Evaluation of the Fermentation Potential of Pulp Mill Residue to Produce d(−)-Lactic Acid by Separate Hydrolysis and Fermentation Using Lactobacillus coryniformis subsp. torquens
Lactic acid is widely used in chemical, pharmaceutical, cosmetic, and food industries, besides it is the building block to produce polylactic acid, which is a sustainable alternative biopolymer to synthetic plastic due to its biodegradability. Aiming at producing an optically pure isomer, the present work evaluated the potential of pulp mill residue as feedstock to produce d(−)-lactic acid by a strain of the bacterium Lactobacillus coryniformis subsp. torquens using separate hydrolysis and fermentation process. Enzymatic hydrolysis, optimized through response surface methodology for 1 g:4 mL solid/liquid ratio and 24.8 FPU/gcellulose enzyme loading, resulted in 140 g L−1 total reducing sugar and 110 g L−1 glucose after 48 h, leading to 61 % of efficiency. In instrumented bioreactor, 57 g L−1 of d(−)-lactic acid was achieved in 20 h of fermentation, while only 0.5 g L−1 of l(+)-lactic acid was generated. Furthermore, product yield of 0.97 g/g and volumetric productivity of 2.8 g L−1 h−1 were obtained.
KeywordsPulp mill residue Separate hydrolysis and fermentation Enzymatic hydrolysis d(−)-lactic acid Lactobacillus coryniformis subsp. torquens
The authors would like to thank the colleagues of LADEBIO/EQ/UFRJ for all technical support during the experiments and the AGIR/UFF for PIBITI scholarship.
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