Anthocyanins: Sources, Structures, and Potential Health Benefits

Anthocyanins are water-soluble natural pigments widely distributed in plants and are an important subclass of flavonoids. They contribute to the red, purple, and blue colors of many fruits, vegetables, and flowers. Beyond their role as natural colorants, anthocyanins have attracted considerable scientific interest because of their antioxidant properties and potential applications in food, nutrition, and skincare. This article introduces the major types of anthocyanins, their chemical structures, and their distribution in various plant foods, including black goji berries, maqui berries, blueberries, black rice, purple sweet potatoes, and grapes. It also explains the structural differences between anthocyanins and proanthocyanidins, outlines their applications as food colorants, and reviews research into their potential biological activities, including antioxidant effects, exercise-related oxidative stress, eye health, and skin protection. In addition, the article discusses the structural modification of anthocyanins, particularly acylation, as a potential approach to improving their stability and physicochemical properties. Finally, it addresses dietary safety considerations and practical measures for preserving anthocyanins during food storage and preparation. Although existing research highlights several promising properties, anthocyanin content varies considerably among food sources, and findings regarding biological activity should be interpreted in light of the available evidence. Understanding their chemical characteristics, natural sources, and limitations is essential for their responsible application in food and health-related products.

The vibrant colors of blueberries, blackberries, purple sweet potatoes, black goji berries, and other deeply colored plant foods are more than just an attractive feature. They are partly attributable to anthocyanins, a group of naturally occurring pigments that have become an important subject of research in food science, nutrition, and plant chemistry.

Anthocyanins are valued not only for their contribution to plant coloration but also for their potential antioxidant properties and possible applications in food coloring, nutritional products, and skincare formulations. However, their composition, stability, and biological activity differ depending on their molecular structure and natural source. Their relationship with another group of plant polyphenols, proanthocyanidins, also deserves attention because the two are related in chemical origin but are not the same compounds.

This article examines where anthocyanins occur in nature, how their structures determine their properties, how they differ from proanthocyanidins, and what current research suggests about their applications and potential health-related functions.

1. Where Are Anthocyanins Found?

Anthocyanins are a class of water-soluble natural pigments widely distributed in plants and represent an important branch of flavonoid compounds. They are found mainly in plant stems, leaf cells, fruit cell sap, and flower petals. More than 200 anthocyanins have been identified in angiosperms, also known as flowering plants, across 27 families and 73 genera. Their concentrations vary considerably according to plant variety, season, climate, maturity, and other factors [1].

Among the more than 200 known anthocyanins, six are particularly important and widespread: pelargonidin (Pg), cyanidin (Cy), delphinidin (Dp), peonidin (Pn), petunidin (Pt), and malvidin (Mv). These six anthocyanidins account for more than 90% of the total anthocyanin pigments found in nature and are core components responsible for plant coloration, particularly in flowers and fruits.

Fruits and other plant foods rich in anthocyanins include black goji berries, maqui berries, blueberries, bilberries, purple sweet potatoes, grapes, blood oranges, pomegranates, eggplants, red cabbage, cherries, strawberries, mulberries, and hawthorn. This distribution indicates that anthocyanins can be extracted from many vividly colored plant fruits and other tissues.

From a structural perspective, anthocyanins belong to the flavonoid family. Their molecular structure is based on a 2-phenylbenzopyrylium cation core, consisting of two benzene rings (rings A and B) and an oxygen-containing heterocyclic ring (ring C). They also contain multiple hydroxyl substituents and a conjugated double-bond system (Figure 2). Differences in the substituents attached to the three rings of the basic C6 (ring A)–C3 (ring C)–C6 (ring B) skeleton determine the specific types of anthocyanins.

Basic structure of anthocyanins. R1 and R2 are H, OH, or OCH3; R3 is H or a sugar group; and R4 is OH or a sugar group.

Anthocyanins can also be regarded as polyhydroxyphenolic compounds. Their stability is influenced by the number and arrangement of hydroxyl groups, and stability may decrease as the number of hydroxyl groups increases. Variations in substituents and bonding patterns, including hydroxyl, methoxy, and sugar groups, give rise to numerous anthocyanin structures. Figure 3 presents the detailed molecular structures of the six most important anthocyanidins found in nature.Detailed molecular structures of the six most important anthocyanidins found in nature. Source: Microsoft Bing.

2. Anthocyanins in Plant Fruits

Individual plant fruits generally contain multiple anthocyanins rather than just one, although the relative abundance of each compound varies. For example, bilberries contain delphinidin, cyanidin, peonidin, petunidin, and malvidin; black chokeberries contain cyanidin and pelargonidin; and maqui berries contain delphinidin and cyanidin.

