The influence of pH on the thermal stability of 5-O-caffeoylquinic acids in aqueous solutions

Chlorogenic acid, the ester of caffeic acid with quinic acid, is a natural phenolic compound found in all higher plants. It is potentially useful in pharmaceuticals, foodstuffs, feed additives, and cosmetics due to recently discovered biomedical activity of this compound. This finding caused new interest in the properties of chlorogenic acid in its isomers and in its natural occurrence. It has been found that as many as fourteen compounds (chlorogenic acid derivatives and its reaction products with water) can be formed from 5-O-caffeoylquinic acid by heating its water solution at different pH. Four of them, two hydroxylated 3-O-caffeoylquinic acid derivatives and two hydroxylated 4-O-caffeoylquinic acid derivatives, have been not reported yet. The amount of each formed component depends on the heating time and pH. The transformation product can be mistakenly treated as a new component, not found before in the examined plant, or can be a cause of erroneous quantitative estimations of plant composition.