Suppressive Effect of Decanoyl Ascorbate on the Oxidation of Fish Oil Encapsulated with a Polysaccharide

Abstract

6-O-Decanoyl l-ascorbate, which was synthesized by the immobilized lipase-catalyzed condensation of decanoic and l-ascorbic acids in acetone, was used for the microencapsulation of fish oil with maltodextrin (MD), gum arabic (GA), or soluble soybean polysaccharide (SSPS). The oxidation processes at 65℃ and 12% relative humidity of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in the encapsulated fish oil were measured, and kinetically evaluated using the Weibull model. The oxidative stabilities of EPA and DHA in the microencapsulated fish oil were high, in the order of SSPS > GA > MD. Decanoyl ascorbate suppressed the oxidation of EPA and DHA in each system. It was indicated that the contribution of high concentrations of decanoyl ascorbate to the oxidative stability of the encapsulated fish oil is attributable to its antioxidative ability, which was due to the ascorbyl moiety in the decanoyl ascorbate molecule, but not to its emulsifying ability. In addition, it was found that the antioxidative effect of decanoyl ascorbate on the acids in the system sensitive to oxidation, such as in bulk and microencapsulated with MD, was high. Therefore, when using wall materials with a low suppressive ability for oxidation of the encapsulated oil, the application of decanoyl ascorbate would be effective.Keywords: decanoyl ascorbate, oxidation, fish oil, microencapsulation, polysaccharide *To whom correspondence should be addressed. E-mail: adachi@kais.kyoto-u.ac.jp IntroductionMicroencapsulation of lipids, as a core material, with a wall can improve the storage stability of lipids (especially oxidative stability), handling of the core material, and can provide the core material with additional functions (Matsuno and Adachi, 1993;Gibbs et al., 1999). Microencapsulation includes two steps: the first is the emulsification of the core material, such as a lipid, with a dense solution of a wall material, and the second is the drying of the emulsions. Saccharides with low and high molecular masses, proteins and other polymers have been used as wall materials. Spray-drying is the general technique for preparing microcapsules.l-Ascorbic acid is a water-soluble vitamin known as vitamin C. It is widely used as an additive in foods and cosmetics due to its strong reducing ability. The lipase-catalyzed synthesis of 6-O-monoacyl ascorbate, through the condensation of ascorbic acid and a fatty acid in an organic solvent, has been reported (Humeau et al., 1995;Yan et al., 1999). The enzymatic synthesis of acyl ascorbates would be more advantageous than a chemical method because of the simplicity of its reaction process and its high regioselectivity. Acyl ascorbate, which consists of ascorbic acid and a fatty acid as the hydrophilic antioxidant and lipophilic group, respectively, is an amphilic antioxidant. It has been reported that 6-Opalmitoyl ascorbate has antitumor activity and metastasisinhibitory effects (Miwa and Yamazaki, 1986;Nagao et al., 1996). Thus, acyl ascorbate is expected to be a useful food additive. We also syn...

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