Enzymatic Synthesis Of L-ascorbyl Fatty Acid Esters Under Ultrasonic Irradiation And Comparison Of Their Antioxidant Activity

L-ascorbic acid, a necessary nutrient to keep the ordinary life and function of human body, has been widely used as a natural water soluble antioxidant with high reducing ability, while the application was limited due to its weak solubility in lipidic matrices or lipophilic medium. Derivatives of L-ascorbic acid, with good solubility in hydrophobic medium, showed similar or even better antioxidant effects than L-ascorbic acid.Some L-ascorbyl fatty acid esters could be used to replace the traditional antioxidants in food and cosmetic industry. A series of novel L-ascorbyl fatty acid esters were synthesized by catalization of Novozym? 435 under ultrasonic irradiation.1. The synthesis of L-ascorbyl butyrate, L-ascorbyl hexanoate and L-ascorbyl caprylate catalyzed by Novozym?435 under ultrasonic irradiation were investigated. The synthesis conditions were optimized and structural identification and characterization were confirmed by infrared spectroscopy, electrospray ionization mass spectra, and nuclear magnetic resonance. The product yield reached 68.0%, 55.1% and 73.3%,respectively.2. The synthesis of L-ascorbyl sorbate, L-ascorbyl 10-undecylenate and L-ascorbyl linoleate catalyzed by Novozym?435 under ultrasonic irradiation were investigated. The synthesis conditions were optimized and structural identification and characterization were confirmed by infrared spectroscopy, electrospray ionization mass spectra, and nuclear magnetic resonance. The product yield reached 35.0%, 40.6% and 46.2%,respectively.3. The hydroxyl radical scavenging activity, 1,1-diphenyl-2-picrylhydrazyl(DPPH) radical scavenging activity and reducing power of the L-ascorbyl fatty acid esters were evaluated. The L-ascorbyl saturated fatty acid esters showed better hydroxyl radical scavenging activity, DPPH radical scavenging activity and reducing power than the L-ascorbyl unsaturated fatty acid esters and vitamin E. The hydroxyl and DPPH radical scavenging activity increased with the increase of chain length of fatty acids, and the reducing power became better as well. The L-ascorbyl fatty acid esters showed better hydroxyl radical scavenging activity, DPPH radical scavenging activity and reducing power than L-ascorbic acid, while the butylated hydroxytoluene(BHT) showed better hydroxyl radical scavenging activity than all of the L-ascorbyl fatty acid esters and better DPPH radical scavenging activity and reducing power than L-ascorbyl unsaturated fatty acid esters.4. The oil antioxidant ability of the L-ascorbyl fatty acid esters were evaluated. The oil antioxidant abilityof L-ascorbyl fatty acid esters increased with the increase of chain length of fatty acids and the L-ascorbyl saturated fatty acid esters showed better oil antioxidant ability than L-ascorbyl unsaturated fatty acid esters.BHT showed better oil antioxidant ability than L-ascorbyl unsaturated fatty acid esters, while L-ascorbyl saturated fatty acid esters showed better oil antioxidant ability than L-ascorbic acid and vitamin E.