**4.1. Chemical structure**

**4. Anthocyanins**

**Flavonoid subclass**

Anthocyanins Cyanidin

Chalcones Cinnamon

Flavanols Catechin

Flavanones Hesperetin

Flavonols Quercetine

Flavones Apigenin

Isoflavones Genistein

Delphinidin

Epigallocatechin Epigallicatechingallate

Flavanonols Taxifolin or dihydroquercetin

Naringenin Eriodiclyol

Kaempferol Myricetin

Luteolin

Daidzein Glyatein

**Table 1.** Dietary sources of flavonoids [28, 91–98].

Methylhydroxychalcone

122 Phenolic Compounds - Natural Sources, Importance and Applications

Aromaderin or dihydrokaempherol

cies rich in anthocyanins [105–107].

they also occur in the flesh (cherries and strawberries).

Anthocyanins are the largest group of phenolic pigments and the most important group of water-soluble pigments in plants [68, 69, 101–104], responsible for the red, purple and blue colors found in many fruits, vegetables, cereal grains and flowers, being odorless and nearly flavorless and contributing to taste as a moderately astringent sensation. Anthocyanins are almost universally found in higher plants (occurring in about 30 families), but in general anthocyanins seem to be absent [103] in the liverworts, algae and other lower plants, although some of them have been identified in mosses and ferns. **Figure 2** shows a picture of plant spe-

Xanthones Mangostin Mango, mangosteen, bark of pear, apples, cherries

**Prominent food flavonoids Typical rich food sources**

Bilberries, black and red currants, blueberries, cherries, chokeberries, elderberries, grapes, strawberries, pomegranate

Apples, blueberries, grapes, onions, lettuces, red wine, tea, chocolate, apricots, sour cherries, grape juice, mint

Apples, bean, blueberries, buck wheat, cranberries, endive, leeks, broccoli, lettuces, onions, olive, pepper, tomatoes

Citrus fruits, celery, parsley, spinachs, rutin, olives, artichoke

Soybeans, grape seed/skin, chick peas, black beans, green peas

Apples, pears, strawberries, tomatoes, cinnamon

Grapes, red onion, açai palm

Citrus fruits and juices, peppermint

Anthocyanins are found mainly in the skin, except for certain types of red fruit [94], in which

Anthocyanin biosynthesis was one of the first branches of the general propanoid metabolism [41, 108, 109], for which biosynthetic enzymes and corresponding transcription factors were identified, given the ease of visualization and control of mutants and genetic imbalances.

Anthocyanins have characteristic physicochemical properties that confer them its unique color and stability [30, 32, 110–112]. They are highly reactive molecules and thus sensitive to Chemically, anthocyanins are glycosylated polyhydroxy or polymethoxy derivatives of 2-phenylbenzopyrilium [68, 103, 114], usually with molecular weights ranging from 400 to 1200 (medium-size biomolecules) and containing two benzyl rings (A and B). Anthocyanins usually contain a single glucoside unit, but many anthocyanins contain two, three, or more sugars attached at multiple positions [79], or occurring as oligosaccharide side chains. Intensity and type of the color of anthocyanins is affected by the number of hydroxyl and methoxyl groups [68, 115]: if more hydroxyl groups are present then the color goes toward a more bluish shade; and redness is increased if more methoxyl groups are present. The major anthocyanins are shown [116, 117] in **Figure 3** and **Table 2**.

Anthocyanins mainly exist in glycosidic forms in fruits and with the exception of blueberries, fruits usually contain anthocyanin derived from only one or two of the aglycone bases. Grapes offer a richer anthocyanin profile than many other fruits [118] (red grapes may contain a mixture of more than 20 pigments [85, 119]. Various berries and black currants are the anthocyanin-richest fruits [120–122]. The eggplant is only one common vegetable [123] that contains a high level of anthocyanins.

