Influence of chemical structure of alcohols on extraction and stability of anthocyanins.

Вплив хімічної будови спиртів на екстракцію і стабільність антоціанів

Introduction. The aim of this research was to evaluate the efficiency of the anthocyanin extraction from grape skins with different alcohols under different conditions such as temperature and pH. Materials and methods. Grape pomace of red grapes of the Vitis Vierul variety, which are obtained after the production of wine by white way and are considered as winemaking waste, were studied. The mass concentration of the anthocyanins was measured by pH differential spectrophotometry and expressed in mg of equivalent cyanidin-3-glycoside per gram of dry matter. The rate constant and half-life of the anthocyanin degradation were calculated for a temperature of 60 °C. Results and discussion. The effect of pH and the chemical structure of the molecule of alcohol extractant on the efficiency of anthocyanin extraction and its spectral characteristics was studied. The number of hydroxyl groups in the alcohol used as extractant as well as the length of the hydrocarbon moiety had a key role in the process efficacy. In particular, for monohydric alcohols, the efficacy follows the order: 2-methylpropan-1-ol < butan-1-ol < propan-2-ol < ethanol < methanol. On the other side, increasing the number of OH groups in the line ethanol - ethane-1,2-diol - propane-1,2,3-triol does not enhance the extraction performance. The spectral characteristics of extractions obtained with ethanol and polyhydric alcohols are similar, the absorption maximum is unclear and is in the range of 530-560 nm. When the length of the carbon chain of alcohol increases, the electronic absorption spectra are characterized by different intensity and a wide, indistinct absorption maximum. The thermal stability of anthocyanins in the extracts was determined by the rate constant of the anthocyanin degradation reaction and the half-life. Decreasing the pH of the extract leads to an increase in the thermal stability of anthocyanins. Ethanol is the best extractant in terms of the technological and economic efficiency of natural pigment extraction and for its application in the food industry. Anthocyanin half-life in ethanol is about 10 hours at 60 °C that indicates its suitability to be used in industrial processing. Conclusions. The results obtained make it possible to evaluate the efficiency of the extraction of anthocyanins with alcohols from grape skins and their thermal stability. [ABSTRACT FROM AUTHOR]