Processing of extracted olive oil pomace residue by hydrothermal or dilute acid pretreatment and enzymatic hydrolysis in a biorefinery context

Abstract

In this work, a residue from olive oil industry, i.e., extracted dry olive pomace (EOP), which is generated in pomace oil extracting industries after removing residual oil from dry pomace, is studied for valorization into fermentable sugars and other added-value compounds by hydrothermal or dilute acid pretreatment, followed by enzymatic hydrolysis. An EOP sample is processed by a first step of water extraction during 30 min at 100ºC in autoclave, followed by Liquid Hot Water (LHW) pretreatment at 170 and 190ºC, or dilute acid (DA) pretreatment, at the same temperatures in sulfuric acid [1% and 2% (w/v)] media. The extracted and pretreated EOP is then submitted to enzymatic hydrolysis (EH) tests at laboratory scale using commercial enzymes to estimate sugar production yield. From these results of EH tests and the analysis of intermediate solid and liquid EOP derived fractions, the yield of sugar production from water-extracted and pretreated EOP was estimated and a mass balance for glucose and xylose along the whole process calculated. Results show that the water-extraction step allows concentrating main components for the subsequent step of LHW/DA, and extracting other valuable compounds as mannitol and phenolic compounds that can contribute significantly to EOP valorization. LWH and DA pretreatment are found to be effective methods to fractionate EOP biomass and facilitate sugar release by EH, although DA performs comparatively better, providing the maximum overall process yield considering both glucose and xylose sugars (85 and 62% of sugar content in raw EOP) at 170ºC and 2% acid.