Dietary Antioxidants and Bioactive Compounds in Food Processing

Abstract

The antioxidants available in fresh organic materials could vary significantly from all those we consume through diet, as it has historically been recognized. Plants contain several phytochemicals, which possess strong antioxidant activities. A large variety of phytochemicals have been isolated and characterized from familiar sources, including vegetables, such as onion and broccoli; fruits, such as apples and grapes; spices, such as nutmeg, pepper, and turmeric; and brews, such as green tea, oolong tea, and red wine; which possess strong antioxidant properties. This is typically affected by the usage of thermal and nonthermal food processing methods. This chapter deals with various traditional and unconventional techniques that can be utilized to recover bioactive constituents. Any traditional method’s extraction effectiveness is primarily influenced by the solvents utilized. Among the most effective approaches, notably pressurized solvent extraction, supercritical fluid extraction, pressurized low-polarity water extraction, enzyme-assisted extraction, pulsed electric field extraction, ultrasound-assisted extraction, and microwave-assisted extraction were reviewed. The contrasting antioxidant activities of various extraction techniques were emphasized, as well as the processing techniques and industrial applications for unconventional ways of antioxidant extraction. How well this varies throughout absorption, how this impacts gastrointestinal function, and subsequent accumulation into the plasma, but which in vivo biological consequences it has on the internal organs all are aspects to consider.

1. Introduction

Antioxidants are elements, which are derived from natural and chemical substances, which is having the potent ability to scavenge free radicals by losing an electron and neutralize or slowdown the autooxidation process. Several free radicals are unbalanced and extremely reactive. Antioxidants are ready to contribute to an electron either by oxidizing or reducing other molecules [1]. Also, these antioxidants are capable of preventing and inhibiting cell membrane, structural, DNA, Lipids, carbohydrates, and cellular protein damage. During our body’s metabolism and diet, it produces lighter and strong antioxidants, such as uric acid, ubiquinol, glutathione micronutrients α-tocopherol, and ascorbic acid. Even though numerous amounts of antioxidants are there in the form of macro and micronutrients, such as vitamin E, Vitamin C, and beta-carotene to scavenge free radicals [2]. Both ionizing processes and nonenzymatic reactions involving oxygen and organic molecules can lead to the form of free radicals. Few organs are internally produced by some free radicals, such as mitochondria, peroxisomes, xanthine oxidase and some pathways arachidonate, phagocytosis, reperfusion injury, and other external factors.

Fruits and vegetables are one of the best sources of antioxidants. Consuming fresh juices, pastes, and canned foods gives an enormous quantity of antioxidants to our body [3, 4]. Whatever, during food processing least number of antioxidants are loosed and hence, might impact the final product to stimulate health properties [5]. During the twentieth century, food industries introduced antioxidants to inhibit the oxidation process of packed and stored foods [6]. While the impact of antioxidants as loss and gains of bioavailability in food processing have been studied before [7]. It is very important to develop augmented approaches for the preservation of food and the development of activity and bioavailability of antioxidants. It is also used to study about significant of the functional elements of food materials that we used in our daily diet and the changes in the composition of food during processing [8]. Especially performing thermal and nonthermal processing, determining the bioavailability of dietary antioxidants level and quality of dietary antioxidants [9, 10, 11].

2. Classification of antioxidants

Generally, antioxidants are present in various foods in various forms. Those antioxidants are classified depending on their functions, mode of action, characteristics, and type of nature [12]. The known major antioxidants are natural and synthetic antioxidants (based on the type), dietary, and endogenous and exogenous antioxidants (based on the function). Furtherly it is classified as enzymatic and nonenzymatic antioxidants. The enzymatic antioxidants are catalase, glutathione, and dismutase, and nonenzymatic antioxidants are tocopherols, melatonin, ascorbic acid, vitamin E, and uric acid. These antioxidants play a very crucial role in food processing and preservation [13].

