3.2. Characteristics of microemulsion
The physico-chemical parameters of hesperetin microemulsions
were measured and are listed in Tables 2 and 3.
The droplet size of microemulsion was small with all the formulations having
a mean size between 101.5 and 233.0 nm.
The electrical conductivity of IPM (oil phase) and doubled water were 0 and 0.6S/cm
respectively.
As shown in Table 2, the electrical conductivity of all
drug-loading microemulsions ranged from 0.5 to 87.2S/cm.
The electrical conductivity of microemulsions was significantly higher than the oil phase.
Moreover, electrical conductivity of microemulsions increased by the increase in the level of aqueous phase or the polarity of co-surfactant.
The increase in electrical conductivity might be due to the increase in dissociation of surfactant as a function of water content (Baker et al., 1984).
These results were in accordance with a previous study (Sintov and Shapiro, 2004)
and indicated that the microemulsions were oil-in-water type.
The solubility of hesperetin in IPM and water were 385.4 and 8.03g/mL respectively.
All microemulsion formulations containing 1% hesperetin in this study were clear and transparent solutions; no precipitate was observed, indicated that microemulsion
can increase the solubility of the drug (Teichmann et al., 2007).
Microemulsion stored at room temperature for 2 months showed no change in clarity, phase behavior and particle size (data not shown).
The concentration of hesperetin in microemulsion was above 98.0±1.5%, showing there was no degradation.