How does the use of surfactants in polymer-salt based aqueous twophase systems affect the annatto dye (Bixa orellana L.) partitioning?

Abstract

In this work, the partitioning of natural annatto pigments in aqueous two-phase systems formed by poly(ethylene) glycol polymers (1500 or 4000 or 6000 g mol−1) or triblock copolymer L35 (2000 g mol−1) + sodium citrate + water was studied in the presence of cetyltrimethylammonium bromide. The hypothesis investigated was that the use of surfactants as additives in traditional two-phase aqueous systems could improve the solubility of the annatto extract in the phases of these systems through a mechanism of mixed micelle formation. This would make it possible to implement the use of these systems in the annatto dye extraction process. For this, several experiments were conducted. The annatto extract partition coefficient was determined as a function of pH, surfactant concentration, molar mass and hydrophobicity of the polymer, tie-line length, and the nature of the electrolyte. These results showed the potential of surfactant as a modulation agent for dyes transfer between the aqueous two-phase systems phases. The effect of surfactant was attributed to its interaction with norbixin from annatto, which was studied by means of surface tension and spectrophotometric measurements. The driving force governing annatto extract partitioning was dependent on the system composition and the temperature. Lower partition constants values for annatto extract obtained in the presence of surfactant demonstrated the potential of the aqueous two-phase systems for the extraction or purification of annatto.