Black goji berries, sometimes referred to as the “king of anthocyanins,” are notable for their deep color and high anthocyanin content. They grow in arid regions of western China, particularly on the Qinghai–Tibet Plateau. The anthocyanin content of dried black goji berries (left in Figure 4) is typically between 2.5% and 4.8%. This content depends primarily on growing conditions, variety, and maturity. Wild black goji berries growing at high altitudes in dry regions exposed to intense ultraviolet radiation may synthesize more anthocyanins in response to environmental stress.

Maqui berries are another notable source of anthocyanins. Maqui is a perennial plant native to the Patagonian region of Chile in South America. In late autumn, the plants produce clusters of deep-purple berries (right in Figure 4). The Patagonian region extends toward the southernmost parts of South America and includes environments with strong sunlight and substantial exposure to solar radiation. These environmental conditions may influence the production of anthocyanins and other compounds involved in plant protection. Maqui berries have been reported to contain particularly high concentrations of anthocyanins compared with many other fruits.

 Anthocyanin content and characteristics of selected foods

Food	Anthocyanin content (mg/100 g)	Major anthocyanins	Other characteristics
Black goji berries	≤3,690	Cyanidin, delphinidin, pelargonidin, petunidin, and others	Cyanidin is one of the major anthocyanins in black goji berries and has antioxidant properties. Delphinidin is also present in relatively high amounts and has been investigated for its free-radical-scavenging and anti-inflammatory activities. Peonidin may contribute to antioxidant activity alongside other anthocyanins. More than 20 anthocyanin-related compounds, including pelargonidin and petunidin derivatives, have been detected in black goji berries. Cyanidin-3-glucoside is among the most extensively studied active constituents. Black goji berries also contain minerals such as calcium, magnesium, and zinc, as well as vitamins C and E.
Maqui berries	≤2,200	Delphinidin	Delphinidin-3,5-diglucoside is described as a major active constituent, accounting for approximately 80%, alongside other delphinidin derivatives such as delphinidin-3-sambubioside-5-glucoside. These glycosylated structures contribute to the berries' antioxidant properties. Their reported oxygen radical absorbance capacity (ORAC) has been described as 20–30 times that of blueberries.
Black sesame	≤740	Delphinidin	The table identifies anthocyanin glycosides as the main compounds and attributes potential hair and skin benefits to their nutritional properties.
Black rice	≤740	Cyanidin, petunidin	Anthocyanins occur in forms such as cyanidin-3-glucoside. Black rice is also rich in dietary fiber, B vitamins, and minerals.
Blueberries	200–500	Delphinidin and petunidin	Anthocyanin concentrations vary significantly among cultivars. Highbush blueberries generally contain more anthocyanins than lowbush blueberries. Blueberry anthocyanins have been investigated for their potential effects on retinal cells, vision, and eye health.
Mulberries	200–260	Cyanidin derivatives	Cyanidin-3-glucoside accounts for approximately 79%, while cyanidin-3-rutinoside accounts for approximately 19%. Mulberries have also been studied for potential immune-related, digestive, and skin-related benefits.
Purple sweet potatoes	20–100	Cyanidin and peonidin	Anthocyanins commonly occur as glycosides, including cyanidin-3-glucoside and peonidin-3-glucoside. They are often present as acylated anthocyanins, which may improve stability. Acylation with organic acids such as ferulic acid or caffeic acid may influence their stability and antioxidant properties.
Red cabbage	90–300	Cyanidin	Cyanidin-3-glucoside is identified as an important pigment contributing to its purple coloration. Red cabbage is also rich in vitamins C and K and dietary fiber.
Black grapes	≤160	Cyanidin derivatives	Anthocyanins are found mainly in the skin and dark-colored pulp. The source text identifies cyanidin-3-O-glucoside and related compounds among the relevant pigments. Grapes also contain other polyphenols associated with antioxidant activity.
Purple eggplant	20–100	Delphinidin derivatives	Chlorophyll and anthocyanins contribute to eggplant coloration, with anthocyanins playing a major role in the purple skin. Delphinidin-3-glucoside is identified as a principal form. During development, chlorophyll content decreases while anthocyanin content increases.
Cranberries	60–150	Cyanidin derivatives	Cyanidin-3-galactoside is identified as a major form. Cranberries are low in calories and contain dietary fiber, vitamins, and minerals. Their potential relevance to urinary tract health has also been studied.
Cherries	80–300	Cyanidin derivatives	Anthocyanin content generally increases as cherries mature. Cyanidin-3-glucoside is a major form, and cherries also contain other polyphenols, including flavan-3-ols and hydroxycinnamic acids.
Strawberries	7–30	Pelargonidin and cyanidin	Pelargonidin-3-glucoside is the predominant strawberry anthocyanin, accounting for approximately 70% of total anthocyanins. Strawberries also contain cyanidin-3-glucoside and related derivatives.

