Optimization of processing parameters for the improved production of surfactin from B. Subtilis using a statistical approach and demonstration of its imminent potential in cosmetic applications

Bacillus lipopeptides are promising biosurfactants that find applications in various sectors like biotechnological, cosmetics and biopharma due to their outstanding functionality like high specificity, low toxicity, and high surface activity. Among the different Bacillus species, Bacillus subtilis is well known for producing a biosurfactant surfactin. The objective of the work was to optimize the process parameters such as temperature, working volume and agitation speed that critically influence the surfactin production in batch cultivation systems using shake-flasks. Optimization of surfactin production was carried out using response surface methodology (RSM). To evaluate the significance of the processing parameters and to locate the actual optimal condition (which significantly affected the lipopeptide production) the Central Composite Design (CCD) method was used. The optimal conditions were found to be a culture volume of 250 mL (in a 500 mL conical flask), a temperature of 37°C and an agitation speed of 250 rpm with the maximum surfactin concentration of 1.49 g/L. Results of RSM showed that the predicted response could be closely correlated with the experimentally obtained production. A kinetics study on surfactin production, substrate consumption and biomass production at optimal conditions was carried out. Overall, this study provided an efficient method for optimizing the process parameters by reducing the production cost and enhancing the production of surfactin. Partially purified surfactin based cosmetic nanoemulsion remained stable for over 100 days maintained and found to have hydrodynamic diameter of 170 and 173.9 nm and PDI of 0.178 and 0.170 on 0th and 100th day, respectively, at 28 °C. On the successful formulation of stable nanoemulsion, plant-sourced thickener, xanthan gum, was incorporated in formulating thickened cosmetic emulsion. Thickened nanoemulsion exhibited pseudoplastic behaviour and has a hydrodynamic diameter of 173.2 nm and PDI of 0.177, proving that the introduction of xanthan gum did not affect the stability.