Some regularities in the process of anthocyanin extraction from vegetable sources

Abstract

This work investigates regularities in the process of extracting anthocyanins from various plant sources in the medium of extractants. For extraction, fresh plant samples were used, including the roots of purple carrots, roots of purple potatoes of the Amethyst variety, fresh fruits of Michurin's aronia, fruits of the garden nightshade, cornelian cherries, blueberries and red cabbage, as well as dried peony petals. The extraction was carried out by infusing the plant material under study in a selected extractant (left overnight). The concentration of anthocyanins was determined spectrophotometrically. It was shown that a 0.1 M aqueous solution of HCl is an effective and environmentally friendly extractant allowing for the extraction of anthocyanins from various sources. Provided that the medium acidity is greater than 1, significant losses of anthocyanins are possible: 5-45% at pH = 2; 33-88% at pH = 3; 41-92% when extracted with distilled water. Acylation does not contribute to an increase in the degree of anthocyanin extraction. The addition of organic solvents (ethanol, acetonitrile and glycerin) can significantly accelerate the anthocyanin extraction in some cases, which is particularly true for cornelian cherries. When using crushed material, the influence of the extractant on the degree of extraction is minimal. Information is presented on the solvatochromic effect, which affects the spectral characteristics of some anthocyanin solutions. It was shown that the shift of the absorption band maximum is the greatest for non-acylated anthocyanins, while decreasing for acylated compounds. The latter is most likely to be associated with the intramolecular copigmentation of acylated anthocyanins in aqueous solutions. When determining the concentration of anthocyanins in solvents with different concentrations of organic additives, the solvatochromic effect should be taken into account. The addition of an organic solvent leads not only to a shift in the absorption band maxima, but also to significant hyperchromic effects. If this effect is ignored, errors in determination of anthocyanins can exceed 70%. This paper proposes a simple and effective approach to considering these effects using a cross-dilution scheme. Therefore, the choice of extractants for efficient anthocyanin extraction from various plant raw materials was experimentally substantiated, and a method for evaluating solvatochromic effects was proposed.