Reload Index (ZRiChK UMCS)
ANTIOXIDANTS ACTIVITY IN OIL-IN-WATER MICROEMULSION STABILIZED BY ANIONIC SURFACTANT SYSTEM
DEPARTMENT OF RADIOCHEMISTRY AND COLLOID CHEMISTRY
It is well known that the antioxidation activity of some species in homogenous solutions may not be the same as that in heterogeneous media.In the present paperwe consider antioxidant action in microemulsions. In our investigations we chose the O/W microemulsion formed by water/ pentanol/ sodium dodecyl sulfate.
We investigated the atmospheric oxidation of antioxidants of different solubility in water i.e. vitamin C (H2A, AA), propyl gallate (both species can be easily dissolved in water), vitamin E (α-tocopherol, α-T) (fat-soluble species) and β-carotene (which is totally non-polar and completely insoluble in water) in microemulsion.
From our own experiment and literature information it follows that all considered antioxidants i.e. vitamin C, propyl gallate, vitamin E and β-carotene are solubilized in chosen SDS surfactant systems.
We found that vitamin C can be solubilized up to 60% in the microemulsion region formed in the SDS/ pentanol/ water system.
Taking into account the fact that the water solubility of propyl gallate and vitamin C is similar, one can expect that, like vitamin C, propyl gallate is easily dissolved in SDS micellar solutions and in the O/W microemulsions studied. Propyl gallate could be easily solubilized in SDS solutions, in the palisade layer formed by alkyl chains of surfactant molecules in their association structures.
Microemulsions with small size particles and high resistance to oxidation in air can be obtained by solubilization of vitamin E in non-ionic surfactant solutions, whereas solubilization in sodium dodecyl sulfate solutions results in forming emulsions having small size particles but lacking stability against oxidation.
A number of studies have indicated that carotenoids act as antioxidants in solutions, micelles and liposomes. It was proved that hydrocarbon carotenoids, such as β-carotene are randomly distributed within the hydrophobic part of micelles and membranes.
The main interest of the present paper is the interdependence of the antioxidant solubility character (sometimes identified with hydrophobicity) and its behaviour in O/W microemulsions.
Among the antioxidants investigated vitamin C (water-soluble species) turned out to be the best in O/W microemulsion (Fig.1), much more beater than propyl gallate (Fig. 2).
We found stimulating (not protecting) action of vitamin C towards vitamin E oxidation (Fig. 3).
b-Carotene (totally non-polar, fat-soluble species) solubilized in O/W microemulsion was more resistant to oxidation than other antioxidants in air (Fig. 4). Vitamin C does not influence the b-carotene behaviour; in the absence and presence of vitamin C its action is similar.
Figure 1. The kinetics of 0.002% vitamin C Figure 2. The kinetics of 0.002% propyl gallate
atmospheric oxidation in O/W microemulsion atmospheric oxidation in O/W microemulsion.
formed by SDS, pentanol, water. Remainder of propyl gallate in the system.
Remainder of vitamin C in the system.
Figure 3. The kinetics of 0.015% vitamin E Figure 4. The kinetics of 0.0005% b-carotene
atmospheric oxidation in the presence atmospheric oxidation in O/W microemulsion. 0.002% vitamin C in O/W microemulsion. Remainder of b-carotene in the system.
Remainder of vitamin E in the system. (The solid line are drown to help the eye).