Impact of the extraction procedure on the kinetics of anthocyanin and colour degradation of roselle extracts during storage.

BACKGROUND

The stability of anthocyanins and colour of aqueous extracts from roselle (Hibiscus sabdariffa L.) was investigated during storage at 4-45 °C. The effect of the extraction procedure (cold or hot extraction with or without pasteurisation) on the kinetic behaviour was determined.

RESULTS

Data analysis showed first-order kinetics for the evolution of anthocyanin content, colour density, colour strength and browning index. Three models (Arrhenius, Eyring and Ball) were used to represent the temperature dependence of the reaction rates. The three models allowed the prediction of colour modifications according to the storage temperature over 6 months. Activation energies ranged from 22 to 26 kJ mol(-1) for anthocyanin degradation and from 18 to 34 kJ mol(-1) for colour parameter modification. The degradation rate during storage depended on the extraction procedure. When heated, the extracts were clearly less stable. Their colour changed faster during storage especially when hot water and pasteurisation were used.

CONCLUSION

Although the anthocyanin content and initial colour were not modified, the extraction conditions, especially temperature, greatly affected the stability of the extracts during storage. Further studies are needed to understand the mechanisms involved.