Morphology and Release Profiles of Biodegradable Microparticles Containing Rhamnolipid Biosurfactant

ABSTRACT

In an effort to expand the technology of bioremediation of hydrophobic organic compounds, microencapsulation technology was investigated as a method of biosurfactant delivery to contaminated sites. Microparticles are composed of active or inactive materials encapsulated in a polymer coating designed for controlled release of the encapsulated substance. Surface morphology and release profiles of microparticles containing rhamnolipid biosurfactant were investigated for development of a controlled release bioremediation scheme. The evaluation was conducted under laboratory conditions with 45 mg/ml concentration of biosurfactant and a representative environmental medium; using artificial salt water (35 ppt) and deionized water medium as a control. The microparticles were prepared by the water–in–oil–in–water double emulsion solvent evaporation method. The surface morphology was examined after initial preparation, at 0, 15 and 31 days incubation, using light microscopy. Light microscopic images revealed smooth, spherical microparticles that degraded over time in the media. Results indicated that microparticle degradation occurred mostly in the salt water environment, suggesting that the presence of salts (Na⁺ and Cl⁻ ions) in the water enhanced microparticle degradation. The deionized water environment achieved polymeric degradation that was similar to what was generally reported in the literature. Biosurfactant release was evaluated for polymer molecular weights (M_w) 40, 80, and 200 kDa, in salt water and deionized water media, each of which showed a high initial burst release of biosurfactant, followed by pulse releases that occurred over the 31 day period. The highest level of biosurfactant release of all the molecular weights tested occurred in the M_w 80 kDa. The release from M_w 40 kDa and M_w 200 kDa was not significantly different (P > 0.05). The results showed that this technology may be useful for enhancing bioremediation of residual hydrophobic organic contaminants (HOC) in estuarine and marine environments.

KEYWORDS:

• biosurfactant
• encapsulation efficiency
• microencapsulation
• Rhamnolipids

ACKNOWLEDGEMENTS

The authors thank Dr. Celestin Youan, from the College of Pharmacy at Texas Technical College, Amarillo, TX, USA for his valuable suggestions to the microencapsulation technique. Our thanks also goes to Mr. Barry Schniepp of Jeneil Biosurfactant Company, for providing the biosurfactants used in this study.

Notes

^a Artihmetic mean within column with the same letter are not significantly different from each other at 5% probability level by Duncan's multiple range test (DMRT).

^b Standard error.