Study on nano-emulsion stabilized by mixtures of Phosphatidylcholine and Lysophosphatidylcholine using NMR 

Paphawee Nantarajit1, Natdanai Falaungwithayakul1, Ian Norton2, Shingo Matsukawa1, 

1 Graduate School of Marine Science and Technology, Tokyo University of Marine Science and Technology, Tokyo, Japan 
2 School of Engineering, University of Birmingham, Birmingham, UK

Lecithin is one of phospholipids which is found in egg yolk and soybean, and widely used in food industry as an emulsifiers.  Recently, we found a transitional formation of wormlike micelle in the mixture of spherical micelle of lysophosphatidylcholine (LPC) and planner micelle of phosphatidylcholine (PC) were induced by heating because it consists of mono-, di-acylglycerol as a non-polar moiety and choline as a polar head group1. This  suggested that the heating induced the comicellization in the mixed solutions of PC and LPC, which is suitable to the wormlike structure. From this phenomena, we hypothesis that PC and LPC migrate between the surface of oil droplets and micelles leading to the most stable ratio at the W/O emulsion surface. This optimal ration is expected to improve the stability of emulsions. In this study, we tested this hypothesis for nano-emulsions using NMR.

PC and LPC based-emulsions were prepared using high-energy emulsification methods. Emulsion size and droplet size distribution were measured by dynamic light scattering (DLS) techniques. Comparison of the droplet sizes showed that PC and LPC, mixtures of PC/LPC,. and different emulsification times influenced the droplet size distribution of emulsions and emulsion stability.  Increasing the emulsification time of all surfactants resulted in  decreasing the size distribution of emulsions  to be smaller.  Because it has been reported that the mobility of headgroup played an important role in the stability of emulsion2,  we have carried out 31P-NMR  measurements to investigate the interaction between phospholipids and oil in emulsions, and the result will be discussed. The molecular mobility of phospholipids and migration of them at the interface between oil and water phase using NMR will also be discussed.

References:
1	N. FAFAUNGWITHAYAKUL, U. KLINKESORN, T.BRENNER, N. VICHAKACHARU and S. MATSUKAWA. Thermally Induced Gelation of Mixed Phosphatidylcholine Aqueous Solution Containing Wormlike Micelle Structure. Japan J. Of Food Engineering, 15(4),233-242(2-14).
2 K. CHIBA and M. TADA. Study of the Emulsion Stability and Headgroup Motion of Phosphatidylcholine and Lysophosphatidylcholine by 13C- and 31P-NMR. Agric. Biol. Chem., 53 (4), 9951001, 1989.