Some important fruits having antioxidant constituents.
Antioxidants are the defense system of the body against the damage of reactive oxygen species, which is normally produced during the various physiological processes in the body. There are various sources of these antioxidants like endogenous antioxidant present in the body and exogenous food source. In recent decades, alternate of synthetic food antioxidants by natural ones has fostered interest on vegetable sources and the screening of inexpensive raw materials particularly from the agriculture for identifying new antioxidants. Polyphenols are the significant plant compounds with antioxidant activity, though not the only ones. Some but not only restricted to biological properties such as anticarcinogenicity, antimutagenicity, antiallergenicity, and antiaging activity have been reported for natural and synthetic antioxidants. Among the sources of natural antioxidants, the most important are those coming from routinely consuming vegetables and fruits; however, antioxidant from other plant and agriculture waste should not be ignored.
The formations of oxygen reactive forms as a result of rigorous oxidative processes taking place in human organism are the potent precursors of systemic cells and tissues damage. Antioxidants being an inhibitor of the oxidation process remove these free-radical intermediates by oxidized themselves , even at quite diminutive concentration, and thus have assorted physiological function in the body to stop these oxidation reactions ultimately protecting the body from harmful chain reactions . Thus, they have reviewed by many researchers as nature’s answer to physiological and environmental stress, atherosclerosis, aging, and cancer . Body’s endogenous defense system against these free radicals plays an imperative role, which can further supported by the supplementation of antioxidants in the diet. Generally, antioxidants can be divided into two major categories such as synthetic and natural. The main targeted site of these free radicals damage and defensive approach of antioxidants in the body is at the cellular level. Based up on this, these antioxidants can also be classified as enzymatic and nonenzymatic antioxidants. Enzymatic antioxidants primarily include glutathione peroxidase, catalase, and superoxide dismutase. There are also several other enzymes in the body that contribute to the total antioxidant capacity, which reflects in the serum . Nonenzymatic antioxidants contain several subdivisions mainly vitamins such as A, E, C, and to lesser extent vitamin D, enzyme cofactors (Q10), peptides and some minerals (zinc and selenium). The major ingredients from the natural sources are polyphenolic compounds, which are reported to have significant antioxidant potential . A detailed classification and subclassification has been displayed in Figure 1.
Natural antioxidants are primarily phenolics that may occur in all parts of plants , such as fruits, vegetables, nuts, seeds, leaves, roots, and barks. In the recent past, some toxicological studies regarding the use of synthetic antioxidants have shown their unwanted or adverse effects. These reports have urged the researchers to focus their study on exploring the natural sources with reasonable antioxidant potential . Moreover, the availability and economy are significant concerns too in the context of using these natural antioxidants. The antioxidants from the nature can be categorized into the various subclassifications. However, two major categories are like antioxidants from commonly consumed or routine natural diets (e.g., vegetables, fruits, cereals, and beans) and secondly from plant or herb source that have fair antioxidant potential but are not the routine dietary source (e.g., medicinal plants and wild herbs). Among these, the routine dietary sources are very important as these can be easily available and more suitable for the dietary interventions. The need is to identify and generate awareness about these sources, which can be rated from top to down regarding antioxidant potential. The people who are habitual of consuming these vegetables and fruits in their routine meal are reported to be less affected by various chronic diseases , and studies have also endorsed the long-term healthy impact of consuming these nature-origin diets. Most common dietary supplements are comprised of vitamins C and E from synthetic as well as natural sources. Vitamin C is rich in the citrus fruits, which is a renowned fact, so fruits such as orange, lemon, blueberries, strawberries, grapes, prunes, and plums; red beans; spinach; kale; broccoli flowers; and alfalfa sprouts have good amount of antioxidants . Fortunately, these are the part of our routine diet; however, their availability pertaining to the geographical distribution as well as cultivation is an important factor. Though international trading made them available throughout the world and even in the off season as well, the consumption of seasonal and fresh fruits is always encouraged. Vitamin E is a fat-soluble vitamin and exerts its antioxidant effect by reducing fat oxidation in the body . Synthetic form of this vitamin is comprised of α-tocopherol, which is widely used as food supplement. The natural form of this vitamin contains mixed tocopherols almost having eight isomeric forms of α-tocopherol. The availability of these mixed tocopherols enhances the percent absorption of vitamin E from the natural sources in the human body.
An enormous growth has been observed in the vitamin supplement market during the past decade. It is estimated worth $68 billion with the US renders to be major shareholder, i.e., around 30%. A $421 million for just vitamin E and $361 million for vitamin C business has been recorded from Europe. Moreover, according to a report from Business insight, an annual growth of 4.5% in US vitamin and mineral market, i.e., almost $30 billion in the first half of this decade, was forecasted .
