*3.2.6 Ulvans*

Ulvans are mainly high sulfated polysaccharide existing in green algae (Ulva and Enteromorpha) and animal (glycosaminoglycans), belongs to heteropolysaccharides group, and water-soluble. Ulvans contain the basic units such as xylose, rhamnose 3-sulfate, iduronic acid, xylose 2-sulfate, and glucuronic acid and account for about 38 to 54% of dry algae mass. The units of α-L-rhamnose-3-sulfate-1,4-β-D-glucuronic acid, α-L-rhamnose-3-sulfate-1,4-α-D-iduronic, and α-L-Rhamnose-3-sulfate-1,4-β-D-xylose are repetition in the structure of ulvans [41]. Ulvans and their-derived oligosaccharides exhibit antioxidant activity via the level decrease of the total and LDL cholesterol and triglyceride reduction in the serum. The molecular weight of ulvans is a positive proportion to their antioxidant capacity. For example, hydroxyl radical scavenging ability and the molecular weight of ulvans ranged from approximately 50 to 90% and 18.2 to 100.5 kDa, respectively. Sulfate group number in ulvans also affect their antioxidant activity. For example, 2.0 mg/ mL of ulvan (32.8% w/w sulfate) of *U. pertusa* species arrested 90% hydroxyl radical that higher than native ulvan possessing 19.5% w/w sulfate [42]. Therefore, the over-sulfation of ulvans will have more benefits for antioxidant activity.

### *3.2.7 Pectins*

Pectins exist mainly in cell walls of terrestrial and marine plants, classified into a heterogeneous polysaccharide group. Pectins contain over 65% of 1,4-linked-α-Dgalacturonic acid that depends on species, for example, the galacturonic acid content of pectin in mangosteen rind (73.16%), in lime (72.5%), and mango peels (56.67%) [43]. Pectins are diverse on the structure and is usually classified based on esterified galacturonic acid units (methoxylation degree) as well as possesses different biological activities (antioxidant, antitumor, and anti-inflammatory). The main pectins in a plant are homogalacturonan, and unpopular (xylogalacturonan, rhamnogalacturonan I, rhamnogalacturonan II, arabinogalactan I, and arabinogalactan II. The structure, the content, molecular weight, and the plant species lead to a difference in the reaction rate constant between pectins and hydroxyl radical scavenging. Pectins in fresh white cabbage, carrot, onion, and sweet pepper exhibit antioxidant activity lower than Opuntia ficus indica. The rating constant for the reaction range from 2.05 ± 0.56 × 109 M−1 s−1 to (1.03–1.37) × 109 M−1 s−1. The rate constant also depends on the compositions in pectin compounds such as protein or secondary metabolites. Xanthine oxidase inhibition of pectin is improved when the molecular weight and a Gal residues number in pectin structure are high. Pectin of onion control inhibition of xanthine oxidase better than radical scavenging of DPPH and the hydroxyl [44]. Low etherified pectin helps the stabilization of malonic dialdehyde level and the inhibition of glutathione reductase and glutathione peroxidase [45]. Pectins have the content (2–35%) and the molecular weight (25–360 kDa) depending on plant species. Pectin after purifying is also white color, same purified alginate (**Figure 2b**).

#### **3.3 Secondary metabolites**

#### *3.3.1 Polyphenols (phlorotannins, lignins, polyphenols)*

Polyphenols are diverse in structure and exist in all different plants as well as marine (sponges). Polyphenol is named phlorotannin in marine. For terrestrial plants, polyphenols are determined, such as quercetin, tannin, gallic acid, mangrin, resveratrol, and lignin. Functional-antioxidant food is commercial in the market, for example, tannins, quercetin, gallic acid, mangrin, phlorotannins, or resveratrol, but not lignins. Lignins are antioxidant polyphenols existing in all plants interesting in the near time, especially their application into functional food and pharmaceuticals. Therefore, phlorotannins, lignins, and polyphenols are focused on the current chapter (**Figure 3**).

