Anthocyanins belong to a large group of secondary plant metabolites collectively known as flavonoids, a subclass of the polyphenol family. They are a group of very efficient bioactive compounds that are widely distributed in plant food. Anthocyanins occur in all plant tissues, including leaves, stems, roots, flowers, and fruits. Research on phenolic compounds through the last century, from the chemical, biochemical, and biological points of view, has focused mainly on the anthocyanins. Anthocyanins have structures consisting of two aromatic rings linked by three carbons in an oxygenated heterocycle (i.e., a chromane ring bearing a second aromatic ring in position 2). The basic chromophore of anthocyanins is the 7-hydroxyflavilyum ion. Anthocyanin pigments consist of two or three chemical units: an aglycon base or flavylium ring (anthocyanidin), sugars, and possibly acylating groups. Only six of the different anthocyanidins found in nature occur frequently and are of dietary importance: cyanidin, delphinidin, petunidin, peonidin, pelargonidin, and malvidin. Each aglycon may be glycosilated or acylated by different sugars and aromatic or aliphatic acids, yielding over 600 different anthocyanins reported from plants. The sugar moiety is typically attached at the 3-position on the C-ring or the 5-position on the A-ring. The chromophore of eight conjugate double bonds carrying a positive charge on the heterocyclic oxygen ring is responsible for the intensive red-orange to blue-violet color produced by anthocyanins under acidic conditions. Anthocyanins occur in solution as a mixture of different secondary structures: flavylium ion, a quinoidal base, a carbinol base, and a chalcone pseudobase. Self-association, intermolecular, and intramolecular co-pigmentation of anthocyanins leads to the formation of tertiary structures through varying stabilization mechanisms. Anthocyanin composition has been used as a botanical tool for taxonomic classification of plants. In addition, anthocyanin profiles of fruits and vegetables allow detecting adulteration of anthocyanin-based products and are indicators of product quality. Anthocyanins are common components of the human diet, as they are present in many foods, fruits, and vegetables, especially in berries. Moreover, anthocyanins have an antioxidant activity, depending to a large extent upon their chemical structure. Many epidemiological studies have shown the benefits of a diet rich in fruit and vegetables to human health, and for the prevention of various diseases associated with oxidative stress, such as cancer and cardiovascular diseases. Anthocyanin-rich extracts are increasingly attractive to the food industry as natural alternatives to synthetic FD&C dyes and lakes, because of their coloring properties. Anthocyanins are also one of the nine European Union-designated natural color classes. Various adverse effects on health have frequently been attributed to synthetic antioxidants. For these reasons, currently, there is a trend towards relying on antioxidants derived from natural products. Anthocyanins act as antioxidants both in the foodstuffs in which they are found and in the organism after intake of these foods. This review, like the first one of the series, intends to reflect the interdisciplinary nature of the research that is currently carried out in this prolific area.

This study was designed to determine the contents of total polyphenols, flavonoids, flavonols, flavanols, and anthocyanins of purple corn (Zea mays L.) extracts obtained with different methanol:water concentrations, acidified with 1% HCl (1 N). Another objective was to determine the antioxidant activity by 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), ferric reducing antioxidant power (FRAP), and deoxyribose assay, individual phenolic compounds by high-performance liquid chromatography (HPLC), and endogenous antioxidant enzyme (superoxide dismutase [SOD], catalase [CAT], and total peroxidase [TPX]) activity and lipid peroxidation activity (thiobarbituric acid–reactive substances [TBARS] assay) in isolated mouse organs. Overall, the highest total content of polyphenols, anthocyanins, flavonoids, flavonols, and flavanols was obtained with the 80:20 methanol:water extract, acidified with 1% HCl (1 N). The 50% inhibitory concentration values obtained by the DPPH and ABTS assays with this extract were 66.3 μg/mL and 250 μg/mL, respectively. The antioxidant activity by the FRAP assay was 26.1 μM Trolox equivalents/g, whereas the deoxyribose assay presented 93.6% inhibition. Because of these results, the 80:20 methanol:water extract, acidified with 1% HCl (1 N), was used for the remaining tests. Eight phenolic compounds were identified by HPLC: chlorogenic acid, caffeic acid, rutin, ferulic acid, morin, quercetin, naringenin, and kaempferol. Furthermore, it was observed that the purple corn extract was capable of significantly reducing lipid peroxidation (lower malondialdehyde [MDA] concentrations by the TBARS assay) and at the same time increasing endogenous antioxidant enzyme (CAT, TPX, and SOD) activities in isolated mouse kidney, liver, and brain. On the basis of the results, it was concluded that the purple corn extract contained various bioactive phenolic compounds that exhibited considerable in vitro antioxidant activity, which correlated well with the decreased MDA formation and increase in activity of endogenous antioxidant enzymes observed in the isolated mouse organs. This warrants further in vivo studies with purple corn extracts to assess its antioxidant activity and other bioactivities.

Many epidemiological studies have shown the benefits of a diet rich in fruit and vegetables to human health and for the prevention of various diseases associated with oxidative stress, such as cancer and cardiovascular diseases. Anthocyanins, natural pigments belonging to the group of flavonoids, are common components of the human diet, as they are present in many foods, fruits, and vegetables, especially in berries. Their use as colorants has considerable interest because of their coloring properties. Moreover, they have an antioxidant activity. Various adverse effects on health have frequently been attributed to synthetic antioxidants. For these reasons, currently, there is a trend towards relying on antioxidants derived from natural products. The efficacy of anthocyanins as antioxidants depends, to a large extent, upon their chemical structure. They act as antioxidants both in the foodstuffs in which they are found and in the organism after intake of these foods. With this in mind, an introduction to polyphenols is made with emphasis on their role as secondary metabolites, classification, and health relevance. Flavonoid intake, biological activities, databases, classification and structure, distribution, and dietary sources are then considered. Aspects of anthocyanin concerning its early history and chemical structure, color, and intake are dealt with in the second part of the series. The extraction and analysis of anthocyanin pigments and their antioxidant power, paying special attention to the oxidation process, will be the subject of the third part. Bioavailability and metabolism of anthocyanic pigments, the methods used for measuring the antioxidant activity of anthocyanins, and the influence of anthocyanins on the antioxidant activity of wine will finally be covered in the fourth part. The present review intends to reflect the interdisciplinary nature of the research that is currently carried out in this prolific area. Key research articles and reviews are mainly referenced, and we apologize to those researchers whose work is not cited directly by us.