Supercritical CO2 extraction of bioactive Tyrian purple precursors from the hypobranchial gland of a marine gastropod

• Bioactive brominated indole precursors to Tyrian purple can be extracted by CO2 SFE.
• The yields from SFE were comparable to chloroform extraction.
• Varying SFE pressure allows selective extraction of different brominated indoles.
• Toxic choline esters were retained in the tissue and were not present in SFEs.
• SFE provides a viable and safe alternative to chloroform for indole recovery.

Supercritical CO2 provides considerable advantages over traditional solvents for the extraction of bioactive compounds from organic matter. Here we demonstrate the use of supercritical CO2 as an efficient and safe alternative to traditional solvent extraction for the recovery of bioactive Tyrian purple precursors tyrindoleninone, 6-bromoisatin and tyriverdin from the marine mollusc Dicathais orbita. The effect of pressure on the selective extraction of brominated indoles was tested at 15, 30 and 50 MPa CO2, and was compared to traditional chloroform extract composition and yields. Extracts obtained from 15 MPa selectively concentrated 6-bromoisatin, at 78% of the extract composition, whereas increased pressures of 30 and 50 MPa increased the solvating power of supercritical CO2 to include the more lipophilic tyrindoleninone at 35 and 29% respectively, and tyriverdin at 23 and 40% respectively. This extraction method was also effective in separating the brominated indoles from toxic choline esters in the mollusc extracts. Extract yields from supercritical CO2 were comparable to solvent extraction relative to whole whelk weight. This provides a viable alternative for nutraceutical development that does not rely on the use of toxic solvents.

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