Recovery of polyphenols from olive mill wastewater using drowning-out crystallization based separation process

• Novel method for the recovery of polyphenols from OMW has been developed.
• Drowning-out separation process was adopted for polyphenol recovery from OMW.
• Highly-concentrated polyphenols were achieved in the outcome (up to 75% (w/w)).
• Up to (510 mg/g) of the recovered polyphenols content was hydroxytyrosol.

Olive oil extraction generates a large amount of olive mill wastewater (OMW) (10 million ton/year), requiring specific management to minimize its potential negative impact on the environment. However, OMW is a rich source of polyphenols having a wide range of bioactivities. For that reason, the selective recovery of polyphenols from OMW provides the double opportunity to obtain bioactive compounds and to reduce its phytotoxicity.The present study relates to a highly efficient and novel method, using green technology, for obtaining a natural bioactive concentrate rich in polyphenols from OMW. The clean technology integrates centrifugation, batch evaporation and drowning-out crystallization-based separation process, for the separation of polyphenols from the different components present in OMW, based on the solubility behavior changing after addition of ethanol, accepted as food grade. Further, batch evaporation was applied for the regeneration of ethanol for sustainable process. Consequently, the proposed method provides a highly-concentrated polyphenols isolate (up to 75% (w/w)), with up to (510 mg/g) of the polyphenols content being hydroxytyrosol. The recovered polyphenols can be of interest for the food industry, cosmetic industry, or pharmaceutical industry.Industrial relevanceDrowning-out separation process by ethanol was found useful to achieve the main target for the recovery of polyphenols from OMW. Polyphenol concentration increased considerably by the proposed method based on the solubility behavior changing after addition of ethanol, a food grade solvent. Furthermore, batch evaporation was carried out for the regeneration of ethanol, which can be reused in the process. Polyphenols concentrate (up to 75% (w/w)) developed in this study have the potential for application in food industry (e.g. to develop a premium olive oil containing 1000 ppm of polyphenols, or developing e.g. grape juice with enhanced polyphenols content), or into cosmetics (e.g. developing a lotion/hand cream with high antioxidant content), or into pharmaceutics (e.g. developing capsules high polyphenols content; which could also be considered as food supplement).

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