Aqueous two-phase extraction: A non-thermal technique to separate and concentrate betalains from Bougainvillea glabra Choisy bracts

Abstract

The purple bracts of Bougainvillea glabra Choisy contain betalains that can be used as pigmenting agents. The objective was to evaluate the use of aqueous two-phase extraction systems to separate betalains from B. glabra bracts in order to improve the potential of this species as a source of natural pigments. A binodal phase diagram for the mixture of polyethylene glycol 4000 (PEG 4000) and trisodium citrate (Na3Cit; Na3C6H5O7) was studied to select betalain extraction conditions. The separation and concentration of betalains was evaluated and the feasibility of partitioning into betacyanins and betaxanthins was assessed. Mixtures of Na3Cit and PEG 4000 were prepared with concentrations in the ranges of 3.02–39.69% and 0.28–36.98%, respectively, and formed aqueous biphasic systems, with top phases composed mainly by PEG 4000 and bottom phases composed mainly by Na3Cit. The betalains showed a tendency to migrate towards the top phase, with an average separation yield of 92.41% and a concentration of 176.57 mg/L, while in the bottom phase an average content of 4.53 mg/L was found. Such situation was caused by a salting-out phenomenon and by a non-thermal concentration of compounds given by a reduction of the volume ratio between phases. The partition coefficient varied between 18.95 and 183.4 in betacyanins (Bc) and between 6.85 and 80.0 in betaxanthins (Bx). The Bc/Bx ratio varied between 2.82 and 3.26 in top phases and between 1.26 and 1.45 in bottom phases. The use of aqueous two-phase extraction systems allowed betalains to be separated and concentrated, although only a partial partitioning of Bc and Bx was achieved.