The targeted approach of the researchers around the world to date is to find natural sources of antioxidants, which will be inexpensive and closer to the nature. These findings will be the superior substitute of synthetic supplements in food, pharmaceutical, and cosmetic industries . Though significant harmful effects of synthetic supplements have not been reported to date, a common concept of closer to nature is obviously a better approach in the supplementation. The coming decade will be the era of natural products, and exploration of natural antioxidants will be the prime focus of the researchers .
The main objective of the current chapter is to overview and summarize the natural sources with antioxidant potential. The summarized data will be a useful information for the professional and nonprofessional readers to gather a fair information regarding dietary and non-dietary sources in the nature, which can be the part of the routine diet to enhance the antioxidant capability of the body.
2. Natural antioxidants
The nature is always a significant and rich source of countless ingredients that can be served as health-promoting agents. Many of these natural sources include routinely used fruits, vegetables, herbs, spices, and edible mushrooms that can be the part of routine diet. In addition to that, there is a huge list of medicinal plants reported to have extensive health-boosting potentials. One of the most beneficial effects from these natural sources is due to their potential antioxidant properties. Regarding the antioxidant capability, the researchers have focused their studies to explore the most potential sources along with their active ingredients. The researchers have added some marine sources such as algae and seagrass as well in the list of these natural sources. The recent studies have also explored the role of naturally occurring microbiome in the gut in the body antioxidant pool denoted as good bugs. These good bugs can also be used as supplement called as probiotics. Thus, generated literature is a big data bank for the researchers of the field and beneficial information for the general reader as well. There is a need to summarize this enormous data bank based upon the identification of most potential sources, which will make the literature feasible for the professional and nonprofessional readers at the same time. This chapter will elaborate the various natural sources of antioxidants that hopefully help to prioritize the beneficial amendments in dietary composition.
Fruits and vegetables are highly recommended dietary contents, widely known for their health-promoting effects and nutritious values. They got an essential place as conventional foods in the history because of their excessive amount of minerals, specifically electrolytes; vitamins, specifically vitamins C and E; while various current studies are revealing their phytochemical contents, having antioxidant capabilities . These antioxidants scavenge the oxidants or free radicals produced as a result of several degenerative and disease processes such as diabetes, cancers, and cardiovascular disorders. So, regular consumption of fruits and vegetables may reduce the risk of mortality associated with these diseases . Most of the natural antioxidants convert the lipid radicals into more stable products by breaking the chain. Antioxidants obtained from vegetables and fruits are mostly of phenolic structure, which may include vitamins, minerals, and polyphenols . Antioxidant minerals, such as iron, zinc, selenium, copper, and manganese, act as cofactor of many antioxidant enzymes, absence of which may certainly disturb the activity of their enzymatic scavenging activity . The antioxidant capability of different fruits is being presented in Table 1.
2.1. Types of antioxidants from fruits and vegetables
Polyphenols, present in fruits and vegetables, is a group of several low- and high-molecular-weight compounds having antioxidant properties that prevent lipid oxidation . Most of them are conjugates of mono and polysaccharides connected with one or more groups of phenol rings or may also present as functional derivatives such as esters and methyl esters . This major class of natural antioxidants can be obtained from teas, particularly green and red teas, as well as fruits such as grapes . However, polyphenols from teas have more significant than in fruits because of their bioavailability in blood. Approximately 15–20% polyphenols are absorbed in human blood from their consumed amount. This absorption is enhanced when there are no sugar molecules attached with them. So, teas have more absorption of polyphenols than in fruits because of high sugar content in fruits .
Flavonoids, another important antioxidant content, is a subclass of polyphenols present abundantly in most of the foods, such as potatoes, wheat, tomatoes, red berries, peaches, and almonds . Anthocyanin is a subcategory of flavonoids (Figure 1) which is present in berries and red wine. It is a potent antioxidant with decreased bioavailability as compared to other flavonoids . Polyphenols show their antioxidant properties by preventing the oxidation of low-density lipoproteins (LDL), thus preventing plaque formation . Some types of polyphenols have also been found to inhibit the oxidation of some important enzymes and thus preserve their proper functioning . Carotenoids are another major class of phytochemicals antioxidants from fruits and vegetables after polyphenols. They mostly found in vegetables, such as potatoes, carrots, papayas, and apricots .
