Structure-activity Relationship Of Food-grade Glycerol Monolaurate-based Microemulsion Systems

Glycerol monolaurate, the monoester of lauric acid, is a derivative extracted from coconut oil and has been designated by FDA to be a GRAS food additive. It is well-known as surfactant like lipid with the greatest overall antimicrobial activity of all lipids evaluated as antimicrobials. However, the poor solubility of glycerol monolaurate in water, glycerol and other common solvents leads to difficulties in its use in food industry. The problem can be solved by loading it in microemulsion system, as reported by our lab in last few years. This study was conducted to figure out the relationship of different microstructures (W/O, bicontinuous, O/W) of the prepared U-type microemulsion systems and their antimicrobial activities against Staphylococcus aureus and Escherichia coli.The microstructure transition of the U-type microemulsion system was investigated by differential scanning calorimetry, dynamic light scattering and freeze-fracture transmission electron microscope. The antimicrobial activities of the W/O, bicontinous and O/W microstructures were studied by the kinetics of killing method with a further gene chip analysis on antimicrobial mechanisms.The DSC results showed that with the increasing content of water, the microemulsion microstructure converted from W/O (0-33mass%water) to bicontinuous (33-40mass%water), and finally O/W (40-100mass%water), while the particle size decreased in corresponding to the DLS and FF-TEM observations. The kinetics of killing results showed that the antimicrobial activities of the microemulsions reduced as a microstructure transition from W/O to O/W, with a major contribution of the microemulsion vehicles, composed of Tween20and Ethanol, and the used oil glycerol monolaurate. As indicated by the gene chip results, the nanoscale vehicles enhanced the antimicrobial activity of glycerol monolaurate by modulating some specific genes expression in microorganism cells, leading to a rapid viability loss.These results will be of great significance to provide a guideline in designing the food-grade antimicrobial microemulsion structures, and have promising applications in food industry in future.