Toxic effects of extractants and carriers of specific microorganisms must be taken into account before using them with hybrid fermentation processes that are combined with liquid membranes or liquid-liquid extraction. In the current research three extractants (trioctylamine, tri-iso-octylamine and Aliquat 336), three diluents (dodecane, dodecanol, and oleyl alcohol) and two mixtures (extractant/diluent) were tested for molecular toxicity on the bacteria Lactobacillus casei ATCC 393 as potential components of a liquid membrane or a liquid-liquid extraction process for lactic acid removal in an intensified fermentation process. Glucose consumption, lactic acid production, and cell growth were used as toxicity indicators. Physical properties of extractants and diluents were related to the molecular toxicity on the microorganism. These results show that mixtures of tri-iso-octylamine/dodecane and trioctylamine/dodecane at a proportion of 1:9 v/v have great potential to be used in liquid membranes or liquid-liquid extraction processes on hybrid fermentations with Lactobacillus caseiATCC 393.