What Are Anthocyanins Structure pH Dependent Color Change and Applications
Anthocyanin Definition
Anthocyanins are also known as Anthocyanins. These are water-soluble pigments present in plants, especially in fruits and vegetables. The red, blue, purple, pigments in fruits, vegetables and tubers are due to Anthocyanins. These pigments belonging to the phenol group are in glycosylated forms. When it comes to anthocyanin meaning, the word ‘Anthocyanins’ came from the combination of ‘Anthos’ and ‘Kyanous’. The former implies flowers whereas the latter signifies dark blue colour.
Most of the red, blue, purple flowers contain Anthocyanins. For example, red hibiscus, red roses, pink blossom, blue rosemary, blue chicory, purple sage, purple mint, lavender are edible. Some of these are commonly used as food, colourants and as folk medicine too.
What Is Anthocyanin?
Anthocyanin is a sub-division of phenolic phytochemicals. It is mostly found in the fruits and flowers, particularly their epidermal tissues’ vacuolar sap. Since Anthocyanin is available as a glycoside, you can call it as a glycone. They are a subclass of flavonoids. Thus, they are polyphenols which give the unique colour of the plants or parts of the plants. Apart from normal anthocyanins, Acylated Anthocyanins are also present in plants.
Properties of Anthocyanins
They are responsible for the red, blue or purple colours of vegetable petals, cereals like eggplants, onions, black rice, berries. Along with carotenoids, the autumn leaf colour is partially dependent on the presence of anthocyanins.
Based on their anthocyanin chemistry, they can be classified into two groups, flavonoids and phenolics. These plant pigments are soluble in water.
It has been used as an appetite stimulant, choleric agent and to prevent other diseases as well. Since this is a bioactive component, the bioavailability is the crucial factor for maintaining good health and healing several illnesses.
Source of Anthocyanins
The fruits, vegetables, grains containing anthocyanins are delicious as well as nutritious. Some of the foods that contain Anthocyanins in high amounts are blackberries, purple asparagus, concord grapes, pomegranates, eggplant, raspberries, purple corn, red cabbage, black rice. Still, Anthocyanins are present in fruits and vegetables; they are available in compound forms, not independently. And it is found that the effects are much better when they are consumed in combination with other compounds rather than in isolation. More research is still required to explore different aspects of Anthocyanins.
Uses of Anthocyanins
Anthocyanins have a vast area of applications.
The red, blue or purple pigments extracted from the plants are widely used as dye or food colourant. For instance, Anthocyanin extracted from grape skin is heavily used for adding attractive colours to fruit jams, beverages, or confectionaries.
Several anthocyanin-rich flowers and fruits are used as medicines for treating different ailments. They possess various properties like anti-microbial, anti-cancer, anti-inflammatory, anti-diabetic, as well as anti-obesity. They are also highly effective for the prevention of cardiovascular disease (CVDs). Hence Anthocyanins are potential pharmaceutical ingredients having great medicinal values.
Since people are now concerned about the toxic effects of synthetic food pigment, the demand for plant-based colourants like Anthocyanins is increasing rapidly in the food industry.
The Basic Anthocyanin Structure and Anthocyanin Formula
(Image to be added soon)
This picture depicts the structure of anthocyanins.
The structure of anthocyanin has come from flavylium ion and its basic formula is C15H11O+..
Therapeutic Effects
Anthocyanins are known for their therapeutic effects in different diseases.
Anticancer: Anthocyanins have been studied extensively for treating cancer as well as antiangiogenesis. Antiangiogenesis is a method that stops new blood cell formation that sends oxygen to the tumour cells. It helps in developing cancerous cells. The study for particularly these diseases is based on models of animals along with in-vitro and cell structure.
Anti-diabetic: Anthocyanins are widely used for treating diabetes as in many research, it is seen that anthocyanin-rich Cornus fruits work fantastic in diabetes treatment. For this reason, consumption of Cornus fruits has been prescribed in traditional diabetes treatment in China since ancient times. In studies, noticeable improvement has been seen due to the consumption of anthocyanin-rich fruits for eight weeks at one go.
Anti-obesity: Anthocyanins have potential to fight against obesity. According to a study, the inclusion of purple corn in a regular diet for 12 weeks helps to reduce body weight as well as the weight of white and brown adipose tissues also decreases.
