Estimation of stability of anthocyanins acylated with malonic acid

Abstract

In the paper the method of reversed-phase HPLC was used to evaluate the stability of three derivatives
of anthocyanins from the extract of purple corn husk, acylated by malonic acid: cyanidin-3-(3”,6”-
dimalonylglucoside), cyanidin-3-(6”-malonylglucoside), cyanidin-3-(3”-malonylglucoside) regarding the loss
of malonic acid moiety. The purified compounds were obtained by semi-preparative reversed phase HPLC;
two series of solutions were stored at room temperature and in refrigerator (4oC). The solutions were periodically
analyzed by HPLC, while the three above mentioned compounds with addition of cyanidin-3-glucoside
were separated to estimate simultaneously the concentrations, believed to be proportional to peak areas. The
data for all the cases fit first order reaction for anthocyanins concentration in spite of not careful temperature
control for room temperature storage. The rate of anthocyanins hydrolysis dropped in the series: cyanidin-3-
(3”,6”-dimalonylglucoside), cyanidin-3-(6”-malonylglucoside), cyanidin-3-(3”-malonylglucoside), while the
sum of rate constants for last two substances is closed to the rate constant for the first compound. The withdrawal
of the acid moiety form position 6” happened easily then from position 3”. So the ratio of acylated
and non acylated anthocyanins may be changed at not properly storage. It was established that the time required
for hydrolysis of half of the initial acylated anthocyanin at room temperature is 30, 45 and 80 days for
compounds listed above, respectively. In the case the storage in refrigerator (+4oC) the rate of hydrolysis is
reduced by about 5 times.