Among the vitamins obtained from fruits and vegetables, acting as antioxidants, vitamin C, also known as ascorbic acid, is a very potent water-soluble antioxidant commonly found in citrus fruits and vegetables such as oranges, lemons , and tomatoes . It is recommended that the fruits and vegetables containing vitamin C should be taken in small divided doses instead of having a large dose simultaneously because vitamin C shows less absorption when given in large quantities .
Another vitamin with antioxidant properties is vitamin E, which is related to tocopherol family of antioxidant. It is a fat-soluble, nonpolar vitamin found naturally in lipid-rich fruits and vegetables, such as olives, sunflower, and nuts . Vitamin E shows higher bioavailability than vitamin C, which is perhaps due to its fat solubility and can be further enhanced when taken with fatty foods .
2.2. Antioxidants from fruits and vegetables wastes
Fruits and vegetable waste material is produced during their cultivation, industrial management, processing, preservation, and distribution . In the past few decades, researchers have been struggling to device the methods to recycle these wastes to get therapeutic benefits . The vegetables and fruit waste material includes peelings, trimming, shells, seeds, stems, and pulp residues that remained after extraction of juices and starch or sugar preparation. This waste constitutes about 25–30% . According to a research, greater amounts of phenols and ascorbic acids have been reported in these waste scalps than their pulp  and in unripe form than their ripened form . Most of the fruit peels contain 2–27 times greater amount of antioxidants than their pulp . According to Someya et al., banana pulp possesses 232 mg/100 g of phenolic components, and this amount is just 25% of the amount present in banana peels .
A lot of antioxidants, such as carotenoids, phenolic compounds, vitamin C, and dietary fibers, are found in mango peel. These compounds have reported activity against many degenerative diseases, such as Alzheimer’s disease, cataracts, cancer, and Parkinson’s disease . The wastes of wine-making industry include degradable solids such as skin, stem, and seeds, which contain many antioxidants that have shown to prevent many degenerative processes and possess health-promoting effects . Pujol et al.  reported that the coffee wastes from the coffee industry contains approximately 6% polyphenols and about 4% tannins. Antioxidant ingredients from various sources of fruit waste have been presented in Table 2.
|No||English name||Antioxidant contents||Concentration (ORAC value)||References|
|2.||Guava||β-Carotene, lycopene, vitamin C, ellagic acid, anthocyanin|||
|3.||Pears||Ascorbic acid, flavonoids (quercetin, isorhamnetin, myricetin, kaempferol, and luteolin), betalains, taurine, total carotenoids and total phenolics||135 (mmol TE/g)|||
|4.||Pomegranate||Vitamin C and polyphenols||1245 (mmol TE/g)|||
|5.||Papaya||Quercetin and β-sitosterol||300 (mmol TE/g)|||
|6.||Water melon||Lycopene, β-carotene, vitamin C||100|||
|7.||Apple||Proanthocyanidins, flavonoids (kaempferol, quercetin, and naringenin derivatives); phenolic acids (protocatechuic, caffeoylquinic, and hydroxycinnamic acid derivatives); hydroxychalcones (phloretin and 3-hydroxyphloretin derivatives); and isoprenoid glycosides (vomifoliol derivatives)|
Flavanols, flavonols, dihydrochalcones, and hydroxycinnamates
|16.78 a ± 0.25|
1508 ± 44 (μmol/100 g)
|8.||Plum||Proanthocyanidins, flavonoids (kaempferol, quercetin, and naringenin derivatives); phenolic acids (protocatechuic, caffeoylquinic, and hydroxycinnamic acid derivatives); hydroxychalcones (phloretin and 3-hydroxyphloretin derivatives); and isoprenoid glycosides (vomifoliol derivatives)||14.55 c ± 0.21|
94.8 (mmol TE/g)
|9.||Guava||β-Carotene, lycopene, vitamin C, ellagic acid, anthocyanin|
|10.||Beet root||Betalains, vitamins C and E, carotenoids, flavonoids, and thiol (SH) compounds||4100 (dry extract)|
115 (μmol TE/g)
|11.||Pea||Vitamins C and E, carotenoids, flavonoids, and thiol (SH) compounds||19 (μmol TE/g)|||
|12.||Carrot||Vitamins C and E, carotenoids, flavonoids, and thiol (SH) compounds||60 (μmol TE/g)|||
|13.||White cabbage||Vitamins C and E, carotenoids, flavonoids, and thiol (SH) compounds||61 (μmol TE/g)|||
|14.||Tomato||Vitamins C and E, carotenoids, flavonoids, and thiol (SH) compounds||67 (μmol TE/g)|||
|15.||White onion||Vitamins C and E, carotenoids, flavonoids, and thiol (SH) compounds||85 (μmol TE/g)|||
