STABILITY AND RELEASE KINETICS OF NATURAL OIL MICROEMULSIONS 27 volume was 20 μL and the detecting wavelength was 260 nm. The analytical method was validated according to the International Conference on Harmonisation (ICH), now named the International Council for Harmonisation (ICH), guidelines (18). RESULTS AND DISCUSSION FATTY ACI DS IN THE STUDIED OILS The types and amounts of fatty a cids in virgin coconut oil and olive oil are presented in Table I. In addition, double bonds in all unsaturated fatty acids found in both oils were in cis confi guration. The results showed that virgin coconut oil could be classifi ed as saturated oil because it predominantly contained saturated fatty acids such as lauric acid (48.102%) and myristic acid (19.140%), whereas olive oil could be regarded as unsaturated oil because it mainly contained oleic acid, an unsaturated fatty acid (71.530%). The main components of both investigated oils were in agreement with a previous report (19) however, slight dif- ferences were found because of dissimilar geographic sources and extraction techniques. CHARACTERISTICS OF NICOTINAMIDE- LOADED MES Four blank MEs (designated as ME C1, MEC2, MEO1, and MEO2) were selected from four ME regions as exhibited in Figure 1 for further incorporating with nicotinamide. Table I Fatty Acid Composition in the Studied Virgin Coconut Oil and Olive Oil Fatty acid (%) Lipid numbers C:Da Virgin coconut oil Olive oil Saturated type Caprylric 8:0 5.897 0.009 Nonanoic 9:0 0.014 0.013 Capric 10:0 5.814 0.000 Undecanoic 11:0 0.024 0.000 Lauric 12:0 48.102 0.000 Tridecanoic 13:0 0.032 0.000 Myristic 14:0 19.140 0.025 Pentadecanoic 15:0 0.010 0.007 Palmitic 16:0 8.978 11.320 Heptadecanoic 17:0 0.000 0.069 Stearic 18:0 3.082 2.786 Behenic 22:0 0.000 0.122 Lignoceric 24:0 0.000 0.030 Unsaturated type Palmitoleic 16:1 0.000 1.070 Oleic 18:1 5.775 71.530 Linoleic 18:2 1.026 10.968 Linolenic 18:3 0.000 0.633 Gondoic 20:1 0.000 0.275 Erucic 22:1 0.000 0.022 a C and D represent numbers of carbon atoms and double bonds in the fatty acid, respectively.
JOURNAL OF COSMETIC SCIENCE 28 The studied blank MEs are summarized in Table II. Virgin coconut oil could form MEs because its medium-chain fatty acids could easily penetrate into the interfacial fi lm (20). Although olive oil contained high amount of oleic acid, a long-chain fatty acid, it could form MEs because of the structural similarity between its fatty acid chain and oleate hydro- phobic tails of Tween 80 as well as Span 80 (21). All obtained 3% w/w nicotinamide -loaded MEs (designated as MEC1-N, MEC2-N, MEO1-N, and MEO2-N) were clear yellowish liquids. Under polarized light microscope, all samples showed no birefringence (data not shown), indicating the isotropic property Figure 1. Pseudoternary phase diagrams and points of blank MEs in ME regions (shaded areas) of the systems consisted of (A) 0.6:0.4 Tween 80:Span 80/virgin coconut oil/water, (B) 0.7:0.3 Tween 80:Span 80/virgin coconut oil/water, (C) 0.6:0.4 Tween 80:Span 80/olive oil/water, and (D) 0.7:0.3 Tween 80:Span 80/olive oil/water. Table II Composition of Blank MEs Formulation S:CoS ratio (Tween 80:Span 80) Oil Composition (% w/w) S:CoS Oil Water MEC1 0.6:0.4 virgin coconut oil 50 45 5 MEC2 0.7:0.3 virgin coconut oil 50 45 5 MEO1 0.6:0.4 olive oil 50 45 5 MEO2 0.7:0.3 olive oil 50 45 5
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