Summary:
Opuntia ficus-indica is a domesticated species of cactus and constitutes a plant of commercial importance in most arid and semi-arid areas of the world. In Greece it is found mainly as a native plant in southern areas and islands, where the climate is mostly xerothermic. It is used mainly for its fruits and cladodes (particularly in Mexico), while its seeds constituted an untapped plant resource/tissue until very recently. Today the seeds are utilized for the extraction of rich oil, which is used in the cosmetics industry due to the seeds’ high content of polyunsaturated fatty acids (PUFAs). The seeds of this plant offer a high potential for exploitation, since research has proven that they are rich in antioxidants (due to phenolic compounds).
In the present research ultra sound assisted extraction (USAE) was conducted in an initial sample of 550g of seeds of a Greek variety, followed by quality control with the use of chromatographic methods (TLC and HPLC) both of the hydroalcoholic solution (EtOH:H2O) and the hexane extraction. Following that, enrichment (sugar elimination) of the hydroalcoholic solution was conducted with the use of resin XAD-4, as well as fractionation with the use of Fast Centrifugal Partition Chromatography (FCPC). Both the extracts and fractions were tested for antioxidant, antimicrobial and bleaching activity with the use of the DPPH method, Kirby-Bauer and tyrosinase enzyme inhibition. The research then focused on the isolation of main secondary metabolites of the hydroalcoholic solution, which appeared with the use of thin-layer preparative high-performance liquid chromatography (preparative- HPTLC). The identification of molecules was achieved with the use of NMR 1 and 2D spectroscopy (1H-NMR, HSQC-DEPT, HMBCκαι COSY). Finally, the metabolites were tested for their antioxidant and bleaching activity and their initial bio-assay guided isolation was confirmed.
In total, 8 metabolites were isolated: 4 dihydrobenzo[b]furan neolignans, 2 ferulic acid glucosides, 1 sinapic acid glucoside and 1 coniferyol glucoside. Finally, 4 metabolites were isolated for the first time from the seeds of Opuntia ficus-indica, while 2 constitute new natural products.
Keywords:
seeds, Opuntia ficus-indica, isolation, identification, molecules
