Serratia plymuthica, a Gram-negative, facultatively anaerobic bacterium previously isolated from the carrot surface, has shown strong antagonistic activity against carrot pathogens, making it a promising candidate for biological control. Its effective use in postharvest disease management relies on the development of a stable and applicable formulation. The present study focuses on the optimisation and scale-up of S. plymuthica cultivation and its formulation as a freeze-dried product intended for postharvest application on carrots.
Initially, metabolic profiling of S. plymuthica was conducted using the Biolog™ PM01-PM02 assay to assess carbon source utilisation. Based on this screening, growth performance was evaluated in shake-flask fermentations using selected carbon and nitrogen sources supplemented in LB medium. In parallel, the effects of cultivation temperature (20-37 °C) and pH (5-8) were evaluated.
The best performing conditions were transferred to controlled batch and fed batch fermentations in a 1 L bioreactor. Bacterial growth and substrate utilization were monitored using standard analytical methods. Under modified LB[Uv1.1] medium supplemented with 20 〖g L〗^(-1) glucose, the highest biomass yield reached 4.74 × 10^10 〖CFU mL〗^(-1) after 24 h.
Subsequently, the process was scaled up to a 5 L bioreactor, resulting in a final biomass concentration of 2.55 × 10^10 〖CFU mL〗^(-1) after 14 h. As a last step, the downstream process and lyophilisation successfully yielded a stable freeze-dried powder with viable cell concentrations of approximately 5 × 10^11 〖CFU g〗^(-1), suitable for application as a biopreservative agent. These findings demonstrate the scalability of the production process and provide a solid foundation for further formulation development.