2.1 Endogenous antioxidants

The only antioxidants with the ability to synthesize their own antioxidant compounds are called an endogenous antioxidants. Further, they can be classified based on their structural characteristics as enzymatic and nonenzymatic antioxidants. The body utilizes a variety of endogenous protective mechanisms alongside dietary antioxidants to support and protect against various consequences. Those enzymes utilized nutrient cofactors copper, zinc, selenium, iron, and manganese to react with toxic intermediate oxidative complexes for maximum catalytic activity [12]. The amino acids are glycine, glutamate, and cysteine synthesized glutathione is an essential water-soluble antioxidant.

2.2 Exogenous antioxidants

Vitamins, polyphenols, carotenoids, as well as certain mineral complexes are examples of naturally occurring sources through which exogenous antioxidants could be synthesized [12]. Antioxidants are getting more prominent, particularly in those intended to avoid the anticipated adverse consequences of the existence of reactive oxygen species in the internal organs and the degeneration of additional dietary constituents, such as fats [13].

2.3 Dietary antioxidants

Ascorbate, tocopherols, carotenoids, and bioactive plant phenols are types of dietary antioxidants. The antioxidant vitamins in fruits and vegetables, some of which possess more potent antioxidant properties than others, are mainly accountable for their health benefits [14, 15, 16]. Among the most exhaustively researched dietary antioxidants include vitamins C and E, ß-carotene, other carotenoids, and oxycarotenoids, such as lycopene and lutein [13]. Vitamin C is thought to be the most significant water-soluble antioxidant in extracellular fluids. Before lipid per oxidation commences, it has the potential to remove free radicals in the aqueous environment. The most potent chain-breaking antioxidant in the cell membrane, wherever it protects cell wall fatty acids from lipid peroxidation, is vitamin E, a prominent lipid-soluble antioxidant. Vitamin C has allegedly demonstrated the ability to stimulate vitamin E [17].

It is also hypothesized that ß-carotene and certain other pigments protect lipid-rich tissues from damaging free radicals. According to studies, several vitamins and ß-carotene may enhance the other’s actions [18]. Although carotenoids seem to function as “pathogen-associated molecular enhancers” in individuals, flavonoids protect plants from either a wide range of environmental stresses. The anti-inflammatory, anti-allergic, antimicrobial, antiaging, and anti-carcinogenic characteristics of flavonoids have been demonstrated [13].

2.4 Natural antioxidants

Those oxidants known as naturally occurring antioxidants could be present in foods, including fruit and vegetables and livestock [19]. All-natural compounds, especially berries, plants, nuts, beans, branches, stems, and barks, possess antioxidant compounds [19]. Vitamin C, E, and A (ascorbic acid, tocopherols, and carotenoids), different polyphenols, comprising quercetin, proanthocyanidins, and lutein, and ubiquitin known as a coenzyme Q₁₀, a type of dietary protein, are among the most abundant vitamins in food products [13]. Plants namely the vitamins as well as other originating molecules in our food create natural antioxidants. The majority of fresh fruit and vegetable include ubiquitin, a specific type of protein, which is a potent antioxidant [20].

Living beings get all these elements mostly through plant-derived substances [11]. The excellent sources of antioxidant substances, comprising vitamins A, C, and E, ß-carotene, and essential minerals, are fruits, vegetables, and medicinal plants [21]. The total amount of phenol in various parts of plants, or even of the same vegetables and fruit varies greatly [22]. Enzymatic antioxidants and nonenzymatic oxidants make up the two main categories of the biological antioxidant system [23].

2.4.1 Enzymatic antioxidants

Both primary and secondary metabolic inhibitors are even further characterized as catalytic antioxidants. The basic protection is composed of three essential enzymes that prevent the production of free radicals or neutralize them: glutathione peroxidase, catalase, and superoxide dismutase [23]. Glutathione reductase and glucose-6-phosphate dehydrogenase are two supplementary metabolic inhibitors [24]. Even though these two enzymes really should not directly counteract free radicals, they might enhance existing endogenous inhibitors in their abilities to achieve this.

