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Effect of thermo-chemical pretreatment on the saccharification and enzymatic digestibility of olive mill stones and their bioconversion towards alcohols

  • Waste and Biomass Management & Valorization
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Abstract

The present study investigated the effect of thermo-chemical pretreatment on the enhancement of enzymatic digestibility of olive mill stones (OMS), as well as its possible valorisation via bioconversion of the generated free sugars to alcohols. Specifically, the influence of parameters such as reaction time, temperature, type and concentration of dilute acids and/or bases, was assessed during the thermo-chemical pretreatment. The hydrolysates and the solids remaining after pretreatment, as well as the whole pretreated slurries, were further evaluated as potential substrates for the simultaneous production of ethanol and xylitol via fermentation with the yeast Pachysolen tannophilus. The digestibility and overall saccharification of OMS were considerably enhanced in all cases, with the maximum enzymatic digestibility observed for dilute sodium hydroxide (almost 4-fold) which also yielded the highest total saccharification yield (91% of the total OMS carbohydrates). Ethanol and xylitol yields from the untreated OMS were 28 g/kg OMS and 25 g/kg OMS, respectively, and were both significantly enhanced by pretreatment. The highest ethanol yield was 79 g/kg OMS and was achieved by the alkali pretreatment and separate fermentation of hydrolysates and solids, whereas the highest xylitol yield was 49 g/kg OMS and was obtained by pretreatment with sulphuric acid and separate fermentation of hydrolysates and solids.

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Funding

We acknowledge financial support of this work by the project “Research infrastructure for Waste Valorization and Sustainable Management of Resources, INVALOR” (MIS 5002495) which is implemented under the “Action for the Strategic Development on the Research and Technological Sector”, funded by the Operational Programme “Competitiveness, Entrepreneurship and Innovation” (NSRF 2014-2020) and co-financed by Greece and the European Union (European Regional Development Fund).

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Correspondence to Ioanna Ntaikou.

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Responsible editor: Ta Yeong Wu

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Ntaikou, I., Siankevich, S. & Lyberatos, G. Effect of thermo-chemical pretreatment on the saccharification and enzymatic digestibility of olive mill stones and their bioconversion towards alcohols. Environ Sci Pollut Res 28, 24570–24579 (2021). https://doi.org/10.1007/s11356-020-09625-z

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  • DOI: https://doi.org/10.1007/s11356-020-09625-z

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