Abstract
Biosurfactants are natural surfactants produced by bacteria, yeasts or fungi from different substrates, including sugars, oils, alkanes. Biosurfactants are expected to reach more than USD 2 billion by 2020, with industrial applications in microbial enhanced oil recovery (MEOR), removal of contamination by heavy metals, bioremediation, food, cosmetics, pharmaceuticals, biomedicine and nanotechnology. The considerable interest in these biobased products is related to their properties, as biodegradability, production from renewable substrates, low toxicity, biocompatibility, digestibility, diversity for chemical structure and properties, effectiveness even at extreme conditions of temperature, pH and salinity. Despite the advantages, fermentation must be cost-competitive with chemical synthesis, and many of the potential applications that have been considered for biosurfactants depend on whether they can be produced economically. Fermentation medium can represent approximately 30 % of the cost for a microbial fermentation. Nevertheless, much effort in process optimization at the engineering and biological levels has been done, and, for some applications, biosurfactants can be produced from several inexpensive waste substrates, thereby decreasing their production cost. Thus, the production of a biosurfactant by Candida guilliermondii UCP0992 was studied in a low-cost medium formulated with 2.5 % waste frying oil, 2.5 % corn steep liquor and 4.0 % molasses during 144 h at 28 °C under 200 rpm. The surface tension of the medium was reduced to below 28 mN/m. The tensoative properties of biosurfactant were investigated and its CMC (Critical Micelle Concentration) determined as 0.42 %. It had a good surface tension reduction capacity and emulsifying activity against motor oil (up to 90 %) and vegetable oils (30-55 %). It showed stability during exposure to high temperatures (up to 120 °C for 15 min), high salinity (12 % NaCl) and a wide range of pH (2-12). The crude biosurfactant did not show toxicity against the microcrustacean Artemia salina. The biosurfactant was also tested for toxicity against bacteria and filamentous fungi from seawater during 30 days. The addition of the biosurfactant to seawater stimulated the degradation of motor oil via the activity of the indigenous microorganisms. The cell-free broth (crude biosurfactant) was also effective in oil displacement (100 %) in seawater. The biosurfactant from C. guilliermondii was also effective in recovery of up to 50 % motor oil from the walls of beakers at twice its CMC. These results indicate the potential value of the biosurfactant for application in the oil industry, especially in enhanced oil recovery, tank cleaning and in bioremediation of spills at seas and soils.