2.4.2 Nonenzymatic antioxidants

The production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) are certainly scavengers by nonenzymatic antioxidants, which include proteins (glutathione), vitamins E and C (that also inhibit the oxidative damage of cellular membrane), nitrogenous compounds, including uric acid, which inherently acts as an antioxidant against peroxynitrite in bloodstream, albumin, bilirubin, N-Acetylcysteine (NAC), and melatonin [17, 25, 26].

2.5 Synthetic antioxidants

Antioxidants that are chemically synthesized and added to perishable foods as preserves to contribute to the inhibition of peroxidation are termed synthetic antioxidants, since they cannot appear in nature [27]. Synthetic antioxidants were created in order to provide a consistent catalase activity analysis method to correlate with antioxidant properties and to be incorporated into foods. Such bioactive molecules are included in the food to enhance storability and to assist it to resist alternative treatments and environments. Consequently, synthetic antioxidants are incorporated into essentially all packaged products, which are supposedly acceptable [25]. The two most commonly used synthetic scavengers are butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA). Considering the daily allowance and effective dose for the synthesis of various inhibitors, contradictory results were obtained [14]. Moreover, mixed data exist on the influence of antioxidant compounds on people’s well-being. BHT, BHA, propyl gallate (PG), dodecyl gallate (DG), and tertiary butylhydroquinone are among the chemical additives currently authorized to be used in foods [2, 27].

3. Sources of antioxidants

The majority of natural antioxidants in use today are derived from plant sources, such as fruits, vegetables, spices, and herbs [26]. These foods are particularly rich in plant secondary metabolites, such as phenolic compounds, terpenoids, alkaloids, vitamins, and carotenoids [28].

The most popular antioxidants are the essential oils extracted from culinary spices and herbs, such as thyme, oregano, marjoram, basil, lavender, and rosemary. They have been reported to be good sources of natural antioxidant-rich molecules, but have limited applications due to their strong aroma and flavor characteristics [29, 30].

Another common source of dietary antioxidants is the brewed tea used around the world. They include non-fermented (green), semi-fermented (Oolong), aged (Pu’er), and fermented (black). Tea is very rich in polyphenols. Fresh green tea leaves have been reported to contain around 36% polyphenols, on a dry-weight basis [26]. Aqueous tea extracts are also good sources of natural antioxidants owing to a large number of metabolites, such as catechins, tannins, and other flavonoids, in a fresh brew. They have the additional advantage of not presenting a strong flavor when compared to essential oils [29].

The polyphenols in green tea have been observed to bring about programmed cell death otherwise known as apoptosis in numerous cancer cells, such as prostate, lymphoma, colon, and lung cancer cells. Black tea, on the other hand, was found to inhibit DNA synthesis while enhancing the apoptosis of benign and malignant tumor cells. The antioxidant activity of green tea catechins is normally in the order of EGCG (epigallocatechin gallate) almost equal to ECG (epicatechin gallate) activity, which is better than EGC (epigallocatechin) and greater than EC (epicatechin), while that of theaflavins of fermented teas are theaflavin digallate (TF-2) greater than theaflavin monogallate (TF-1 A & B) than theaflavin (TF). The antioxidant activity of green tea almost often surpasses that of oxidized black tea and its extracts [31].

Gallic acid is a recognized natural antioxidant that induced fragmentation of DNA in THP-1, HL-60, U-937, and ML-1; four diverse human myelogenous leukemia cell lines, but not in erythroleukemia (K- 562) cell lines and human T-cell leukemia (MOLT-4). Gallic acid was found to induce apoptosis in HL-60 RG cells through ROS (reactive oxygen species) generation, an influx of Ca2+ leading to the activation of calmodulin. The primary pigment in turmeric, curcumin, and phenolic compound was found to induce apoptosis in transformed human and rodent cells in culture. Curcumin mediates this chemopreventive action by inhibiting the formation of cyclooxygenase metabolites, which provides a mechanism for the induction of apoptosis. Quercitrin, quercetin, and kaempferol are flavonoids present widely in around 70% of all plants. Flavonoids differ notably in their antioxidative effectiveness, depending on their structure [31].

