Accelerated storage test of betalains extracted from the peel of pitaya (Hylocereus cacti) fruit.

Betalains are nitrogen-containing colorants with antioxidant properties that can be found in plant materials such as pitaya peels. However, thermo-stability of these natural colors may vary with different source, yet few study has reported the rate orders of degradation for pitaya-sourced betalains. In this study, accelerated storage test of betalains, namely betacyanin and betaxanthin, extracted from pitaya peel are investigated by heat treatment of the extract at elevated temperatures. The results show that degradation kinetics of betacyanins and betaxanthins can both fit first-order kinetics and Arrhenius equation with activation energies at - 49.2 kJ/mol and - 40.0 kJ/mol, respectively. The result of Student's t-test indicated that the predicted k values are statistically the same as compared to their corresponding experimental values. LSD estimation also showed that k value variation tendency of the two betalains appears to be the same at 60 °C or below, while betacyanins tend to degrade faster above 80 °C than betaxanthins due to higher coefficient value of k value variation. This result also suggests that the pitaya-sourced betalains tend to degrade gradually even though they are stored under refrigerated condition. However, the betalains showed appreciably lower rate of degradation if they are processed at 60 °C or below.