Co-precipitation of carotenoids and bio-polymers with the supercritical anti-solvent process

Carotenoids are widely used as natural colorants in food or pharmaceutical industries. In some industrial formulations, these carotenoids are mixed with bio-polymers, to improve the stability of the carotenoid, its dissolution rate in water, and to make the dosage and the handling of the product easier. The supercritical anti-solvent (SAS) process is specially suitable for the production of fine powders of these mixtures, as it yields solvent-free products with a reduced thermal degradation or oxidation of the carotenoids. In this work, the application of the SAS process to the precipitation of β-carotene or lutein with poly-ethylene glycol (PEG) has been studied. The influence of different process parameters, including the operating pressure and temperature, the polymer/carotenoid concentration ratio, and the CO2 flowrate have been studied experimentally. Additionally, a phase equilibrium model of these systems based in the perturbed hard-sphere-chain equation of state (PHSC EoS) has been developed. This model is helpful for the analysis of the experimental results. In particular, this model predicts the apparition of a liquid–liquid immiscibility region at moderate temperatures due to the co-solvent effect of CO2 on PEG. This explains the difficulties found in the precipitation experiments performed at these conditions. The existence of this phase behavior has been corroborated by performing batch gas anti-solvent (GAS) precipitation experiments in a windowed vessel.