Evaluation of the Fermentation Potential of Pulp Mill Residue to Produce D(-)-Lactic Acid by Separate Hydrolysis and Fermentation Using Lactobacillus coryniformis subsp. torquens.

Abstract

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 1g:4mL solid/liquid ratio and 24.8FPU/gcellulose enzyme loading, resulted in 140gL-1 total reducing sugar and 110gL-1 glucose after 48h, leading to 61% of efficiency. In instrumented bioreactor, 57gL-1 of D(-)-lactic acid was achieved in 20h of fermentation, while only 0.5gL-1 of L(+)-lactic acid was generated. Furthermore, product yield of 0.97g/g and volumetric productivity of 2.8gL-1h-1 were obtained.