One-step extraction and hydrolysis of crocin into crocetin by recyclable deep eutectic solvents

Abstract

Crocetin, an aglycone derived from crocin, is synthesized in biological systems through the hydrolysis of crocin as a bioactive metabolite, which is closely associated with its pharmacodynamic effects. This research demonstrates, for the first time, that deep eutectic solvents (DES) could not only exhibit excellent solubilizing properties for crocin-based compounds, but also offer a protic medium capable of catalyzing the cleavage of glycosides to yield crocetin. A series of bifunctional and recyclable DES was proposed and characterized using attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR), differential scanning calorimeter (DSC), and cytotoxicity analysis. The benzyltriethylammonium chloride-oxalic acid dihydrate (TEBAC-OA, 1:1.5, mol/mol) was tailor-made for the simultaneous extraction and conversion process with a solid-to-liquid ratio of 1:20 and heating at 80 °C for 30 min. The yield of crocetin could reach 8.485 mg/g. Following the processing, DES and crocetin were successfully recovered separately, resulting in a 94% recovery rate for crocetin. The used DES was then utilized in the subsequent processing step, maintaining a production efficiency of 95.8%. Additionally, the cytotoxicity assessment revealed that the final used eutectic systems exhibited lower cytotoxicity compared to other commonly used solvents. The hydrogen bonding energy between DES and crocin, as well as the acidity of DES, were found to have a strong correlation with the yield of crocetin. Consequently, this study has successfully developed a sustainable, efficient, and simple technique for the one-step production of crocetin from gardenia fruit.