A mass transfer model applied to the supercritical extraction with CO2 of curcumins from turmeric rhizomes (Curcuma longa L)

Increasing restrictions on the use of artificial pigments in the food indus try, imposed by the international market, have increased the importance of raw materials containing natural pigments. Of those natural substances with potential applications turmeric rhizomes (Curcuma longa L), are one of the most important natural sources of yellow coloring. Three different pigment s (curcumin, desmetoxycurcumin, and bis-desmetoxycurcumin) constitute the c urcuminoids. These pigments are largely used in the food industry as substi tutes fur synthetic dyes like tartrazin. Extraction of curcuminoids from tu meric rhizomes with supercritical CO2 can be applied as an alternative meth od to obtain curcuminoids, as natural pigments are in general unstable, and hence degrade when submitted to extraction with organic solvents at high t emperatures. Extraction experiments were carried out in a supercritical ext raction pilot plant at pressures between 25 and 30 MPa and a temperature of 318 K. The influence of drying pretreatment on extraction yield was evalua ted analyzing the mass transfer kinetics and the content of curcuminoids in the extracts during the course of extraction. The chemical identification of curcuminoids in both the extract and the residual solid was performed by spectrophotometry. Mass transfer within the solid matrix was described by a linear first-order desorption model, while that in the gas phase was desc ribed by a convective mass transfer model. Experimental results showed that the concentration profile for curcuminoids during the supercritical extrac tion process was higher when the turmeric rhizomes were submitted to a dryi ng pretreatment at 343 K.