|16.||Cauliflower||Vitamins C and E, carotenoids, flavonoids, and thiol (SH) compounds||102 (μmol TE/g)|||
|17.||Spinach||Vitamins C and E, carotenoids, flavonoids, and thiol (SH) compounds||152 (μmol TE/g)|||
|1.||Banana||Unripe (green) fruit and peel||Phenols and flavonoids||[156, 157]|
|2.||Mango||Peel, kernel||Gallic acid, ellagic acid, gallates, gallotannins, condensed tannins||[158, 159]|
|3.||Water melon||Peel, rinds||Citrulline, lycopene, flavonoids, and phenols||[160, 161]|
|4.||Cucumber||Peel||Flavonoids and phenols|||
|5.||Potato||Peel||Chlorogenic acid, caffeic acid, ferulic acid, and phenols||[162, 163]|
|6.||Coffee||Coffee ground and residue||Polyphenols, tannins, and gallic acids||[164, 38]|
|7.||Apple||Peel||Epicatechin, catechins, anthocyanins, quercetin glycosides, chlorogenic acid, hydroxycinnamates, phloretin glycosides, and procyanidins|||
|8.||Grapes||Skin and seeds||Coumaric acid, caffeic acid, ferulic acid, chlorogenic acid, cinnamic acid, neochlorogenic acid, p-hydroxybenzoic acid, protocatechuic acid, vanillic acid, gallic acid, proanthocyanidins, quercetin 3-o-gluuronide, quercetin, and resveratrol||[166, 167]|
|9.||Guava||Skin and seeds||Catechin, cyanidin 3-glucoside, galangin, gallic acid, homogentisic acid, and kaempferol|||
|10.||Pomegranate||Peel and pericarp||Gallic acid, cyanidin-3,5-diglucoside, cyanidin-3-diglucoside, and delphinidin-3,5-diglucoside||[169, 170]|
|12.||Cucumber||Peel||Phenols, flavonoids, pheophytin, phellandrene, caryophyllene||[33, 160]|
|13.||Potato||Peel||Gallic acid, caffeic acid, vanillic acid, chlorogenic acid, ferulic acid, and phenols||[160, 162, 163]|
|14.||Tomato||Skin and pomace||Carotenoids|||
2.3. Mushrooms as antioxidant
In the nutrition world, mushrooms are delegated vegetables; however, they are not actually plants. They have a place with the kingdom of fungi. In spite of the fact that they are not vegetables, mushrooms give imperative supplements. Mushrooms are considered as healthfully utilitarian sustenance and also source of valuable medicines [39, 40]. Numerous consumable mushrooms (for the most part Basidiomycetes) are great wellsprings of important nutritive components including carbohydrates, for example, β-glucans; lipids; B-vitamins, such as niacin, flavin, and pyridoxine; phenolics, like tocopherols; organic acids, for example, malate ascorbate, fumarate, and shikimate; monoterpenoid and diterpenoid; proteins, for example, hydrophobins; and trace components, for example, selenium [41, 42, 43]. These components are established as to be responsible for immunomodulatory, antimicrobial, antitumor, antihypertensive, hepatoprotective, and antioxidant activities of mushrooms [44, 45].
The amount of mushrooms on Earth is assessed at 140,000 yet might be just 10% (approximately 15,000 species) are known [43, 46]. Out of approximately 15,000 known species, 2,000 are found safe for human utilization, and around 650 of these contain therapeutic properties . There are a number of mushrooms including
2.4. Medicinal plants and spices having antioxidants
2.5. Antioxidants from marine sources
Marine ecosystem has been reported as a potential source of biodiversity and chemical activities. The organisms living in marine environment are gaining the attention of industries such as pharmaceuticals, nutraceuticals, and cosmetics because of possessing various interesting and useful chemical compounds . Marine biotechnologists are trying to produce the tool for the utilization of marine biodiversity for the production of cheap source of pharmaceutical products and functional foods . Seaweeds and sponges are considered as the richest source of bioactive compounds having the antimicrobial and antioxidant activities . Seaweeds and sponges with their associated bacteria have been found to possess various health-promoting and disease prevention effects due to their phenolic compounds, polysaccharides, and useful organic acids . These are supposed to be the most protective group of foods against environmental pollutants and radiation . Among various other useful compounds, the marine organisms also contain polyphenolic compounds that are responsible for antioxidant activity including flavonoids, benzoic acid, cinnamic acid, gallic acid, quercy, and phlorotannins . Nonanimal sulfated polysaccharides are reported to have antioxidant activities , which can be obtained from marine algae and other marine organisms from the phaeophyta group .