3. Anthocyanins and Proanthocyanidins

Anthocyanins and proanthocyanidins (PCs) may be considered chemical relatives, but they are two distinct groups of compounds. Proanthocyanidins, also called condensed tannins or, in some contexts, leucoanthocyanidins, are more appropriately classified as polyphenols. Structurally, they can be described as compounds formed by two or more catechin and epicatechin units linked through covalent bonds, commonly involving carbon atoms at positions 8 and 4 (Figure 5). Proanthocyanidins can therefore also be regarded as polymers of flavonoid units.

According to the degree of polymerization, dimers to tetramers are commonly described as oligomeric proanthocyanidins (OPCs), while pentamers and larger polymers are referred to here as polymeric proanthocyanidins (PPCs). The water solubility of proanthocyanidins generally decreases as the number of structural units increases, and lower-degree oligomers are often considered more readily absorbed by the human body.

Chemical structures of proanthocyanidins, where n = 0, 1, 2, …

Structurally, catechin and epicatechin are derivatives of flavanols. Both the C2 and C3 carbon atoms of flavanol molecules are chiral centers. If stereochemistry is disregarded, the molecular structures of catechin and epicatechin can be difficult to distinguish. Their difference lies in the relative spatial orientation of the hydroxyl group at C3 and the phenyl group at C2: in catechin, these groups are on opposite sides in the conventional structural representation, whereas in epicatechin, they are on the same side. Figure 6 shows the chemical structures of flavanol, catechin, and epicatechin.

Chemical structures of flavanol, catechin, and epicatechin.

Because each molecule contains two chiral carbon atoms, catechin and epicatechin have stereoisomeric forms. The form that rotates plane-polarized light clockwise is designated (+)-catechin, while the form that rotates it counterclockwise is designated (−)-catechin. Epicatechin likewise has different stereoisomeric forms. Catechins are important components of tea polyphenols, and the term is also commonly used when referring collectively to flavanols in tea.

Although catechin and epicatechin differ structurally from anthocyanins, there is a chemical relationship between these compounds and anthocyanins, particularly because proanthocyanidins can release anthocyanidins when heated under acidic conditions, as illustrated in Figure 7. This reaction helps explain the origin of the term “proanthocyanidins,” which refers to their capacity to yield anthocyanidins under appropriate conditions.

Thermal decomposition of dimeric proanthocyanidins under acidic conditions.

Proanthocyanidins are not a single compound but a broad group of flavonoid polyphenols widely distributed in plants. They are found in plant skins, shells, seeds, kernels, flowers, and leaves. Grape seeds, for example, are a well-known source of proanthocyanidins.

The antioxidant properties of proanthocyanidins are associated with their functional hydroxyl groups (–OH) and the positions of these groups on the flavonoid rings. Their antioxidant activity is also partly dependent on the degree of polymerization.

4. Applications and Potential Functions of Anthocyanins

4.1. Use as Food Colorants

Many natural materials, including flowers, fruits, nuts, seeds, and tree bark, contain anthocyanins. These compounds contribute to the colors of a wide variety of foods and have attracted interest because of their potential nutritional properties.

One important application is food coloring. Anthocyanins can serve as natural colorants, imparting vivid red, purple, or blue hues to foods and beverages and improving their visual appeal. Their contribution to the colors of certain candies and drinks is one example, although synthetic colorants may also be present.

Compared with synthetic colorants, anthocyanins as natural colorants may better meet consumer demand for ingredients of natural origin and products perceived as more compatible with clean-label and health-oriented food trends. Their suitability for a particular application nevertheless depends on factors such as stability, processing conditions, and the characteristics of the food matrix.

4.2. Potential Biological and Health-Related Functions

From a scientific perspective, the value of anthocyanins extends beyond their role in providing color. Their potential effects on physiological processes have attracted considerable research interest.

Reactive oxygen species (ROS), which are natural by-products of oxygen metabolism, can damage cellular structures when present in excessive amounts. Anthocyanins contain phenolic hydroxyl groups and a pyran ring structure that can contribute to their ability to donate hydrogen atoms and directly scavenge certain reactive oxygen species or free radicals.

Research has described several mechanisms through which anthocyanins may help reduce oxidative damage: (1) interfering with reactions involving the body and superoxide-related species; (2) chelating certain metal ions, thereby limiting the formation of hydroxyl radicals; (3) inhibiting lipid peroxidation, including the formation of malondialdehyde; and (4) interacting with collagen proteins to form a protective barrier that may help limit tissue exposure to external oxidative factors.