The most effective dietary antioxidants belong to the family of phenolics and polyphenolics. Phenolic compounds occurring in foods belong to the phenylpropanoid (C6-C3) family and are derivatives of cinnamic acid. These compounds are formed from phenylalanine, and to a lesser extent in some plants from tyrosine, via the action of phenylalanine lyase, or its corresponding tyrosine lyase. Edible oils and oilseeds provide a rich source of unsaponifiable matter that contains a variety of active ingredients that may be used to prevent or control deteriorative processes. The non-triacylglycerol constituents in oils and oilseeds belong primarily to the tocols (tocopherols and tocotrienols) family, phenolics and flavonoids, sterols, phospholipids, carotenoids, and triterpene alcohols as well as the phytic acid family of compounds [27]. Carotenoids play a major role in the prevention of various health disorders, such as cancer, metabolic disease, and cardiovascular diseases [32].

4. Extraction of antioxidants from natural sources

Antioxidants are isolated and purified from different parts of plants, such as roots, stems, leaves, fruits, seeds, and peels. The attributes of antioxidants from natural sources and their antioxidant potential depends not only on the quality of the extract concerning its geographic origin, nutritional aspects, and storage, but also on the methodologies used for their extraction.

The methods for analyzing antioxidants include the estimation of total antioxidant activity by electrochemical or spectrophotometric methods. The specific detection and assessment of different antioxidant molecules are facilitated by various chromatographic—TLC, HPLC, LC, GC, MS, NMR, capillary electrophoresis, and NIR methods. However, before quantification can be done, it is required to extract the different components from the food matrix. This involves technologies such as the use of organic solvents for solvent extraction, subcritical water extraction, supercritical fluids, high hydrostatic pressure, microwave procedures, pulsed electric fields, or ultrasonics.

The yield of antioxidants extracted from the plant material is affected mainly by the environment under which the process of extraction occurs. Every plant material is unique in terms of its structure and composition; therefore, the behavior of the resulting material-solvent system is unpredictable upon combining it with solvents. Assisted techniques using original fluids, which are referred to as nonconventional methods of extraction, such as supercritical fluids, supercritical water, ultrasound-assisted extraction, enzymatic-assisted extraction (EAE), microwave-assisted extraction (MAE), supercritical fluid, and pulsed electric field (PEF) have become more efficient and popular in recent times [33].

4.1 Solvent extraction

Solvent extraction is a technique that involves applying a solvent to extract or separate the desired component, called the solute from solid food material. The separation factor in solvent extraction is the chemical equilibrium that exists between the solid and solvent phases. And the concentration difference of the component between the two phases is the driving force for solvent extraction. An ideal solvent for extraction should have a high affinity for the solute being separated, it should be selective and dissolve the component of interest to a large extent while having a minimum capacity for the other undesirable components. It should be chemically stable, forming no irreversible reactions with contacting components, regenerable, and have low viscosity values for easy pumping and transportation [33].

The most efficient solvents used in extracting anthocyanins, being polar molecules, are aqueous mixtures of methanol, ethanol, and acetone. Among the most frequent solvent extraction methods are the ones that use acidified ethanol or methanol as solvents. The acids in the solvent system rupture the cell membranes and release anthocyanins. As this can cause damage to the anthocyanin structure, it is advised to acidify the solvents with organic acids, such as formic or acetic acid, rather than mineral acids, such as 0.1% HCl, to minimize damage [33].

Alcoholic solvents are used to extract antioxidant phenolic compounds from various sources. Ethanol, a polar solvent has been shown to effectively extract several secondary metabolites, including flavonoids, catechol, glycosides, and tannins, from raw plant materials. It is also to be noted that in food processing industries, ethanol is preferred over methanol due to its inherent toxicity. Lycopene, a fat-soluble antioxidant present in large quantities in tomatoes, is extracted with organic solvents, such as benzene, acetone, petroleum ether, ethanol, hexane, and chloroform.

