No abstract

The effect of alpha-tocopherol and its acetate on the membrane structure of egg yolk phosphatidylcholine (egg PC) dispersions was investigated using phosphate-31 nuclear magnetic resonance (31P-NMR) and small-angle X-ray diffraction. The incorporation of alpha-tocopherol into egg PC dispersions induced a change in the 31P-NMR spectrum from a multilamellar bilayer line shape to a hexagonal HII one. The phase transition by alpha-tocopherol was also confirmed by small-angle X-ray diffraction analysis. The amount of hexagonal HII phase increased with increase in concentration of alpha-tocopherol. Egg PC dispersions containing a molar ratio of 0.8 of alpha-tocopherol gave a 31P-NMR spectrum of an approximately hexagonal HII type at 37 degrees C. The amount of hexagonal HII phase increased with increasing temperature, indicating that the alpha-tocopherol-induced phase transition is thermotropic and that the transition temperature of egg PC membranes from the lamellar to the hexagonal HII phase is lowered by alpha-tocopherol. The incorporation of alpha-tocopherol acetate did not induce any phase transition. This fact indicates that the hydroxyl group of alpha-tocopherol may play an important role in the hexagonal HII phase formation of egg PC dispersions.

Gumarabic, a widely used emulsifier, stabilized the substrate of lipase in an emulsion of oil and enhanced the lipase reaction. Pectin, a well-known gelling agent, destabilized the emulsion, and decreased the plasma levels of cholesterol in rats. Little effect of gum arabic on the cholesterol concentration of plasma and liver was observed. These findings might indicate the differences between the effects of gum arabic and pectin on the stability of emulsification and the activity of lipase in vivo.

No abstract

No abstract