Supramolecular-solvent based extraction of hydroxytyrosol from brines of the processing of table olives

Abstract

The recovery of bioactive compounds from agri-food waste is a growing sector and in line with the principles of green chemistry. In the last two decades, the development of processes for the extraction and purification of bioactive compounds that are cheaper, faster, simple, efficient, safe and ecological has been investigated. In this study, we develop for the first time a simple liquid–liquid extraction method of hydroxytyrosol from brines of the processing of table olives, an abundant and underutilized waste of the olive industry as alternative to nanofiltration and sorption onto resins. Brines contain a high concentration of phenolic compounds with beneficial health properties, the major compound being hydroxytyrosol. For the extraction of hydroxytyrosol from brines, green supramolecular solvents (SUPRASs) made up of 1,2-hexanediol and water and induced by salts (Na2SO4 and sodium citrate) were used, all innocuous and authorized ingredients for use in the cosmetic industry. The extraction process of hydroxytyrosol from brines was optimized (in terms of the amount of 1,2-hexanediol and salt for the synthesis of SUPRAS). The highest concentrations of hydroxytyrosol in the SUPRAS extracts (~0.5–0.9% w/w) were obtained with 4.8% v/v of 1,2-hexanediol and 1 M of Na2SO4 for synthesis (equivalent to a SUPRAS:sample ratio of 1:20 v/v in the extraction process). The final extracts were further analyzed by liquid chromatography and high resolution mass spectrometry to identify other compounds of interest.