Background: Hyaluronic acid (HA) is an important mucopolysaccharide of higher molecular weight range and holds sheer economic interest. Its applications are widely acknowledged in rheumatoid arthritis treatment, tissue engineering, and cosmetics industries. This present investigation aims for the fed-batch production of high molecular weight range HA by application of real-time metabolic heat measurements.
Results: Fed-batch strategies based on Feedforward (FF) and Feedback (FB) control was devised to improve the Molecular Weight (MW) of HA production by S. zooepidemicus. Metabolic heat measurements (Fermentation calorimetry) were modeled to decipher real-time specific growth rate, µest was looped to the PID circuit, envisaged to control µSP to their desired setpoint values 0.05 h-1, 0.1 h-1 and 0.15 h-1 respectively. The developed FB strategy established a robust control on maintaining the specific growth rate (µ) close to the µSP value with a minimal tracking error. Exponential feed rate carried out with a lowest µSP of 0.05 h-1 improved the MW of HA significantly to 2.98 MDa and 2.94 MDa for the FF and FB based control strategies respectively. An optimal HA titer of 4.73 g/L was achieved in a FF control strategy at µSP = 0.15 h-1. Biomass and Lactic acid (LA) concentrations were found to be concomitant with the increase in µSP from 0.05 h-1 to 0.15 h-1. Superior control of µ at low µSP value was observed to influence positively the HA polymerization attributing to improved MW and desired Polydispersity Index (PDI) of HA.
Conclusions: This present investigation attempts to address the metabolic bottleneck in synthesis of high MW HA by S. zooepidemicus and illustrates the application of calorimetric fed-batch control of µ at a narrower range. PID control offers advantage over conventional fed-batch method to synthesize HA at an improved MW. Calorimetric signal based µ control by PID negates adverse effects due to the secretion of other metabolites albeit maintaining homeostasis.