Rapid screening of solvents and carrier compounds for lactic acid recovery by emulsion liquid extraction and toxicity on Lactobacillus casei (ATCC 11443)

This paper describes a rapid method to identify the best solvent and carrier compound combinations with the highest extraction capability and the lowest microbial toxicity characteristics for product recovery from microbial fermentation. The extraction system has an aqueous phase, and an emulsion phase, which was a blend of sodium carbonate and organic phase [91% (v/v) organic solvent, 5% (v/v or wt/v) carrier compound, and 4% (v/v) surfactant Span 80]. Alamine 336, or tri-n-octylamine in n-heptane; Alamine 336, Alamine 304, or tributyl phosphate in hexane; and Alamine 304 or tributyl phosphate in iso-octane; Alamine 304 or Amberlite in xylene demonstrated high lactic acid extraction. For determination of bacterial toxicity of selected solvent and carrier compounds, Lactobacillus casei subsp. rhamnosus (ATCC 11443) was grown in LAF medium containing one of the selected organic solvent, carrier compound, and Span 80 in 250 ml flask at 37 degrees C and 125 rpm. Samples were collected regularly during 48 hour incubation, and measured for changes in cell density by absorbance at 620 nm, cell count using a fluorescent dye with flow cytometry, and lactic acid, and glucose concentrations by HPLC. Hexadecane: tributyl phosphate, n-dodecane:tri-n-octylamine, and kerosene: tri-n-octylphosphine oxide demonstrated the least microbial toxicity among the tested blends with excess solvent media. Whereas, hexanes: Alamine 304 and xylenes: Alamine 304 were nontoxic in solvent saturated media.