Identification and characterization of bioemulsifier-producing yeasts isolated from effluents of a dairy industry

New bioemulsifier-producing yeasts were isolated from the biological wastewater treatment plant of a dairy industry. Of the 31 bioemulsifier-producing strains, 12 showed emulsifying activity after 2 months of incubation, with E24 values ranging from 7% to 78%. However, only Trichosporon loubieri CLV20, Geotrichum sp. CLOA40, and T. montevideense CLOA70 exhibited high emulsion-stabilizing capacity, with E24 values of 78%, 67%, and 66%, respectively. These isolates were shown to induce a strong emulsion stabilizing activity rather than the reduction of the interfacial tension. These strains exhibited similar growth rates in the exponential growth phase, with a clear acceleration after 24 h and stabilization of the activity after 144 h. Emulsification and stability properties of the bioemulsifiers were compared to those of commercial surfactants after the addition of NaCl and exposure to temperature of 100 °C. The compounds produced by the isolates appeared to be lipid–polysaccharide complexes. Gas chromatograph analysis of the lipidic fraction of the bioemulsifiers from CLV20, CLOA40, and CLOA70 shows the prevalence of (9Z,12Z)-octadeca-9,12-dienoic acid, in concentrations of 42.8%, 25.9%, and 49.8%, respectively. The carbohydrate composition, as determined by GC–MS of their alditol acetate derivatives, showed a predominance of mannose, galactose, xylose and arabinose.