antioxidants. The replacement is necessary because of the increasing demands of consumers for health-promoting foods globally. The use of natural antioxidants, either in the form of extracts and or parts of natural resources that contain concentrations of antioxidants; in food processing and preservation, may encourage consumption of healthy foods. Also, the discovery that natural antioxidants are mostly concentrated in the parts of raw resources usually removed as wastes during food processing and, the efforts to reintegrate the wastes into the food system, seemingly included promotion of eco-friendly food processing and a guaranteed sustainable/circular economy; as one of the implications of replacing synthetic antioxidants with natural ones in the food system. The use of plant parts, as food ingredients instead of extracted antioxidants as food supplements, heightens the effectiveness of natural antioxidants in the food system either in terms of prolonging shelf-life or promoting health orientations of food products. The replacement of synthetic antioxidants with natural ones will, thus, boost sensory, safety, and other quality parameters as well as health orientations of food products and incidentally, the values of food to man.