Evaluation of colour and stability of anthocyanins from tropical fruits in an isotonic soft drink system

Due to the growing market of food products associated to good health, the colour changes and stability of anthocyanin extracts from acerola, containing high level of ascorbic acid, and from acai, rich in flavonoids, were evaluated in an isotonic soft drink like system and in buffer solution. The degradation of anthocyanins from both sources followed first-order kinetics in all the systems, under air, either in the presence or absence of light. Addition of sugars and salts had a negative effect on the anthocyanin stability, being the rate constant (k(obs)) values in isotonic soft drink system 6.0 x 10(-2) h(-1) for acerola and 7.3 x 10(-4) h(-1) for agai, both in the dark. In the presence of light, the anthocyanin degradation was 1.2 times faster for acerola and 1.6 times faster for agai in soft drink isotonic systems, as compared to their respective buffer solutions. The highest stability observed in all acai systems was correlated to its high total flavonoid content and absence of ascorbic acid. The gradual degradation of red colour during storage of all systems was verified by the decrease of a* values, accompanied with decreased colour intensity (decrease in C* values) and tonality changes from red to yellow colour, as the h values increased during the experiment time. (c) 2007 Elsevier Ltd. All rights reserved.