4.2 Extraction using supercritical fluids

Extraction with the help of supercritical fluids (SCF) has gained popularity in the food processing domain. Similar to conventional solvent extraction, SCF extractions use fluids in their supercritical states, which have desirable transport properties that enhance their potential as solvents for extraction processes [34]. CO₂ is one such example that is nontoxic, noninflammable, and requires only a bare minimum amount of solvent for the process. Extraction is quicker, takes about 10–60 min, is selective, and requires only small quantities of sample and no additional cleanup. An improvement over this method is the use of enhanced solvent extraction, which uses carbon dioxide, organic solvents, or water at high temperatures and pressure. SCF extraction has been used successfully for extracting anthocyanins and polyphenols from grapes, wine, and some herbs [34].

4.3 Ultrasonics

Ultrasonics is one of the commonly used techniques in the food and beverage industry, which enhances the mass-transfer phenomena. It has been successfully applied for extracting anthocyanins, polyphenols, and flavonoids from various plant sources.

4.4 Microwave-assisted extraction (MAE)

Microwave-assisted extraction (MAE) helps reduce the time needed for extraction and the quantity of solvent used. MAE involves extraction under controlled conditions of temperature and pressure with or without the addition of a solvent. It has been reported that using closed vessels cuts down the extraction time and increases the efficiency of extraction. MAE has been used to extract phenolics in a very effective manner [35]. Recent advances in this domain include microwave hydrodiffusion and gravity (MHG) and solvent-free microwave extraction (SFME).

4.5 Subcritical water extraction (SWE)

Subcritical water extraction uses subcritical water or pressurized hot water below the critical pressure of 22 MPa to extract natural compounds from herbs, plants, and food materials, such as pomegranate seed residues, red grapes, potato, and citrus peels [8].

4.6 High hydrostatic pressure (HHP)

High hydrostatic pressure (HHP) works by improving mass transfer rates, thereby increasing cell permeability and secondary metabolite diffusion by changes in phase transitions. HPP has been reported to be utilized in extracting anthocyanins and polyphenols from grapes, red fruits, and grape skins [35].

4.7 Enzyme-assisted extraction (EAE)

Enzyme-assisted extraction (EAE) has been used efficiently to release and recover bioactive molecules from several algal and plant sources, such as lemon balm, red algae, alfalfa, and pumpkins. Enzymes are capable of catalyzing the degradation of plant cell walls, thereby releasing the bioactive compounds stored inside the cells. Examples of enzymes used for this procedure are cellulases, hemicellulases, pectinases, etc. [35].

Other major techniques, such as pulsed electric fields and high voltage electrical discharges, are also gaining popularity as noninvasive techniques to extract secondary metabolites from plant sources.

5. Processing of antioxidants

Despite the knowledge that there are numerous antioxidants in nature, typically just a few amounts of basic ingredients, especially vegetable fatty acids and oils and rosemary leaves, are utilized to synthesize extracts with antioxidant potential [31]. Considering these substances have enough potential to cause serious harm, cytotoxic, or neurotoxic to people, the desire for bioactive components has resulted in a reduction in their utilization [15]. It is, therefore, argued that synthetic substances, such as BHT, are hazardous for ingestion when used in therapeutics because they could have negative health consequences for humans [34]. The unfavorable effects of antioxidant compounds on well-being have been significantly reduced through investigation.

The amount of production of natural antioxidants from waste vegetables and other fruits has generated a significant amount of attention. Huge quantities of waste products, particularly peels and nuts, are generated during the process of processing fruits, vegetables, and grains [34]. Regulatory constraints mean handling these substances is a challenge that is already complex. As a result, unique perspectives on utilizing these materials as by-products for further utilization on the development of additives or supplement with high amounts of nutrients have drawn increasing attention considering that these are greater commodities and their recovery may be economically feasible. According to the original source, the production of fruit and vegetables and oilseeds generates different quantities of by-product (Table 1) [17].