**Figure 3.** Structure of the major anthocyanins-3-O-glucoside present in fruits [29, 116, 117].


**Table 2.** Major anthocyanins-3-O-glucoside present in fruits [29].

The anthocyanins are all amphoteric [32, 34] forming salts with either acids or bases. In addition, anthocyanins occur in plants as salts (indicated by the positive charges on the heterocyclic ring) and their color in plant cells depends mainly upon their mode of combination. The conjugated bonds in their structures (light-conjugated double bonds carrying a positive charge), which absorb light at about 500 nm, are the basis of the bright red, blue and purple color of fruits and vegetables [124] as well as the autumn foliage of deciduous trees. Every color except green has been observed (either natural or synthetic), depending on aspects such as a kind of substituent present in the B-ring, the local pH, the state of aggregation of the anthocyanins, complexation by organic molecules, or, as in the case of blue color [125], complexation by metal cations.

In spite of the increasingly large number of structures, they are derived from only about 30 different anthocyanidins [69, 126], most of them are based on cyanidin (31%), delphinidin (22%), or pelargonidin (18%). The other common anthocyanidins (peonidin, malvidin and petunidin), which contain methoxy group(s) on their B-ring (**Figure 4**), represent together 21% of the isolated anthocyanins. One new methylated anthocyanidin, 7-O-methylcyanidin, five new desoxyanthocyanidins and a novel type of anthocyanidin called pyroanthocyanidin [11, 127] have also been reported. In spite of the structural diversity of anthocyanins, the three nonmethylated anthocyanidins are the most widespread in nature [128], which are present in 80% of pigmented leaves, 69% of fruits and 50% of flowers.

### **4.2. Antioxidant activity**

The relationship between diet and health has been known since ancient times and recent studies demonstrated the relevance of many food components in modulating health [1]. Due to anthocyanin's positive charge (**Figure 3**), the number and arrangement of aromatic hydroxyl groups, the extent of structural conjugation and the presence of electron-donating and electron-withdrawing substituents in the ring structure made anthocyanins very effective donors of hydrogen to highly reactive free radicals (such as superoxide (O<sup>2</sup> − ), singlet oxygen (1 O2 ), peroxide (RCOO⋅), hydrogen peroxide (H<sup>2</sup> O2 ) and hydroxyl radical (OH⋅) and reactive nitrogen species in a terminator reaction) and, thereby preventing further radical formation Anthocyanin Pigments: Importance, Sample Preparation and Extraction http://dx.doi.org/10.5772/66892 125

**Figure 4.** Structure of the main anthocyanins.

[55, 91, 129]. This effect protect cells from oxidative damage, which leads to aging and various diseases [102, 130–133], such as cancer, neurological and cardiovascular diseases, inflammation, diabetes and bacterial infections. The antioxidant capacity of phenolic compounds is also attributed to chelate metal ions involving in the production of free radicals [134], thereby reducing metal-induced peroxidation. Anthocyanin bioavailability has been the subject [135– 138] of recent reviews.

Laboratory-based evidence was provided (the potential health benefits of anthocyanins [139]. Consumption of diets rich in natural bioactive components (i.e., fruits and vegetables) as an alternative to pharmaceutical medication has been a subject [104, 140, 141] of considerable interest to researchers. In recent investigations carried out in population-based anthocyanins have been linked to a decrease in the incidence of several diseases, such as diabetes mellitus, cancer and cardiovascular diseases. *In vivo* studies have reported evidence regarding the positive association of their intake with healthy biological effects. However, much work remains to achieve definitive conclusions [139, 142] and the need for additional basic and applied research in this area is evident.

### **4.3. Color**

The anthocyanins are all amphoteric [32, 34] forming salts with either acids or bases. In addition, anthocyanins occur in plants as salts (indicated by the positive charges on the heterocyclic ring) and their color in plant cells depends mainly upon their mode of combination. The conjugated bonds in their structures (light-conjugated double bonds carrying a positive charge), which absorb light at about 500 nm, are the basis of the bright red, blue and purple color of fruits and vegetables [124] as well as the autumn foliage of deciduous trees. Every color except green has been observed (either natural or synthetic), depending on aspects such as a kind of substituent present in the B-ring, the local pH, the state of aggregation of the anthocyanins, complexation by organic molecules, or, as in the case of blue color [125], com-

