ANTHOCYANINS – CHEMISTRY AND BIOLOGICAL ACTIVITY

Abstract

Anthocyanins are a group of  over 500 different compounds that cause red, purple and blue colours of many plants, especially fruits, vegetables and cereals. Anthocyanins structuraly belong to flavones. Mainly fruit is considered the main source of anthocyanins , although they are present in vegetables, roots, bulbs, fruit pulps, pulses and cereals. Huge diversity of anthocyanins, which can be found in nature makes them very complex and interesting group. In plants anthocyanins are present in the form of heterosides. Aglycone anthocyanins are known as anthocyanins. In nature there is 6 well known anthocyanins: pelargonidin, cyanidin,  peonidin, delphinidin, malvidin and petunidin . Pelargonidin as stable anthocyanins is the most frequent in nature. The glycoside derivatives of the most widespread in nature are 3-monoside, 3.5 and 3.7 biosides. Interest for anthocyanins is growing over the past few years due to their potential applications in the pharmaceutical industry, the food and cosmetic industries. Despite their great potential, their use is still limited because of their relative instability and the low percentage of extracting from the plant material. Anthocyanins are quite reactive and unstable compounds. They transform reversibly with pH changes. pH is defined as the greatest cause of instability of anthocyanins, and has the greatest impact on colour. Anthocyanins are polar molecules and the most efficient solvent for extraction are the mixture of polar solvent such as ethanol, methanol and acetone. Extraction methods for anthocyanins isolation are not selective because solvents extracted anthocyanins with ballast and the great number of substances such as sugars and organic acids. Because of that, it is necessary to implement a new purification techniques, such as solid phase extraction (SPE), liquid-liquid extraction (LLE), countercurrent chromatography (CCC), and high performance liquid chromatography (HPLC). Identification of anthocyanins play a key role in the taxonomy and evaluate the quality of herbal drugs and foods containing anthocyanins. Reversed phase RP-HPLC connected to a photodiode (DAD detector) is the most used method for detection and identification of anthocyanins. Sample preparation for HPLC analysis usually involves acid hydrolysis of anthocyanins to release anthocyanidins. Anthocyanins may be quantified using any purified standard, but most commonly used is standard of cyanidin-3-glucoside, and quantification is carried out at a wavelength of 520 nm. The method of choice for the rapid screening of total anthocyanins in vegetables and fruits is spectrophotometric determination at 528 nm, with a controlled pH. This method works very well, when the assessment is required and not the accuracy of the quantification. Anthocyanins are poorly absorbed and metabolised to the same extent as other flavonoids, which are considered to have low bioavailability. Examination of bioavailability for most of the anthocyanins was carried out on animals. Most studies have shown maximum concentration in blood after 15min-2h. Interest in anthocyanins has especially grown in recent years due to their positive effects on health. Anthocyanins are effective for chronic diseases, especially in cardiovascular diseases. Together with the other nutritional ingredients are important because of their antioxidant ability, suggesting their potential application in the prevention of several diseases which are associated with oxidative stress. Some plants with high content of anthocyanins play a role in the prevention of mutagenesis and carcinogenesis as inhibitors. Extracts obtained from berries have the highest potential for the removal free radicals. Antioxidant activity of them is proportional to the content of anthocyanins.