Batch and fed-batch fermentation of optically pure D (-) lactic acid from Kodo millet (Paspalum scrobiculatum) bran residue hydrolysate: growth and inhibition kinetic modeling

Abstract

A low-cost Kodo millet bran residue was utilized as feedstock for the production of D (−) lactic acid (DLA) using Lactobacillus delbrueckii NBRC3202 under anaerobic condition. Data culled from a series of batch fermentation processes with different initial Kodo millet bran residue hydrolysate (KMBRH) and DLA concentrations were used for kinetic model development. Both simulated and experimental data were in good agreement for cell growth, KMBRH utilization, and DLA formation. The values of kinetic constants specific growth rate, (μ_m = 0.17 h⁻¹); growth (α_P = 0.96 g.g⁻¹) and non-growth (β_P = 1.19 g.g⁻¹.h⁻¹) associated constant for DLA production and the maximum specific KMBRH utilization rate, (q_{G, max} = 1.18 g.g⁻¹.h⁻¹) were in good agreement with the literature reports. Kinetic analysis elucidated that L. delbrueckii growth was predominantly influenced by KMBRH limitation and highly sensitive to DLA inhibition. Fed-batch fermentation studies demonstrated the existence of substrate and product inhibition paving the scope for process intensification.

Keywords:

• D (−) lactic acid
• kinetic modeling
• substrate inhibition
• product inhibition
• millet bran
• Luedeking-Piret equation

Acknowledgements

We are thankful to Mr. Sudhan, AR Radhakrishnan and Co, Theni district, Tamil Nadu, India for providing us millet bran samples for carrying out the project. Authors thank Department of Biotechnology, Kamaraj College of Engineering and Technology Management Board for their valuable support in successfully doing the project. Authors specially thank Department of Bioscience and Bioengineering and Department of Chemical Engineering, IIT Guwahati for providing us the lab facility for successful completion of this study. Authors also acknowledge the encouragement and support rendered by Mr. Srikanth, Mr. Satya Sai Pavan and Mr. Ganesh.

Disclosure statement

The authors declare that they have no conflict of interest.