**Anthocyanidin Abbrev. R1 R2 λmax (nm)\* Some of the produced colors R3**

Delphinidin Dp OH OH 546 541 Purple, mauve and blue

Cyanidin Cy OH H 535 530 Magenta and crimson

Petunidin Pt OH OCH3 543 540 Purple Malvidin Mv OCH3 OCH3 542 538 Purple

Peonidin Pn OCH3 H 532 528 Magenta Pelargonidin Pg H H 520 516 Orange salmon

**Table 2.** Major anthocyanins-3-O-glucoside present in fruits [29].

124 Phenolic Compounds - Natural Sources, Importance and Applications

 **= H R3**

 **= gluc**

In spite of the increasingly large number of structures, they are derived from only about 30 different anthocyanidins [69, 126], most of them are based on cyanidin (31%), delphinidin (22%), or pelargonidin (18%). The other common anthocyanidins (peonidin, malvidin and petunidin), which contain methoxy group(s) on their B-ring (**Figure 4**), represent together 21% of the isolated anthocyanins. One new methylated anthocyanidin, 7-O-methylcyanidin, five new desoxyanthocyanidins and a novel type of anthocyanidin called pyroanthocyanidin [11, 127] have also been reported. In spite of the structural diversity of anthocyanins, the three nonmethylated anthocyanidins are the most widespread in nature [128], which are present in

The relationship between diet and health has been known since ancient times and recent studies demonstrated the relevance of many food components in modulating health [1]. Due to anthocyanin's positive charge (**Figure 3**), the number and arrangement of aromatic hydroxyl groups, the extent of structural conjugation and the presence of electron-donating and electron-withdrawing substituents in the ring structure made anthocyanins very effective

O2

nitrogen species in a terminator reaction) and, thereby preventing further radical formation

−

) and hydroxyl radical (OH⋅) and reactive

), singlet oxygen

donors of hydrogen to highly reactive free radicals (such as superoxide (O<sup>2</sup>

plexation by metal cations.

Source: Ref. [29].

**4.2. Antioxidant activity**

(1 O2

80% of pigmented leaves, 69% of fruits and 50% of flowers.

), peroxide (RCOO⋅), hydrogen peroxide (H<sup>2</sup>

Anthocyanins are the pigment compounds responsible for pale yellow, orange, red, magenta, violet and blue colors [143]. Carotenoids and betalains confer yellow and red colors [144], although only the families of Caryophyllales (except for Caryophyllaceae and Molluginaceae) produce betalains. Up to now, no plants producing both anthocyanins and betalains [109] have been discovered. Anthocyanins, carotenoids and other pigments contribute to the UV patterns that are visible to insects and serve [145] to signal flowers that are attractive to pollinators. **Figure 5** shows a schematic representation of the biochemical process involving anthocyanins in color plants [146].

**Figure 5.** Schematic of the general flavonoid biosynthetic pathway relevant to flower color (ANS: anthocyanidin synthase; CHI: chalcone isomerase; CHS: chalcone synthase; DFR: dihydroflavonol 4-reductase; F3H: flavonoid-3′ hydroxylase; F3´5H: flavonoid-3′5´hydroxylase FLS: flavonole synthase; 3GT: flavonoid 3-O-glucosyltransferase; MT: Malonyl transferase) [146].

In food chemistry, anthocyanins have been studied [68, 147, 148] in relation to changes and stability of colors in foods such as fruits during processing and storage and also for their use as natural colorants. Indeed, many types of anthocyanin food colorants have been developed and are now available to customize the appearance of foods. In horticulture, color conversion of flower pigments has become possible by new findings of anthocyanin research. Creation of flowers in new colors enriches our life; for example, the creation of blue roses [109] is a noteworthy achievement. Genetic engineering is the key technology for converting flower color and it became possible after the discovery of genes involved in anthocyanin biosynthesis and elucidation of their expression mechanisms.

Additionally, color may act as a "fingerprint" of a food product, being related to its flavor and at the same time [149] an estimate of its overall quality. In this sense, special attention is paid to the application of anthocyanin analysis in classification of wine [150]. Anthocyanins can be used as markers to classify wines according to the grape variety [49, 151], although this requires a complex separation with very high chromatographic efficiency, together with advanced statistical methods, especially when dealing with aged red wines, because of the formation [152] of pyranoanthocyanins (formed through the reaction of anthocyanins with small molecules).
