Feasibility of converting lactic acid to ethanol in food waste fermentation by immobilized lactate oxidase

• Residue lactic acid in food waste could be converted to pyruvic acid.
• Calcium alginate immobilized the lactate oxidase with high pH and thermal stability.
• Immobilized enzyme could convert 70% lactic acid to pyruvic acid.
• Ethanol yield could be increased by 20% with lactate oxidase added.

Adoption of lactic acid bacteria (LAB) into ethanol fermentation from food waste can replace the sterilization process. However, LAB inoculation will convert part of the substrate into lactic acid (LA), not ethanol. This study adopted lactate oxidase to convert the produced LA to pyruvate, and then ethanol fermentation was carried out. The immobilization enzyme was utilized, and corresponding optimum conditions were determined. Results showed that calcium alginate could successfully immobilize the enzyme and improve pH and thermal stability. The optimum pH and temperature were 6.2 and 55 °C, respectively. The utilization of immobilized enzyme with catalytic time of 5 h could convert 70% LA to pyruvate, and the addition of enzyme increased the ethanol yield by 20% more than that of the control. The process could be applied in food waste storage and can help in reducing carbon source consumption.