A biorefinery approach to obtain antioxidants, lignin and sugars from exhausted olive pomace

Abstract

Exhausted olive pomace (EOP) is the main residue of the pomace olive oil extracting industry. In this work, EOP was fractionated into valuable components for valorisation: an aqueous extract rich in hydroxytyrosol and mannitol, lignins with antioxidant properties and fermentable sugars. EOP was first subjected to water extraction at 85 °C for 90 min. Several pretreatments based on liquid hot water and organosolv with 50% or 60% ethanol (catalysed and uncatalysed with 1% sulfuric acid) were then evaluated in terms of delignification ability and efficiency for enzymatic hydrolysis of the pretreated solids. Once the best conditions had been selected (50 % ethanol-1% sulfuric acid at 130 °C for 60 min), an organosolv lignin (OL) with antioxidant properties was obtained through acid precipitation of the pretreatment liquor. This was compared to the enzymatic hydrolysis lignin obtained in the subsequent step and to the lignins purified by acid hydrolysis. OL showed a higher total phenolic content and antioxidant activity than the rest of the lignin samples. Chemical differences were also observed that could explain the results.