Antioxidative Properties of Ascorbic Acid and Acyl Ascorbates in ML/W Emulsion
2010
Watanabe, Yoshiyuki | Nakanishi, Hirofumi | Goto, Natsuki | Otsuka, Kyosuke | Kimura, Toru | Adachi, Shuji
Octanoyl, dodecanoyl and hexadecanoyl ascorbates were synthesized by the condensation of ascorbic acid and the corresponding fatty acids in acetone using an immobilized lipase from Candida antarctica. The oxidation process of methyl linoleate (ML) as an oil droplet in the ML/W emulsion with ascorbic acid or acyl ascorbate was measured at 40 °C, and their antioxidative properties were examined. Hydrophilic proxidant, AAPH, or lipophilic proxidant, AMVN, was added to the water or oil phase to investigate the properties, and the kinetic parameters for the oxidation expressed by the Weibull equation were evaluated. It was suggested that most of the ascorbic acid molecules in the emulsion would be present in the water phase due to its high hydrophilicity and suppress the AAPH-induced oxidation on the interface between the water and oil phases. Dodecanoyl and hexadecanoyl ascorbates would be dissolved in the oil phase and contribute to the suppression of the oxidation in the oil phase rather than on the interface. Octanoyl ascorbate with a HLB number of 11.8 would be in both phases. Regardless of the presence and type of the ascorbate, the rate constant, k, of the Weibull equation decreased as the pH of the water phase increased.
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