Effect of nitrogen sources and neutralizing agents on D-lactic acid production from Kodo millet bran hydrolysate: comparative study and kinetic analysis

  • Rengesh Balakrishnan
  • Subbi Rami Reddy Tadi
  • Allampalli Satya Sai Pavan
  • Senthilkumar SivaprakasamEmail author
  • Shyamkumar RajaramEmail author
Original Article


D-lactic acid (DLA) serves as a key monomer enhancing both the mechanical and thermal properties of Poly(lactic) acid films and coatings, extensively used in the food packaging industry. Economically viable production of optically pure DLA by Lactobacillus delbrueckii NBRC3202 was achieved using a low–cost carbon source, Kodo millet bran residue hydrolysate (KMBRH) and nitrogen source (casein enzyme hydrolysate (CEH) resulting in a high DLA yield of 0.99 g g−1 and KMBRH conversion to final product (95.3%). The optimum values for kinetic parameters viz., specific growth rate (0.11 h−1), yield coefficient of biomass on KMBRH (0.10 g g−1) and DLA productivity (0.45 g L−1 h−1) were achieved at 5 g L−1 of CEH dosage under controlled pH environment. A comparative study and kinetic analysis of different neutralizing agents (NaOH, NH3, CaCO3 and NaHCO3) under pH controlled environment for KMBRH based DLA production was addressed effectively through bioreactor scale experiments. Maximum cell concentration (1.29 g L−1) and DLA titer (45.08 g L−1) were observed with NH3 as a neutralizing agent. Kinetic analysis of DLA production under different neutralization agents demonstrated that the logistic derived model predicted biomass growth, KMBRH consumption and DLA production efficiently (R2 > 0.92).


D-(−)-lactic acid Millet bran Lactobacillus delbrueckii Kinetic modeling Bioreactor Neutralizing agent 

List of symbols


American society for testing and materials


Beaf extract


Brain heart infusion


Casein enzyme hydrolysate


D-(−)-lactic concentration (g L−1)


KMBRH concentration (g L−1)


Initial KMBRH concentration (g L−1)


Glucoamylase units


Kodo millet bran residue


Kodo millet bran residue hydrolysate


L-(+)-lactic acid


Maintenance coefficient (g g−1 h−1)


deMan Rogosa Sharpe


Modified MRS


Poly D-(−)-lactic acid


Poly DL lactic acid


Poly lactic acid


Poly L-(+)-lactic acid


Correlation coefficient (dimensionless)


Volumetric DLA production rate (g L−1 h−1)


Volumetric KMBRH consumption rate (g L−1 h−1)

rX (vX)

Volumetric cell growth rate (g L−1 h−1)


Supervisory control and data acquisition


Soy peptone


Time (h)


Whey protein hydrolysate


Cell concentration (g L−1)


Initial cell concentration (g L−1)


Maximum cell concentration at time (g.L−1)


Product yield on substrate consumed (g g−1)


Yeast extract


Cell yield on KMBRH consumed (g g−1)

Greek symbols


Luedeking–piret model growth associated constant for DLA (g g−1)


Luedeking–piret model non-growth associated constant for DLA (g g−1 h−1)


Specific growth rate (h−1)


Sum of squared errors (dimensionless)


Delayed time variable (Lag-time) of L. delbrueckii (h)



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.Naresh and Mr.Ganesh.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.


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Copyright information

© Association of Food Scientists & Technologists (India) 2019

Authors and Affiliations

  1. 1.Department of BiotechnologyKamaraj College of Engineering and TechnologyK.Vellakulam, Madurai DistrictIndia
  2. 2.BioPAT Laboratory, Department of Biosciences and BioengineeringIndian Institute of Technology GuwahatiGuwahatiIndia

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