**3.2 Plants as source of phenolic acid**

The hydroxycinnamic acids are more common than are the hydroxybenzoic acids and consist chiefly of *p*-coumaric, caffeic, and ferulic. Indeed, caffeic acid, both free and esterified, is generally the most abundant phenolic acid and represents between 75 and 100% of the total hydoxycinnamic acid content of most fruit. Concentrations generally decrease during ripening but increase as the fruit increases in size [37]. The hydroxybenzoic acid content of edible plants is generally very low, except for certain red fruits, black radis and onions, which can have concentrations of several tens of milligrams per kilogram fresh weight [37]. Tea is important source of gallic acid; tea leaves may contain up to 4.5 g/kg fresh wt [37]. It has been stated that the most important PA derivatives are in the rapeseed oil including 2.6 dimethoxy-4-vinylphenol (257 μg/100 g) and ferulic acid (5.6 μg/100 g), while vanillic acid (11.4 mg/100 g) is in pumpkin seed oil and ferulic

**Figure 3.** *Structure of the important naturally occurring phenolic acids.* acid (5.8 mg/100 g) is in corn oil. The total amount of PA was determined as 79 mg gallic acid/kg oil in soy oil, 124 mg gallic acid/kg oil in canola oil, 8397 mg gallic acid/100 g oil in palm fruit, and 20–43 mg synapic acid/100 g oil in rapeseed oil [38]. PA content and profile in plant oil generally depends on the variety, environmental conditions, extraction methods, and storage conditions [39].

## **3.3 Health benefits**

Phenolic compounds are famous group of secondary metabolites with wide pharmacological activities. Phenolic acid compounds and functions have been the subject of a great number of agricultural, biological, chemical, and medical studies. Phenolic compounds in many plants are polymerized into larger molecules such as the proanthocyidins (PA; condensed tannins) and lignins. Moreover, phenolic acids may arise in food plants as glycosides or esters with other natural compounds such as sterols, alcohols, glucosides, and hydroxy fatty acids. Increases bile secretion, reduces blood cholesterol and lipid levels and antimicrobial activity against some strains of bacteria such as *Staphylococcus aureus* are some of biological activities of phenolic acids [40]. Varied biological activities of phenolic acids were reported. Phenolics acid possesses diverse biological activities, for instance, antiulcer, antiinflammatory, antioxidant, cytotoxic and antitumor, antispasmodic, and antidepressant activities [41]. Moreover, a phenolic compound can interrupt the radical chain reaction by donating a hydrogen stom to the free radicals and therefore converting itself to a radical. PA can also act as metal chelators and oxygen scavenger and helps then against diseases associated with oxidative stress [42].

#### **4. Tocols**

#### **4.1 Structure**

Tocopherols and tocotrienols, together abbreviated as tocols, are natural lipophilic antioxidants that protect oxidation in vegetable oils [43]. Tocopherols

**Figure 4.** *Structure of the important naturally occurring tocopherols.*

*Oilseeds as Functional Foods: Content and Composition of Many Phytochemicals… DOI: http://dx.doi.org/10.5772/intechopen.97794*

(vitamin E) are the most important and effective lipid-soluble compounds constituting a family of antioxidants with several health benefits [44]. Vit E comprise a chromanol ring with a C16 phytol side chain and are reclassified in two types according to which the side chain is either saturated (tocopherols) or contains three double bonds at carbons 3, 7 and 11 (tocotrienols). The presence of methyl (-CH3) group in the aromatic ring of tocopherol (**Figure 4**) makes this compound stable to heat, alkali, or acid. However, this vitamin undergoes degradation and isomerization under certain stress conditions, such as oxidizing agents or UV light, yielding four major vitamers: isomers (i.e., α-, β-, γ-, and δ-tocopherols) (**Figure 4**) and differ in the matylation patter of the benzopyran ring with three methyl groups (at C-5, C-7, and C-8) [45].

Among these homologs, α-tocopherol exhibits 100%biological activities, 30, 15, and 5% for β-, γ-, and δ-tocopherols, respectively. Seeds often dominate other plant parts in terms of the abundance of total-tocopherols (T-tocopherol), although α-tocopherol, a form of vitamin E that is most biologically active, is often only a minor component [44].

#### **4.2 Plants as source of tocopherols**

For tocopherols, the richest dietary sources are vegetable oils and the products made from these oils. Genetic factors and cultivars differences predominantly drive the expression of tocopherol compounds in seed oil exist. Vegetable oils contain not only α-tocopherol but also other tocopherols, especially γ and ∆ tocopherol [46]. The soybean and corn oils are usually dominated by γ-tocopherol while in olive oil the more abundant form is α-tocopherol [47]. The tocopherol contents in seed oils range from 2 to 8 mg/100 g of coconut oil to 113 to 183 mg/100 g of corn oil [48]. The amounts of tocopherols in vegetable oils vary according to variety, extraction method, and refining [49].

#### **4.3 Health benefits**

Plant lipids containing high level unsaturated fatty acids are prone to oxidation, therefore lipophilic antioxidants such as tocopherols are often found to co-exist with plant lipids, protecting the integrity and vitality of the plant [50]. Tocopherols and tocotrienols are vitamin E homologs, serving as strong antioxidants and having many essential physiological functions such as anticoagulant, essential regulator of metabolic processes including inflammation and cancer in humans [51]. Vit E is also indispensable for immune defense. It has been suggested that tocopherols, acting as hormones or as secondary donors of genetic information, control the expression of some genes [48]. Vit E deficiency causes the damage of cellular membranes resulting from oxidation of the unsaturated fatty acids in lipids, and vitamin E deficiency can also display itself as muscular pain and progressing muscular disorder [48].

Meanwhile, the importance of tocotrienols in human health both as vitamin E and bioactive components has received renewed recognition in recent years. Tocotrienols have hypocholesterolemic, anti-cancer and neuroprotective properties.

## **5. Carotenoids**

#### **5.1 Structure**

Carotenoids are natural pigments with yellow, orange, and red colors. More than 600 carotenoids have been identified in nature. Their physiological functions in promoting health are as pro-vitamin A and as antioxidants quenching singlet oxygen radicals (**Figure 5**). Carotenoids generally have a 40-carbon skeleton of isoprene unites cyclized at one or both ends [11]. The majority of carotenoids that occur in nature are in trans-form. Because of the long series of conjugated double bonds in the central part of its chemical structure, carotenoids exhibit light absorbing and unique singlet oxygen quenching capability [52]. Carotenoids can be classified as carotenes and xanthophylls, based on their chemical structure. α-carotene, β-carotene and lycopene are the predominant non-polar functional carotenoids and lutein is the primary polar functional carotenoids [53] (see **Figure 5**). Carotenes contain only a parent hydrocarbon chain without any functional group, while those bearing oxygen-containing functional group are called xanthophylls (e.g. astaxanthin, lutein, zaeaxanthin). Carotenoids can even be classified as provitamin A (e.g. α-carotene, β-carotene, and β-crytoxanthin) and non-provitamin A compounds [53]. Actually, carotenoids present various substitutions: terminal ring systems joined by the chromophore-bearing chain of conjugated double bonds (e.g. β-carotene), hydroxyls at the terminal rings (e.g. zeaxanthin, lutein), ketonegroups with or without additional hydroxy groups (e.g. astaxanthin and canthaxanthin), aromatic rings (e.g. synechoxanthin), and the rare monocyclic carotenoids (e.g. torulene). There are over 700 carotenoids, from which 40 are ingested in human diet from fruits and vegetables.