By-products	Amount of phenol
Onion peel	105 g/kg
Orange peel	1.8 g/kg
Lemon peel	13.3 g/kg
Grape peel	13.8 g/kg
Potato peel	7.8 g/kg
Apple peel	2.4 g/kg

Table 1.

Antioxidant amounts in different by-products.

6. Antioxidant composition varies during food processing

Consumption of natural antioxidant compounds from food products that are already abundant in all of these bioactive substances [36]. Although food processing is proven that it has a significant impact on nutritional properties and pharmacological activities [31]. Food processing involves both thermal and nonthermal procedures, including storing, sorting, washing, packaging, and transportation, to produce the desired final product [18]. Antioxidants are lost during the processing of fruits and vegetables, and processed foods have significantly lower bioavailability when compared to fresh foods, which leads to rapid oxidation, enzymatic reaction, and degradation of enzymes due to thermal processing [37]. However, there is significant information that shows food processing might not even necessarily have such a negative influence on the effectiveness of dietary ingredients [33].

6.1 Thermal treatments

The majority of commercially available food processing techniques include one or even more than one thermal process in order to achieve a variety of final products. The chemical content and nutritive values of the food material could change after the thermal process in addition to the desired consequence because of quantitatively or qualitatively changes in the amount of antioxidant properties, among several other factors. One of the main antioxidants, carotenoids, are widely distributed in tomatoes, watermelons, guava, papaya, and apricots [24]. Carotenoids are degraded if these food products are exposed to various treatments. Many vegetables and fruits contain phenols and phenolic substances. The majority of these food processing technologies include thermal treatments, which are reported that the plants do not have the ability to retain phenolic acids [38]. The outcomes of phenolic acids in food production can be significantly influenced by the product’s composition and the processing methods, but the dietary substrate has also been shown to be an even more important factor [7].

6.2 Nonthermal treatments

Cutting, blending, peeling, and crushing, as well as other nonthermal food processing technologies, could all have an influence on the antioxidant characteristics of food products. Additional “emerging” or “progressive” nonthermal food processing techniques have recently been developed, including high pressure, pulsed electric field, and ultrasonic processing [20]. Excessive temperatures could lead to their breakdown or polymerization, and that has negative consequences on some of these bioactive constituents, but they might also assist to extract higher carotenoids from the plant source. Various nonthermal processing technologies were suggested as alternative approaches to yield a product of a higher quality.

7. Changes in antioxidant bioavailability during food processing

Antioxidant compounds must be released from the food material through metabolism in the gastrointestinal tract and thereafter biologically modified into ingestible components in order to demonstrate their nutrition properties or to be active compounds [16]. In order to be used in metabolic processes, substances can then gradually enter the circulatory system and be delivered to the blood circulation, becoming “bioavailable” [39]. “Bioavailability” is a word that describes the transportation and diffusion of active ingredients to specific cells and tissues, enabling those cells and tissues to demonstrate a range of antioxidant actions [40]. Oral bioavailability has frequently been assessed through in situ digestive assays. These methodologies mimic digestion in the small intestine and gastrointestinal tract, and in certain cases, Caco-2 cell absorption simulation was achieved initially [41]. The concentration of these molecules, their intermolecular interactions, and the molecular structure of the plant and food products are the characteristics that have a substantial impact on the oral bioavailability and digestibility of natural antioxidant substances. The concentrations of various bioactive constituents in the respective food are influenced by pre and postharvest handling, resulting in a significant impact on plant-based product are composed. As an outcome, processed food products may have varying levels of dietary and possibly bioavailable antioxidant compounds. Furthermore, modifying the molecular structure of the essential constituents during food processing seems to have the chance to have a significant favorable or detrimental effect on availability [40]. Research on the contribution of food processing technologies on the bioavailability of antioxidants is completely lacking overall.

