Comparative extraction of anthraquinones from madder roots: Kinetics, selectivity and dyeing properties using maceration, ultrasound and supercritical CO₂

Extraction of anthraquinone dyes from madder roots was performed by maceration (MAC), ultrasound assisted extraction (UAE) and CO 2 + cosolvent extraction (SFE) in similar conditions of temperature and solvent (or cosolvent) composition. All processes led to similar extract yields (over 30 g/100g roots ) and anthraquinone recoveries (3.3 – 4.0 g anthra /100g roots ), extracting the five quantified anthraquinones but at different rates. Compared to MAC and UAE, the CO 2 -based extraction process exhibited slower kinetics and revealed selectivity towards anthraquinone glycosides. This could be explained by a possible degradation of glycosidase enzymes during SFE extraction. Regardless of the extraction process, among the identified and quantified anthraquinones, lucidin primeveroside and ruberythric acid were the main compounds extracted. All processes produced an overall extract containing 10-12%w anthraquinones, but with variable glycoside and aglycone proportion. More, overall extract composition was highly different from fraction compositions throughout extraction course. Colours obtained after dyeing silk fabrics with various extracts varied from orange to pink/red according to their composition, especially the ratio between aglycone and glycoside anthraquinones. Thus, the composition of the extract and the shade obtained for the silk can be adjusted through the process.