The influence of tannin preparations on the content and form of anthocyanins of model wine systems in the conditions of induced oxidation

The article considers how oenological tannins effect on the content of anthocyanins, phenolic substances, and their forms that influence the stability of the colour of rosé and red wines. The research material was wine model systems that underwent induced oxidation for a week at a temperature of 45±5 °C with limited access of air. Tannins of different botanical origin were used in the study: hydrolyzable ones – Oaktan FU (oak wood), Tannal W4 (Tara pods), CW Tannal (chestnut wood), and Tannal W2 (gallnuts); and condensed ones – Tannin WG (grape stones), Taniraisin (grape skin), Tannal QW (quebracho wood). The source of anthocyanins was an alcohol extract from the skins of European red grapes. It was obtained by 24 hours long extraction with ethyl alcohol, and with the addition of hydrochloric acid (0.01%). It has been determined that in the course of induced oxidation, the content of phenolic compounds tends to decrease in a wavelike manner in all samples. The anthocyanin content reduces intensively and becomes practically twice as low on the first day of oxidation. The total amount of phenolic compounds becomes 2 to 6 times lower depending on the variant of the experiment. It has been established that condensed tannins of grape origin contribute to the preservation of the total content of phenolic substances (including anthocyanins) in wine, unlike hydrolyzable tannins obtained from other plants. But their application leads to polymerization of anthocyanins, which will result in the appearance of yellow-brown pigments in the red colour of wine. Hydrolyzable tannins obtained from gallnuts and tara trees preserve the red colour of wine for a long time, unlike condensed tannins, due to their antioxidant capacity. Hydrolyzable tannins obtained from tara and quebracho trees will help obtain wine with rich red shades.