A holistic engineering approach for utilization of olive pomace

•Olive pomace was processed with SC-CO2, followed with hydrolysis of the raffinate phase.•Optimum conditions were elicited as 68 °C, 280 bar and 20 g/min flow yielding 4.8% oil.•The yield was increased to 13.8% by decreasing the particle size from 2000 to 850–500 μm.•SC-CO2 de-oiled fraction yielded 12.30 and 12.72 g/l reducing sugar by acid and enzymatic hydrolyses.

Olive pomace is a by-product of olive oil production and an important biomass for the Mediterranean countries. The aim of this study was to optimize the oil extraction from olive pomace by supercritical CO2 and utilize the remaining biomass by hydrolysis. A Box–Behnken statistical design was used to evaluate the effect of temperature (30–80 °C), pressure (120–300 bar) and CO2 flow rate (10–20 g/min) for 60 min. The most effective variable was pressure (p < 0.005) and optimum extraction conditions were elicited as 68 °C, 280 bar and 20 g/min flow rate yielding 4.8% of oil. Additionally, the effect of particle size was investigated on extraction efficiency. Indeed, the oil yield was increased to 13.8% by decreasing the particle size from 2000 to 850–500 μm. For utilization of remaining biomass, both supercritical CO2 (SC-CO2) and hexane de-oiled pomaces were subjected to acid and enzymatic hydrolyses. Hydrolyses with 2% of sulfuric acid for 90 min yielded 12.30 and 12.65 g/l reducing sugar from SC-CO2 and hexane treated biomasses, whereas the highest reducing sugar concentrations achieved with enzymatic hydrolysis with a substrate amount of 6 g, 20–27% Cellic CTec2/Novozyme 188 for 24 h were 12.72 g/l and 10.13 g/l, respectively. A holistic engineering approach is proposed where supercritical CO2 can be used as a main process to extract remaining oil in olive pomace and as a pretreatment loosen the structure in order to obtain liquor which can be converted to a biofuel.

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