Stability of vitamin A in oil-in-water-in-oil-type multiple emulsions

The stability of vitamin A was studied in three different emulsions: oil-in-water (O/W), water-in-oil (W/O), and oil-in-water-in-oil (O/W/O). The stability of retinol (vitamin A alcohol) in the O/W/O emulsion was the highest among the three types of emulsions; remaining percentages at 50 degrees C after 4 wk in the O/W/O, W/O, and O/W emulsions were 56.9, 45.7, and 32.3, respectively. With increasing peroxide value of O/W and W/O emulsifiers, the remaining percentage of vitamin A palmitate and retinol in the emulsions decreased significantly, indicating that peroxides in the formulae accelerate the decomposition of vitamin A. Organophilic clay mineral tan oil gelling agent and a W/O emulsifier) also affected the stability of retinol; synthesized saponite was better than naturally occurring bentonite for retinol stability. The stability of retinol in the O/W/O emulsion increased with increasing inner oil phase ratio (phi(i)), whereas in O/W it was unaffected by phi(i). Encapsulation percentage of retinol in the O/W/O emulsion, the ratio of retinol in the inner oil phase to the total amount in the emulsion, increased with increasing phi(i). The remaining percentage of retinol in the O/W/O emulsion was in excellent agreement with encapsulation percentage, suggesting that retinol in the inner oil phase is more stable than that in the outer oil phase. Addition of antioxidants (tert-butylhydroxytoluene, sodium ascorbate, and EDTA) to the O/W/O emulsion improved the stability of retinol up to 77.1% at 50 degrees C after 4 wk. We conclude that the O/W/O emulsion is a useful formula to stabilize vitamin A.