Stability of betalains extracted from garambullo (Myrtillocactus geometrizans)

The garambullo is a cactus that grows in arid and semiarid zones; it bears a purple fruit which contains pigments belonging to the betalain family. Several extractions of the pigment were performed using different solvents and its stability was evaluated in the presence of stabilizing agents. The major concentration of betalains was extracted with ethanol-HCl (99:1); however, these pigments were more unstable (Delta E = 14.6) as compared with the pigment obtained by an aqueous extraction (Delta E = 12.3). The results showed that the pigment is stable at pH 4.8-5.2 and low temperatures, this was confirmed by the half-life: at 25 degrees C the half-life was 11 413.6 min in comparison with 83.5 min at 60 degrees C. In the presence of 0.1% ascorbic acid the half-life was doubled and the energy of activation was 25.78 kcal/mol compared to 22.07 kcal/mol for the control. Ascorbic acid 0.1% was the best stabilizing agent among the compounds used in the present study of Myrtillocactus geometrizans pigment in aqueous solution at pH 4.8 and 5.2.