Study On The Lipase-catalyzed Synthesis Of L-ascorbyl Laurate In Organic Solvent

L-ascorbyl fatty acid esters are used widely as natural additives in foods and cosmetics due to their antioxidant activity. Currently, the saturated ascorbyl fatty acid esters used in the industry are all chemically synthesized. By contrast, enzyme catalyzed synthesis could be performed under milder conditions such as at lower temperatures. However, due to the low solubility of the reaction substrate in organic solvent, the industrialization of the enzyme catalyzed synthesis of L-ascorbyl fatty acid esters was limited. In this study, the technique for continuous lipase-catalyzed synthesis of L-ascorbyl fatty acid esters was investigated by designing a packed-bed reaction system in order to raise the yield.L-ascorbyl laurate was synthesized in acetone solvent catalyzed by lipase Novo 435 at 50℃with a substrates ratio (lauric acid : L-ascorbic acid) of 4:1. The separation and purification of the synthesized ester was carried out by organic solvent extraction, silica gel column chromatography, and high performance liquid chromatography (HPLC), respectively. The purities of final products separated by these three methods were 86.5%, 90.4% and 95.5%, respectively. The purified product was then subjected to mass spectrometry(MS)and nuclear magnetic resonance(NMR) analysis.For large-scale production in industry, a continuous reaction would be preferred. In this study, a packed-bed reaction system was designed to continuously synthesize L-ascorbyl laurate. The influences of the flow rate of substrate solution, the molar ratio of substrates, and the addition of molecular sieves were emphatically studied in detail. The optimized reaction conditions were as follow: flow rate 0.37 mL/min at 50℃with the initial molar ration of substrates 6:1. At these optimized reaction conditions, the product concentration could be as high as 24.2mmol/L, and the productivity could reach 4.62g/( L·d). Furthermore, the reaction system would be suitable for the continuous synthesis of the other acyl L-ascorbates and sugar esters as well.The CMC of L-ascorbyl laurate determined by Du Nouy ring method was 0.1 mmol/L. Finally, the determination of DPPH·and ABTS·+ free radical scavenging ability showed that there is significant differences between DPPH·free radical scavenging ability of L-ascorbyl laurate, L-ascorbyl palmitate and L-ascorbic acid while the acyl L-ascorbates were better than L-ascorbic acid. But there is no significant difference was found between ABTS·+free radical scavenging ability and metal (copper ion) chelating ability of these compounds.