Abstract/Summary

The extraction kinetics of betalains (betacyanin and betaxanthin) from freeze dried beetroot powder into aqueous ethanol solutions is modelled by considering the concentration of a given betalain at any given time to result from a balance between the rate of its release from the solid phase and the rate of its chemical degradation in the extract phase. The mathematical model obtained shows that the concentration of the betalain peaks before progressively decreasing with time. The model was experimentally validated for various combinations of temperature (55-85 °C), ethanol concentration (10-30%) and particle size (120-300 µm). The ratio of betacyanin to betaxanthin in the liquid phase was approximately 1 over the duration of extraction at 55 and 65 °C. However, the ratio decreased at the higher temperatures of 75 and 85 °C. A maximum productivity rate of a given betalain was defined as its peak concentration divided by the time taken to reach the peak concentration, which was found to be relatively insensitive to the ethanol concentration below 75 °C.