A large number of different species of algae and microalgae have been studied for the use of their bioactive contents as functional food components. Algae comprised of a huge and complex group of photosynthetic organisms with simple reproductive organs, which can be multicellular, known as macroalgae and unicellular called as microalgae. Algae grow in extremes of environmental conditions such as light, temperature, and salinity, which results in the production of a large number of reactive oxygen species (ROS). To cope with these ROS, algae produce various secondary metabolites with many antioxidant activities such as phycobilins, polyphenols, carotenoids, and vitamins .
People living in coastal areas use many types of seaweed, both as fresh and dry forms, as a natural source of food, and from the research, it is known that these seaweeds contain a large amount of proteins, minerals, and vitamins. Although the composition of these seaweeds varies according to their species, geographical distribution, temperature, and seasonal variation, the overall nutritional value remains the same. Many compounds from marine algae possess anticancer activity, and recently, seaweeds have gained attention as a rich source of antioxidants . Many of the secondary metabolites produced by marine organisms reflect the presence of chloride and bromide ions in seawater. Marine halogenated compounds assemble a large number of other useful compounds such as indoles, peptides, terpenes, phenols, acetogenins, and volatile halogenated hydrocarbons. This protective effect suggests the presence of antioxidant compounds that show their antioxidant activity as free radical scavengers, hydrogen-donating compounds, single oxygen quenchers, and metal ion chelators. Many biological compounds have previously isolated from some other marine organisms such as fish, crustaceans, and their byproducts .
Seaweeds also create a suitable environment to a large number of bacteria that live on their surface having much more diversity of microorganisms as compared to other multicellular organisms . These associated microorganisms have a protective effect on the seaweeds from pathogen, and they produce a large number of bioactive compounds of biomedical importance . Exopolysaccharides produced by these bacterial species are used as an ingredient in food, petroleum, and pharmaceutical industries and emulsification of crude oil, vegetables, mineral oils, and bioremediation agents in environment management systems .
Fish protein hydrolysate (FPH), which is prepared from various marine organisms such as mackerel, tuna, Alaska Pollock, and yellowfin sole, has also been reported to have antioxidant activity [139, 140, 141]. Many types of peptides are obtained from fish muscle, bone, skin, and other tissues. All of these amino acids can scavenge-free radicals, but the most powerful scavenging activity attributes to those who can easily donate hydrogen atoms. These amino acids are cystine and methionine, which have nucleophilic sulfur-containing side chains or tryptophan, tyrosine, and phenylalanine, which have aromatic side chains. Peptide size and amino acid composition are important for the FPH because it determines its antioxidant nature .
An in vitro study on phycocyanin, a pigment obtained from blue-green algae, reveals its antioxidant activity. It was evaluated in vitro by the use of luminol-enhanced chemiluminescence (LCL). Luminol reacts with oxygen (O−2), alkoxyl (RO˙), and hydroxyl (OH˙) radicals and shows a luminous signal measurable before and after antioxidant addition. This antioxidant activity was also confirmed in vivo by induction of inflammation in mice paw with glucose oxidase. The edema caused by inflammation was reduced, and the luminous signal indicated that the phycocyanin can scavenge OH˙ and RO˙ . Algal antioxidants are also used in the cosmeceutical industries as antiaging agents . A carotenoid pigment known as astaxanthin, found in microalga
An increasing interest has been observed from the past decade in exploring the natural ingredients to be used in the food and food products. The researchers from all over the world are focusing on the alternate sources other than the synthetic one, which will be more safe and convenient as dietary component. Although there are no such harmful reports have been observed regarding the use of synthetic antioxidants however the consumer’s interest is also compelling toward the nature close products. Moreover, the synthetic antioxidants and preservatives in the food may lead to lipid peroxidation and deterioration of food flavor and quality. The use of natural herbs, spices, and plant ingredients is in practice from the ancient times and still practiced in the traditional food preparation as preservative, aroma, and flavor. This chapter is an effort to overview the potentials of various natural sources having reasonable antioxidant potential. The literature reports compiled here will be beneficial to identify the significance of various natural sources based on their antioxidant capacity, active ingredients, and geographic availability. This chapter reveals that people can prioritize their dietary habits based on the antioxidant potential and cost-effectiveness of the available source because 70–80% of the world population cannot afford the modern supplement and medicines.