Caffeine-Containing
Emulsion: Influence of the HLB
and Mixing Proportions, the Oil’s Chemical Composition, and
the Existence of Caffeine on Emulsion Properties
This study employs a low-energy emulsification method
to prepare
caffeine-containing emulsions, denoted as Caf-EM. Three different
oils, including coconut, sesame, and grape seed oils, are utilized
along with the surfactants Span 80 and Tween 80. We investigate the
influence of various factors, including (i) the hydrophilic–lipophilic
balance (HLB) and surfactant ratio, (ii) the chemical composition
of the oils, and (iii) the presence of caffeine, on the stability
and size of emulsions. The results indicate that the HLB value and
surfactant ratio are the most crucial factors affecting the emulsions’
stability. The most stable Caf-EM formulation is achieved by combining
mixed surfactants of Span 80 and Tween 80 with an optimal HLB value
of 6.4 at a concentration of 15% (S15 to 6.4) across all oil types.
This specific ratio also leads to significantly smaller emulsion droplet
sizes than other ratios and is the only ratio that produces stable
emulsions even without caffeine (denoted as EM). Notably, formulation
S15–6.4 additionally causes a phase inversion from oil-in-water
(O/W) to water-in-oil (W/O). Furthermore, the presence of caffeine
in the water phase contributes to the formation of smaller and more
stable emulsions. The particle size of Caf-EM is approximately 1.5
times smaller than that of EM. Regarding the oil’s chemical
composition, while there is a discernible trend in emulsion droplet
size (coconut oil > grape seed oil > sesame oil), the differences
within this sequence are insignificant, suggesting that the oil’s
chemical composition does not have a pronounced effect.