Optimization of exopolysaccharide production and its physico-chemical properties from Monoraphidium contortum under batch and fed-batch conditions and evaluating its functional activities

Abstract

The evaluation of growth conditions to enhance biomass productivity, exopolysaccharide (EPS) yield, and its physicochemical properties from Monoraphidium contortum were investigated under batch and fed-batch cultivation using experimental design approaches. A Plackett-Burman design was first applied to identify crucial factors affecting algal biomass and EPS production under batch conditions. Biomass and EPS productivity, alongside physicochemical properties (intrinsic viscosity, sulfate content, uronic acids, total sugars, and protein impurities), were further optimized using a central composite design. Under optimized batch cultivation, EPS production reached 0.4 g L⁻¹ (1.14 g g⁻¹ biomass) at optimal concentrations of citric acid (0.015 g L⁻¹), Na₂CO₃ (0.23 g L⁻¹), and K₂HPO₄ (0.072 g L⁻¹). In contrast, fed-batch cultivation under periodic supplementation of citric acid (0.009 g L⁻¹) and Na₂CO₃ (0.33 g L⁻¹) at 2-day intervals in the optimized BG-11 medium, further enhanced EPS production to 0.89 g L⁻¹ (2.07 g g⁻¹ biomass). This strategy resulted in a 25.5-fold increase in EPS yield relative to the original medium. Importantly, cultivation strategy markedly influenced EPS physicochemical properties. Fed-batch growth also improved algal biomass and cellular metabolite (lipids, proteins, carbohydrates) productivity. EPS produced under optimal conditions exhibited strong antioxidant activities, with hydroxyl and superoxide radical scavenging reaching 67.29% and 78.13% at 1 mg mL⁻¹, respectively, Additionally, it showed potent anti-inflammatory activity (90.91% inhibition of protein denaturation at 10 mg mL⁻¹) and good emulsifying and foaming properties. This study highlighted the potential of cultivation strategy to enhance EPS production with tailored properties, coupled with high algal biomass and metabolite yields.