Sustainable Production of Lactic Acid Using Lolium perenne as Feedstock—A Comparative Study of Fermentation at Bench- and Reactor-Scale, and Ensiling

Perennial ryegrass (Lolium perenne) is an underutilized lignocellulosic biomass that has several benefits such as high availability, renewability, and biomass yield. The grass press-juice obtained from the mechanical pretreatment can be used for the bio-based production of chemicals. Lactic acid is a platform chemical that has attracted consideration due to the broad area of applications. For this reason, a more sustainable production of lactic acid is expected to increase. In this work, lactic acid was produced using complex medium at bench- and reactor scale, and the results were compared to those obtained using an optimized press-juice medium. Bench-scale fermentations were carried out in a pH-control system and lactic acid production reached about 22 g/L in com-plex medium, and 26.61 ± 1.2 g/L in press-juice medium. In bioreactor, the production yield was 0.91 ± 0.07 g/g, corresponding to 1.4-fold increase respect to the complex medium with fructose. As comparison to the traditional ensiling process, whole grass fractions of different varieties har-vested in summer and autumn was performed. Ensiling showed variations in lactic acid yields, with a yield up to 15.2% dry mass for the late-harvested samples, surpassing typical silage yields of 6-10% dry mass.