Assessing multiple bioprocess modes for lactic acid production by Lactiplantibacillus plantarum ATCC 8014 using lactose as a substrate

Abstract

Lactose as a primary carbon source for fermentation is not as thoroughly investigated as glucose, despite certain advantages such as potential sourcing from high volume dairy side-streams. We investigated whether lactose could be a feasible feed source for various lactic acid bacteria (LABs) to produce lactic acid (LA), which is a precursor for the synthesis of the bioplastic polylactic acid. In 1 Litre stirred tank bioreactors under microaerophilic batch growth conditions Lactiplantibacillus plantarum ATCC 8014 had the highest LA titre (40 g L⁻¹) and productivity (0.83 g L⁻¹ h⁻¹) compared to other LABs tested. When air was supplied to the bioreactor at 10% dissolved oxygen, L. plantarum ATCC 8014 fully consumed the lactose supplied to produce 40 g L⁻¹ LA and increased the LA volumetric productivity to 1.51 g L⁻¹ h⁻¹ in 28 hours. Fed-batch fermentations with L. plantarum ATCC 8014 achieved the highest LA titre (69.05 g L⁻¹) but productivity was reduced (1.28 g L⁻¹ h⁻¹) compared to the best batch cultures. Under continuous culture conditions (D = 0.1 h⁻¹) L. plantarum ATCC 8014 had the highest LA yield (0.88 g g⁻¹) from lactose but the titre was low (4 to 6 g L⁻¹) and productivity was not stable.