Sustainable paramylon production from food waste by Euglena gracilis using a waste-based cell immobilisation technique

Microalga represents a promising platform for numerous valuable bioproducts, but the production cost and efficiency remain major challenges for the industrial implementation. In this study, the production of paramylon (polysaccharides) from microalga Euglena gracilis using food waste hydrolysate and cell immobilisation cultivation was assessed. Synthetic medium supplemented with food waste hydrolysate proved to be a feasible option and achieved the paramylon productivity of 1.46 g/L/day in the heterotrophic (HT) cultivation. In addition, waste-based supporting materials were investigated for cell immobilisation cultivation, and waste sponge demonstrating good cell viability and paramylon productivity with maximum of 2.22 g/L/day was achieved using the synthetic medium in HT condition. However, sugarcane bagasse was not suitable for E. gracilis immobilisation as it induced serious cell lysis and oxidative stress under heterotrophic cultivation. The subsequent utilisation of the hydrolysate-based medium coupled with waste-based cell immobilisation cultivation resulted in the paramylon productivity of 1.77 g/L/day, demonstrating a promising fermentation strategy for sustainable and efficient paramylon production. This study serves as a noteworthy example of producing microalgal metabolites from the food waste hydrolysate using waste-based cell immobilisation technique. Overall, our findings provide valuable insights into green and sustainable production of microalgal biorefineries, and contributes to the advancement of the circular bioeconomy.