Enzymatic Synthesis Of L-ascorbyl Fatty Acid Esters And Their Anti-oxidation Characterization

L-ascorbic acid and L-ascorbyl salt derivatives are water-soluble antioxidants. However,because of the poor oil solubility, they were limited in their application in fatty foods, cosmetics and other fields. The L-ascorbyl fatty acid esters, synthesized by L-ascorbic acid and fatty acids (or aliphatic esters), not only can keep antioxidant activity of L- ascorbic acid, but also are soluble in animal fats and vegetable oils. Therefore, L-ascorbyl fatty acid esters are widely used in food, cosmetics, and pharmaceuticals fields. But, so far, the synthetical techniques of L-ascorbyl fatty acid esters are most chemical methods, and they possess such shortcomings as difficulties in products quality control and purification, and pollution discharge. In this work, L-ascorbyl fatty acid esters synthesized in organic solvent media with immobilized lipase as catalyst was discussed, with methyl palmitate, fatty acids and soybean oil as acyl donors. The main results were as follows:1. Reversed Phase High Performance Liquid Chromatography Determination (RP-HPLC) method was optimized, and it could simultaneously determine the contents of L-ascorbic acid and L-ascorbyl fatty acid esters precisely.2. Based on the results of single factorial experiments, the Response Surface Method (RSM) was employed to further optimize the reaction conditions. The optimum conditions were: tert-butanol 10 mL, the molar ratio of L-ascorbic acid and methyl palmitate 1:3.8, reaction temperature 54.6 oC, reaction time 17.2 h and 5.2 wt% of Novo 435 lipase dosage (w/w, based on the total mass of L-ascorbic acid and methyl palmitate). Under the optimal conditions, the recovery ratio of L-ascorbyl palmitate was up to 79.5%. Meanwhile, the prediction value was validated with oleic acid, linoleic acid and soybean oil as acyl donors, and different kinds of L-ascorbyl fatty acid ester products were synthesized.3. The anti-oxidative properties of different kinds of L-ascorbyl fatty acid esters were evaluated by four methods: scavenging effect on hydroxyl radical, superoxide anion radical, and reducing power and delaying lipid oxidative degradation. Their anti-oxidative properties were also compared to the common antioxidants of TBHQ, BHT, BHA, VC and VE. The results showed that the L-ascorbyl fatty acid esters had good anti-oxidative property in scavenging effect on hydroxyl radical, reducing power and delaying lipid oxidative degradation, but were not as good as the current antioxidants in scavenging effect on superoxide anion radical.