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ABSTRACT Lactic Acid (LA) is a versatile compound with extensive industrial usage. Lactic Acid Bacteria (LAB) are renowned for their capacity to ferment carbohydrates to LA. In the biodiesel industry, bioconversion of residual glycerol to monomers of biopolymers, such as LA, is an alternative for usage of this waste as raw material to produce a high value added biotechnological compound. This research evaluates LA production through fermentation processes using a Lactobacillus sp. native strain and raw glycerol from the biodiesel industry. Native strain was isolated from the processing of dairy, fruit, and vegetable products and through cultures in Man, Rogosa & Sharpe agar (MRS). After an adaptation phase, the fermentative capability of the strain was evaluated through chemical quantification of metabolites using Nuclear Magnetic Resonance (¹H-NMR); fermentative potential was compared with a Lactobacillus sp. reference strain (ATCC 7469). The native strain Lactobacillus sp. CYP4 showed a higher bioconversion potential (LA concentration: 39.41 mM, conversion percentage: 39.27%, at 24 h, volumetric productivity: 1.28 g.L-1.h-1, yield: 0.71 g·g-1) from raw glycerol, when compared to the reference strain.

This study show the capability of Lactobacillus rhamnosus ATCC 7469 to produce lactic acid using crude glycerol from biodiesel production as carbon source; in addition, a kinetic model that describes the behaviour of the fermentation process using USP glycerol as substrate was proposed and developed. The strain was adapted to the new carbon source by doing successive cultures, the substrate conversion was up to 94.5% after 24 hours of fermentation using crude glycerol as under initial conditions of substrate concentration (crude glycerol) and pH of 8 g/L and 6.5, respectively. Then, the influence of initial pH (pHo) and concentration of substrate (So) were evaluated by fermentation tests of USP glycerol. The optimal value of volumetric lactic acid productivity (Qv) achieved from this study was 0.087 g·L-1·h-1 for initial pHo = 6.5 and initial substrate concentration So = 6 g/L. Lastly, the kinetics parameters of an unstructured and not segregated model (Aiba type equation for growth rate expression), were adjusted with an average fit degree of 88% for all the initial conditions, using USP glycerol. In addition, the kinetic parameters are laid out as function of initial pH and substrate concentration.