(b) Untreated vitamin C ester L-ascorbic acid dipalmitate
(c) Oil-treated vitamin C ester
The oil-treated vitamin C was prepared by mixing L-ascorbic acid dipalmitate and a silicone oil (dimethyl polysiloxane-lOOCS) in the weight ratio of 1:1 and then kneading the mixture with a roller mill or a kneader. According to the same procedure, free L-ascorbic acid was also treated.
(d) Preparation of cream samples
To each base was added untreated vitamin C ester or the oil-treated vitamin C ester in an amount of 1% based on the total weight of the base at 70* C. and the resulting mixture was cooled with stirring to about 30° C. to obtain a cream.
(2) Test method
Each cream thus obtained was allowed to stand at —5° C, room temperature and 40° C, respectively, and the amount of L-ascorbic acid dipalmitate or L-ascorbic acid in the cream was determined at regular time intervals by using a high performance liquid chromatogra