Production of single cell protein from ryegrass residual liquid fraction in a green biorefinery process

The global food system's contribution to climate change, combined with the rising demand for protein, highlights the need for sustainable protein sources. Microbial biomass represents a promising solution, with residual liquid fraction from green biorefineries offering a suitable carbohydrate-rich substrate. In this study single cell protein production was evaluated using ryegrass residual juice as substrate. Three yeast species – Kluyveromyces marxianus, Yarrowia lipolytica, and Cyberlindnera jadinii – were first screened in shake flasks to identify the most suitable candidate for further investigation. Batch fermentations with C. jadinii were conducted in bioreactors, with and without nitrogen supplementation. Nitrogen addition improved both biomass concentration and crude protein content, reaching 19.9 g/L of dry cell mass and 57.4 % (w/w) protein content after 48 h. Yields were 0.67 g of dry cell mass and 0.39 g of protein per gram of total sugar consumed. These findings demonstrate the potential of ryegrass residual juice as substrate for single cell protein production and highlight the benefits of nitrogen supplementation in optimizing fermentation performance.