A SELECTIVE EXTRACTION OF ANTHOCYANINS FROM EGGPLANT PEEL

The aim of the present study was to develop an inexpensive method for anthocyanin extraction from eggplant peel using tartaric and malic acids solutions as solvents in a discontinuous process, to obtain a natural colorant prototype. The setting of optimal solvent concentration, temperature solvent, time of extraction, solvent/solid ratio as well as the yield and rate of extraction were studied, and comparative tests by acidified ethanol also carried out. Solanum melongena eggplants var. esculentum were purchased from producers from 8 different locations in the Sicilian Ragusa area (Italy). Eggplants were harvested at the commercial ripening stage and stored at 4.0°C for 24 h. Eggplant peel layers with uniform thickness were removed using a sharp knife. The layers were then reduced to 20 mm2 fragments and stored at -20°C.Solvent/solid ratio was varied from 2:1 to 80:1, extraction temperature from 10 to 60°C, extraction solvent concentration from 0.50 to 2.00%, extraction time from 0 to 60 m, in order to define the best extraction conditions. Each extraction was transferred into a dark glass bottle with pumped nitrogen at the same time (a nitrogen sweep was used before and during filling), and then stored at 4.0°C. The extraction was repeated 3 times since by the third extraction 97% had been recovered. A comparative extraction was carried out using acidified alcoholic solvent (ethanol:water:HCl 70:30:1) in order to determine total extractable anthocyanins. Tartaric and malic acids solutions were effective in extracting anthocyanins from fresh eggplant peels. In fact, solutions of the two organic acids employed as alternative solvents showed good extraction yields ( 90% of anthocianins) after 60-80 min. However, extraction by acidified ethanol at solvent/peel=10 appears more efficient than those by tartaric acid or malic acid (extraction yield 30% and 80% higher, respectively).