FAQs on Anthocyanins Structure Color Chemistry and Functions
1. What are anthocyanins in chemistry?
Anthocyanins are water‑soluble plant pigments belonging to the flavonoid class that give red, purple, and blue colors to many fruits and flowers. Chemically, they are glycosides of anthocyanidins, meaning a sugar molecule is attached to a colored aglycone structure. Their core structure is based on the flavylium cation (C15H11O+), which is responsible for their color and pH-sensitive behavior. Anthocyanins are commonly found in berries, red cabbage, grapes, and purple corn.
2. What is the basic chemical structure of anthocyanins?
The basic chemical structure of anthocyanins consists of a flavylium ion core attached to one or more sugar molecules. Structurally, they contain:
- A C6–C3–C6 carbon skeleton typical of flavonoids.
- Two aromatic rings (A and B) connected by a three‑carbon heterocyclic ring (C).
- A positively charged oxygen in the C ring forming the flavylium cation.
- One or more sugars (such as glucose) attached via a glycosidic bond.
The variation in hydroxyl (–OH) and methoxy (–OCH3) groups on the rings leads to different types of anthocyanins and color variations.
3. How do anthocyanins change color with pH?
Anthocyanins change color with pH because their molecular structure shifts between different ionic forms depending on hydrogen ion concentration. At different pH values:
- Acidic solution (pH < 3): Red color due to the flavylium cation.
- Neutral pH (~7): Purple due to formation of a quinonoidal base.
- Basic solution (pH > 8): Blue to green due to further structural changes and possible ring opening.
This pH-dependent color change makes anthocyanins useful as natural acid–base indicators, similar to litmus.
4. What is the difference between anthocyanins and anthocyanidins?
The key difference is that anthocyanidins are the aglycone (sugar‑free) forms, while anthocyanins are their glycosylated derivatives. Specifically:
- Anthocyanidins: Basic flavylium structure without sugar.
- Anthocyanins: Anthocyanidins bonded to one or more sugars via glycosidic bonds.
The attached sugar increases water solubility and stability, making anthocyanins more common in plant tissues than anthocyanidins.
5. What are the main types of anthocyanins?
The main types of anthocyanins are classified based on their parent anthocyanidins, such as cyanidin, delphinidin, pelargonidin, peonidin, petunidin, and malvidin. These differ in:
- The number and position of hydroxyl (–OH) groups.
- The number and position of methoxy (–OCH3) groups.
For example, cyanidin-based anthocyanins are common in red berries, while delphinidin derivatives are often responsible for blue and purple hues.
6. Why are anthocyanins considered natural pH indicators?
Anthocyanins are considered natural pH indicators because their color visibly changes in response to hydrogen ion concentration. In aqueous solution:
- They appear red in acidic conditions.
- Purple near neutral pH.
- Blue or green in basic conditions.
This behavior results from reversible structural transformations of the flavylium ion, making red cabbage extract a common laboratory demonstration of acid–base chemistry.
7. How are anthocyanins extracted in the laboratory?
Anthocyanins are extracted by soaking plant material in an acidified polar solvent such as ethanol or water. The basic steps are:
- Crush or grind the colored plant material (e.g., red cabbage or berries).
- Add acidified ethanol (ethanol + small amount of HCl) to stabilize the flavylium form.
- Filter to remove solid residues.
- Collect the colored filtrate containing dissolved anthocyanins.
Acidification prevents degradation and maintains the red flavylium cation structure during extraction.
8. What functional groups are present in anthocyanins?
Anthocyanins contain several important functional groups, including phenolic hydroxyl (–OH), methoxy (–OCH3), ether (C–O–C), and glycosidic linkages. Specifically:
- Aromatic rings with multiple –OH groups.
- A positively charged oxygen in the flavylium cation.
- Sugar units attached through O‑glycosidic bonds.
These functional groups determine their solubility, antioxidant properties, and pH-dependent color changes.
9. What is the role of anthocyanins in plants?
Anthocyanins primarily function as pigments and protective compounds in plants. Their roles include:
- Attracting pollinators with bright red, purple, or blue colors.
- Providing UV protection by absorbing high‑energy light.
- Acting as antioxidants to reduce oxidative stress.
From a biochemical perspective, they are secondary metabolites derived from the phenylpropanoid pathway.
10. Are anthocyanins soluble in water or nonpolar solvents?
Anthocyanins are highly soluble in water and other polar solvents due to their ionic and hydroxyl-rich structure. Their solubility is explained by:
- The presence of multiple –OH groups that form hydrogen bonds with water.
- The positively charged flavylium ion.
- Attached sugar molecules that increase polarity.
They are generally poorly soluble in nonpolar solvents such as hexane because they lack extensive nonpolar hydrocarbon regions.
