Preliminary Study On Surface Properties And Bioactivities Of Two Kinds Of Sophorolipids

Biosurfactants are a large class of surface-active compounds produced by microorganisms. As secondary metabolites, biosurfactants can be synthesized by fermentation using renewable resources. In addition to superior physical and chemical properties similar to chemical surfactants, biosurfactants also have low toxicity, environmental compatibility and biodegradability. Sophorolipids are amphiphilic molecules which have sophorose and hydroxy fatty acids as their hydrophilic and hydrophobic groups. They are probably one of the most promising biosurfactants because they can be produced by non pathogenic yeast strains with high production yields and substrate conversion rate. Due to their good surface properties and bioactivities like antibacterial, antiviral, antitumor, antioxidant activity as well as other biological functions, sophorolipids can be widely used in petroleum exploration, environmental engineering, food, medicine, cosmetics and detergent industries.Sophorolipids produced by microbial fermentation are composed of fractions with different structures. The main differences include whether the fatty acid molecules can form lactone and acetylation level of sophorose molecules. These structural differences give sophorolipids different physical and chemical properties and biological activities. Different strains and fermentation conditions will affect the proportion of structurally different sophorolipids in the fermentation products, and the substrate had the greatest impact. Surface characteristics, antibacterial activities, anti-tumor and antioxidant activities of two sophorolipids were analyzed in this study. Two sophorolipids were produced by Candida bombicola using glucose, oleic acid as cosubstrate (SL-G) and soybean oil as sole substrate (SL-S) respectively, the results as follows:1) Surface tension of two sophorolipids with different concentrations was determined, the minimum surface tension was obtained according to concentration curve of surface tension, the values of SL-G and SL-S were 38 and 40 mN/m respectively, critical micelle concentrations were 60 and 70 mg/L. Sophorolipids preserve their surface lowering properties despite high salt concentrations and are in addition active across a wide temperature range. They were unstable under strong acid and alkaline conditions. Emulsifying activity of two sophorolipids was analyzed and emulsification rates were higher than 80% in the soybean oil, sesame oil and paraffin.2) Inhibitory zone diameters of two sophorolipids were determined by filter paper method and antibacterial activities of them were analyzed. Both of them had good inhibitiory effects on bacteria, while no effects on plant pathogens. At high concentration, SL-S had better antibacterial effect compared with SL-G, but weaker at low concentration. SL-G had smaller MIC than SL-S, the values of them were 3.125 mg/ml and 50 mg/ml respectively. The antibacterial activities of two sophorolipids were affected by strong alkali but stable at high temperature. Ultrastructure destruction of Staphylococcus aureus due to sophorolipids was observed under scanning and transmission electron microscopy. Deformation, obvious plasmolysis, cytoplasmic condensation, and cavity were appeared after cultured with sophorolipid for 8h, and most cells were severely damaged.3) In vitro antitumor activities of two sophorolipids to cervical cancer Hela cells and gastric cancer 823 cells were analyzed by MTT method. Both of them had good inhibitory effects, and the effect for 823 cells was more obvious than Hela cells. Inhibitory activities of SL-S for both kinds of cancer cells were higher than SL-G.4) Antioxidant activities in vitro of two sophorolipids were determined by DPPH radical scavenging experiment, SL-S had better antioxidant activity than SL-G.In summary, it was revealed in this study that sophorolipids are a class of biosurfactant with good surface properties and bioactivities, which may replace chemical surfactants. It was verified that different surface properties and bioactivities were due to the structural differences of sophorolipids produced by different substance fermentation,too. This study provides a certain basis for development of sophorolipid as new bio-surfactants, antibacterial agents, anti-cancer drugs and anti-oxidants. It also offers some clues for analyzing the specific molecular structures of sophorolipids that determine their bioactivities.