8. Applications of antioxidants

Natural and synthetically derived antioxidants have found wide applications in the food processing sector as food additives in meat, fruits, vegetables, beverage, spices, fats, and oil industries to enhance the appearance, taste, and color, and help prolong the shelf life. The addition of dietary antioxidants to meat and derived products has been observed to be effective in lipid oxidation and metmyoglobin formation. These compounds include plant phenolics as natural antioxidants, for instance, vitamin C—ascorbic acid and vitamin E—α-tocopherol (E306), culinary herbs, and spices, such as oregano, rosemary, basil, thyme, sage, pepper, nutmeg, clove, cinnamon, and extracts from tea and grape seed. The potential applications of natural extracts with antioxidant activity in food are being thoroughly investigated for potential uses, including health paybacks, nutritional profile improvement, and shelf-life extension [1].

Ascorbic acid, E300 is added to cut fruits, beers, jams, dried potato, and other foods to prevent foods from going brown due to oxidation reactions that cause discoloration. It is also added to replace the vitamin C lost during processing.

Rosemary oleoresin has proven to be as successful as polyphosphate and a combination of BHT and BHT-citric acid in automatically deboned poultry meat and sausages made from automatically deboned poultry meat [16, 34] worked on ethanolic extracts of rosemary and demonstrated that it improved the stability of butter and that this effect was concentration-dependent. The research study also assessed the ability of rosemary extract to inhibit copper-catalyzed oxidation and proved that the extract could chelate metal ions.

Pepper nigrum extract isolated using supercritical carbon dioxide extractions was found to be efficient in preventing lipid oxidation in ground pork samples. The potent antioxidant activity of pepper has been credited to piperine and piperine isomers, such as chavicine, isopiperine, isochavicine, and some monoterpenes.

Farag et al. showed that the essential oils of Cuminum cyminum and Thymus vulgaris inhibited the oxidation in butter that was stored at room temperature. At a concentration of 200 ppm, these essential oils were more efficient than Butylated hydroxytoluene in inhibiting the oxidation of lipids.

It is a fact that all emulsified products tend to have a shorter shelf life when compared to edible oils, due to their lesser resistance to microbial spoilage. They are, therefore, stored under refrigerated conditions, so that autoxidation is low and the naturally present tocopherols are stabilized them. Some edible oils, such as sunflower oil, are less resistant due to high polyunsaturation, often requiring the addition of natural or synthetic antioxidants. When it comes to frying oils, the best way to add antioxidants is just before their operation. It has been observed that adding rice bran oil with inherent natural antioxidants enhanced the shelf life of nuts processed in oils, such as soybean or rapeseed [20].

The application of synthetic antioxidants has to be reduced further and replaced by safer alternatives, such as natural or nature-identical antioxidants. Prolongation of the shelf life of highly processed foods has to be accomplished by modifying existing recipes, introducing culinary herbs and spices, which contain a high concentration of inherent antioxidants, using high-oleic edible oils requiring lower added antioxidant levels, and by use of natural protein hydrolysates, which have good synergistic activity.

9. Conclusions

There is increasing evidence to prove that consuming a range of dietary antioxidants available in natural foods reduces the risk of major health issues due to their antioxidant capability through several mechanisms. Care must be taken to choose optimal processing methods to ensure the quality of antioxidants from fresh fruits and vegetables and their products in order to achieve the objectives. The mode of action of these antioxidants in the body needs more research. Due to safety concerns, regarding the use of synthetic antioxidants and natural antioxidants acquired from edible sources, their by-products and coproducts are in the spotlight today. Further studies on the isolation of antioxidant compounds using nondestructive methods and their effects in animal models and human subjects are necessary to evaluate their potential benefits. Additionally, it is mandatory to confirm the bioavailability and lack of toxicity of such compounds. Delivery of isolated antioxidant metabolites as functional food ingredients or dietary supplements will help in promoting good health and reducing the risk of disease. In the last few decades, there has been considerable interest in the food as well as the pharmaceutical industry, for extracting and purifying antioxidants from natural sources. A sensible selection of appropriate food-handling methods right from the farm to the consumer for every type of product will make sure that the health-related benefits of specific antioxidants are maximized.