ABSTRACT
Anthocyanins (ACNs) are water-soluble plant secondary metabolites responsible for the blue, purple, and red color of many plant tissues. They occur primarily as glycosides of their respective aglycone anthocyanidin chromophores (Figure 5.1), with the sugar moiety mainly attached at the 3-position on the C-ring or the 5, 7-position on the A-ring. Glycosylation at 3′, 4′, 5′-position of the B-ring, although very rare, has also been observed [1]. Glucose, galactose, arabinose, rhamnose, and xylose are the most common sugars that are attached to anthocyanidins as mono-, di-, or trisaccharide forms. Aglycones are rarely found in fresh plant materials. There are about 25 different anthocyanidins found in nature [2], whereas only six of them, cyanidin, delphinidin, petunidin, peonidin, pelargonidin, and malvidin, are ubiquitously distributed (Figure 5.1). The differences in chemical structure of these six common anthocyanidins occur at the 3′ and 5′ positions of the B-ring
5.1 Introduction .................................................................................................. 141 5.2 Reactive Oxidants, Antioxidants, and Diseases ........................................... 144 5.3 Antioxidant Capacity of ACNs: Direct Radical Scavenging/Reducing
Capacity ........................................................................................................ 146 5.3.1 Chemical-Based Assays .................................................................... 147 5.3.2 Cell-Based Assays ............................................................................ 148 5.3.3 In Vivo Assessment ........................................................................... 149 5.3.4 In Vitro vs. In Vivo Antioxidant Activity of ACNs: Impact
of Bioavailability .............................................................................. 151 5.4 Antioxidant Activities of ACNs: Indirect Effects ......................................... 152
5.4.1 ACNs and Antioxidant/Oxidant Enzymes........................................ 152 5.4.2 ACNs and Redox Cell Signaling Pathways ...................................... 153
5.5 Antioxidant Activities in Disease Prevention of ACNs ................................ 155 5.5.1 Atherosclerosis .................................................................................. 155 5.5.2 Cancer ............................................................................................... 156 5.5.3 Alzheimer’s Disease ......................................................................... 157
5.6 Concluding Remarks .................................................................................... 158 References .............................................................................................................. 158
(Figure 5.1). The sugar moieties may also be acylated by a range of aromatic or aliphatic acids. Common acylating agents are cinnamic acids (Figure 5.1). For most naturally occurring ACNs, their molecular weights (MW) are within the range of 400-1200, depending on the type of anthocyanidin and the type/number of sugar and acylated groups. Two ACNs, which represent simple or complex ACNs isolated from strawberry or red cabbages, are shown in Figure 5.2. 3-Deoxyanthocyanins are another group of anthocyanidins that do not have a hydroxyl group on 3-position
FIGURE 5.1 Common ACN structures. Sugar moieties are generally on position 3 of the C-ring. Selected sugars that commonly occur in ACN structures.
