Statistical optimisation and analysis of biomass and exopolysaccharide production by Lacticaseibacillus rhamnosus LRH30.

Exopolysaccharides (EPS) produced by lactic acid bacteria with immunomodulatory potential are promising natural food additives. This study employs small-scale, 250 mL bioreactors combined with a central composite design to optimise two important bioprocess parameters, namely temperature and airflow, to achieve high yields of biomass and EPS from Lacticaseibacillus rhamnosus LRH30 (L. rhamnosus LRH30). A quadratic model was determined to be the best fit for the production of both products. The optimum critical process parameters for maximised biomass were identified to be 37.01 °C with an airflow of 0.12 vvm, while optimum criteria was 20.1 °C with an airflow of 0.18 vvm for maximum EPS production. Under these optimized conditions, small-scale batch experiments yielded a biomass concentration of 10.1 g/L and an EPS yield of 520.2 mg/L. In comparison, scale-up experiments in 2L reactors resulted in a biomass concentration of 8.54 g/L (a reduction of 18%) and an EPS yield of 654.6 mg/L (an increase of 26%). The produced EPS was purified and characterised through Fourier transform infrared spectroscopy and showed characteristic peaks associated with polysaccharides. The immunomodulatory potential of the L. rhamnosus LRH30 cells and EPS was evaluated through cytokine and chemokine secretion in a J774A.1 murine macrophage, resulting in a predominantly anti-inflammatory effect of L. rhamnosus LRH30 and EPS.