Furthermore, as exercise duration and intensity increase, excessive accumulation of reactive oxygen species can disrupt redox balance and reduce the activity of endogenous antioxidant enzymes, contributing to oxidative stress. Anthocyanins have been investigated for their potential to alleviate exercise-associated oxidative stress. They have also been studied for possible effects on rhodopsin regeneration and ocular microcirculation, which may be relevant to eye comfort during prolonged visual activity.

Delphinidin, found in blueberries, raspberries, and purple eggplant skin, has been reported to exhibit antioxidant activity. One source reports that its antioxidant capacity is approximately 50 times that of vitamin E and 20 times that of vitamin C. Delphinidin is thought to scavenge superoxide anions and free radicals primarily through hydrogen-atom transfer mechanisms.

Purple sweet potato anthocyanins have demonstrated scavenging or inhibitory effects against reactive oxygen species, including hydroxyl radicals (•OH) and hydrogen peroxide (H₂O₂), with particularly strong reported activity against hydroxyl radicals compared with ascorbic acid. Research has also investigated pelargonidin-3-O-glucoside (Pg3G) derived from blueberries for its antioxidant and potential blood-glucose-regulating activities.

Major potential biological and health-related functions of anthocyanins.

In recent years, chemists have used molecular modification techniques to acylate certain anthocyanins and develop enzymatic methods for synthesizing acylated anthocyanins. Enzymatic synthesis systems have been established and optimized using Pg3G and various organic acids, including acetic acid, malic acid, and succinic acid, to produce a series of acylated Pg3G derivatives.

Research has found that acylated Pg3G exhibits improved lipophilicity. This suggests that acylated anthocyanins may more readily partition into lipid-rich environments and interact with cell membranes. They may also have longer retention times under physiological conditions. Studies have further investigated the mechanisms underlying their improved stability and biological activity. This research may have important implications for the food and pharmaceutical industries.

4.3. Potential Skin Care Benefits

From a chemical perspective, cellular oxidative damage is associated with skin damage and aging. Antioxidant activity is therefore one of the most extensively studied properties of anthocyanins. Proposed antioxidant mechanisms include activation of enzymatic antioxidant systems, reduction of DNA damage, limitation of reactive oxygen species accumulation, free-radical scavenging, and interactions with metal ions.

These mechanisms have prompted interest in the potential role of anthocyanins in protecting skin cells against oxidative stress. Research has investigated whether anthocyanins may help limit oxidative damage associated with skin discoloration, dullness, and age-related changes.

Anthocyanins are often described as powerful natural antioxidants. Their ability to interact with free radicals has led to investigations into their potential anti-aging effects. Long-term dietary intake of anthocyanin-rich foods and the use of anthocyanin-containing cosmetic products have been studied in relation to ultraviolet-induced DNA damage and the development of wrinkles and age spots.

Anthocyanins and related compounds may also influence the degradation of collagen and elastin, which contribute to skin firmness and elasticity. For example, anthocyanins and other flavonoids in purple grapes have been investigated for potential effects on skin wrinkles and related markers of skin aging.

5. Precautions When Consuming Anthocyanin-Rich Foods

Anthocyanins consumed as part of a normal diet are generally considered safe. However, the claim in the source material that the European Food Safety Authority (EFSA) has established a tolerable daily intake (TDI) of 30 mg/kg body weight requires verification against an authoritative EFSA assessment before it is used as a definitive safety limit. Applying that figure to an adult weighing 60 kg would yield 1,800 mg per day, but this calculation alone does not establish an officially recognized safe intake limit for all anthocyanins.

Obtaining anthocyanins from naturally occurring foods is a practical way to include these compounds in the diet. Nevertheless, their content varies considerably among foods, and the safety and effects of concentrated extracts or supplements cannot automatically be inferred from ordinary food consumption.

Anthocyanins are sensitive to environmental factors such as light, temperature, and oxygen, which can reduce their stability. The following measures may help preserve them during storage and food preparation:

1. Protect foods from light. Anthocyanins are sensitive to light, so anthocyanin-rich foods should be stored in a cool place or in sealed containers away from direct sunlight.

2. Limit excessive heating. High temperatures can alter anthocyanin structures and reduce their content. When preparing anthocyanin-rich foods, avoid unnecessarily prolonged or intense heating; cold preparations may be suitable where appropriate.

3. Consider acidity. Anthocyanins are generally more stable under acidic conditions. Adding suitable acidic ingredients, such as vinegar or lemon juice, may help preserve their color and stability during food preparation.

4. Pay attention to metal contact. Certain metal ions can accelerate anthocyanin oxidation or alter their color. Appropriate food-grade utensils and storage containers should be selected to minimize unwanted interactions.

Finally, any dietary or topical use intended to support health should be considered in the context of appropriate amounts and available scientific evidence. Anthocyanins are promising plant compounds, but their potential benefits should not be interpreted as proof that they can treat or prevent diseases.

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