Phlorotannins that compose of the phloroglucinol units and the various linkages (ether, phenyl, ether/phenyl, and dibenzodioxin) are polyphenols in all marine plants and some marine animals [46]. Therefore, the structure of phlorotannins is diverse, and the thing leads to other bioactive of them, for example, antioxidant

#### **Figure 3.**

*(a) Crude fucoidan from brown algae Sargassum duplicatum grown in Vietnam; (b) chlorophyll powder from maize leaves; (c) glucosamine from shrimp shell.*

#### *Functional-Antioxidant Food DOI: http://dx.doi.org/10.5772/intechopen.96619*

[31, 47, 48], antitumor, anticancer, and inhibition of UV radiation [49]. Phlorotannins have two styles of free (existing in membrane-bound vesicles) and cell wall linkage (phlorotannins-alginic acid). Their content in brown algae is more than different marine organisms [50]. Phlorotannins content could reach up to 2% in brown algae growth in temperate regions of Pacific and Atlantic and tropical Atlantic regions [51]. Some studies noticed that phlorotannins in thallus dry weight are up to 25–30% [52]. For brown algae grown in Vietnam, antioxidant phlorotannin content is from 0.1–1.1%, compared to dried algae.

Lignins exist in the matrix of hemicellulose, cellulose, and lignin in the cell wall. Lignins are classified into an irregular polyphenol with monolignols (cinnamyl alcohols (guaiacyl), coniferyl alcohol (syringyl), sinapyl alcohol (p-hydroxyphenyl), and p-coumaryl alcohol) that cross-linked together via the linkages of carbon–carbon, ester, and ether. The ratio of monolignols in lignin structure is different between various plants [53]. Dehydrogenative polymerization of phenyl propanoid units helps to the synthesis of irregular lignin more advantageous. In-plant, lignins are formed via the metabolic pathway of phenylalanine/tyrosine. They account for up 10 to 25% of the dry plant mass and 1 to 43% in lignocellulosic biomass (cellulose, hemicellulose, and lignin). In the sugarcane and corn (stalk, stover, and straw), lignins are up to 25–32% and (6.9, 19.54, and 7.5), respectively [54]. Lignins are known for the free radical scavenging activity (2,2-diphenyl-1-picrylhydrazyl, DPPH• and (2,2′-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid, ABTS). The antioxidant efficiency of lignins depends on the structure and the solubility of lignins. Antioxidant activity is affected by the carbonyl groups of side chains but free hydroxyl groups and ortho-methoxy substitution in phenol ring impact. The molecular weight, the polydispersity, and the heterogeneity of lignins play a role in controlling their free radical scavenging capacity [55].

Polyphenols are known with one or more hydroxyl groups on the aromatic skeleton ring and possess antioxidant activity (scavenge free radicals, and inactivate prooxidants) [56], heart disease prevention, inflammation-reducing, anti-cancers, and antidiabetic, as well as the rate reduction of mutagenesis in human cells. Polyphenols are different in the structure, content, and antioxidant activity in various plants [57]. Nowadays, based on chemistry characteristics such as chemical structure, simple molecules, and highly polymerized compounds, scientists classify about ten different classes with over 8000 polyphenol structures. The relationship between antioxidant activities and the chemical properties of polyphenol is also noticed and demonstrated very clearly. Polyphenols presented in the current section are free polyphenols and belong to the group that dissolves in an organic solvent and aqueous, not alkaline and acid [58]. Common polyphenols in terrestrial plants are known, such as quercetin, rutin, tannin, gallic acid, catechin, resveratrol, mangiferin, and epicatechin.

#### *3.3.2 Alkaloids*

Alkaloids are one of phytochemistry composition in plants, composed of at least one nitrogen atom with hydrogen-carbon groups in an amine-type structure, and accumulate nearly 20% of plant species. They are mainly well-known as pyrrolizidines, pyrrolidines, pyridines, isoquinolines, tropanes, indoles, quinolines, morphine, strychnine, quinine, ephedrine, and nicotine [59]. Alkaloids possess antioxidant activity, such as radical scavenging potential, total antioxidant activity, ferric reducing antioxidant potential, hydroxyl group scavenging ability, and lipid peroxidation inhibition ability. Alkaloids play a controlling role in antioxidant activity better than phenols [60, 61]. Alkaloids content and their activity are a correlation to the species and growth time of plants. For example, alkaloids are the major antioxidants in maca. Hydroxylated alkaloids exhibit antioxidant activity based on the reaction between radicals with high lipophilicity. However, the solvation process causes a decrease in the antioxidant activity of alkaloids [62].
