Investigation of lactic acid production by pressurized liquid hot water from cultivated Miscanthus × giganteus

Abstract

The production of lactic acid, a polylactic acid monomer from energy crop Miscanthus × giganteus lignocellulosic biomass cultivated in Izmir was investigated. Liquid hot water (LHW) pretreatment was carried out at a temperature range of 140–200 °C, pressure 100 to 200 bar and reaction time of 15–45 min at a fixed flow rate of 2 mL/min using D-optimal experimental plan. The optimum conditions were elicited as 140 °C, 100 bar and 45 minutes, yielding the highest reducing sugar content of 77.32 mg/g, whereas 1.25 mg/mL arabinose and 1.35 mg/mL xylose as monomeric sugars. Subsequently, the enzymatic hydrolysis was applied to the solid fraction. The optimum conditions for enzymatic hydrolysis were determined as 5% (w/v) solid/liquid ratio, 20 FPU/mL enzyme loading and 72 hours, revealing the highest amount of reducing sugar as 200 mg/mL. LHW hydrolysate was used as a production medium for lactic acid manufacturing in submerged fermentation by Rhizopus oryzae. The maximum lactic acid content was found to be 6.8 g/L at 24 hours, whereas the lactic acid yield was 0.28 g/L.h. The sequential design of LHW, followed by enzymatic hydrolysis and submerged lactic acid fermentation can be utilized in industry, contributing to the bioeconomy.

Keywords:

• Miscanthus × giganteus
• biorefinery
• lactic acid
• enzymatic hydrolysis
• fermentation
• biomass

Acknowledgment

The authors specially would like to thank Prof. Hakan Geren for providing Miscanthus x giganteus biomass. Many thanks to Biorender who helped us to create graphical abstract.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions

K. Gunes: Visualization, Investigation, Writing-Original draft preparation,

S. Sargin: Writing-Original draft preparation, Visualization, Methodology, Investigation.

M. S. Celiktas: Conceptualization, Visualization, Supervision, Writing-Original draft preparation Methodology, Writing- Reviewing and Editing.

Additional information

Funding

This project was supported by Ege University, Scientific Research Projects Coordination (Project Number 17–GEE–008).