Biological Synthesis Of L-Ascorbyl Palmitate

As one of important type of additives, ascorbyl palmitate is widely used in cosmetics, medicine and other chemical industries. Enzyme-catalyzed production of ascorbyl palmitate boasts many advantages such as mild reactions, good catalysis effects and low energy consumption. In this paper, The synthesis of ascorbyl palmitate by immobilized lipase Candida sp.99-125was investigated.Fiber membrane was used as the immobilization carriers of the lipase. The lipase was immobilized on fiber membrane by adsorption. Synthesis of ascorbyl palmitate in organic system with high conversion was investigated in this text. Our immobilized lipase from Candida sp.99-125was best for the synthesis system. A series of solvents was studied, such as hexane, pretroleum ether, butyl butyrate, tert-amyl alcohol, acetone, tetrahydrofuran, and acetone was found to be the most suitable solvent for the sake of the enzyme activity and solubility of ascorbic acid.The effect of temperature, concentration of substrates, amount of enzyme were studied in this text. Water in this system played an important role, we controlled system water by molecular sieves. And added molecular sieves can promote this reaction to a new equilibrium.This reaction was carried out at40℃, with2.000g palmitic acid,0.1081g ascorbic acid and0.700g immobilized lipase,0.115g4A molecular sieves was added into the system after36h, the conversion rate of ascorbic acid reached80%and the concentration of ascorbyl palmitate was20g/1after48h. The immobilized lipase was reused about5batches. Soybean oil as a substrate was research in this text. The experiment result showed that soybean oil can be used as donor of fatty acid group to synthesize ascorbyl via transesterification with ascorbic acid in organic media or free solvent catalyzed by immobilized lipase. And conversion rate of ascorbic acid can reach60%.The kinetics of the esterification of vitamin C and palmitic acid catalyzed by an immobilized lipase from Candida sp.99-125were investigated. The kinetics of reaction was suggested to agree with a Ping-Pong mechanism and kinetic parameters of the reaction have been measured.The regioselectivity of the immobilized lipase was a new discovery in this paper, and for the first time, the reason that lead to the decrease in lipase activity was investigated. Regioselectivity of our immobilized lipase was studied by NMR and the result indicated that acylation only took place at the6-hydroxy group.The method for separation and purification of ascorbyl palmitate was investigated. The palmitic acid and ascorbic acid left in the reaction system were removed by circumrotating evaporation and filtration. And the purity of ascorbyl palmitate reached95%after work-up. Last, the pure products determined by IR spectra, HPLC-mass spectrometry,1H NMR spectra and13C NMR. Regioselectivity of our immobilized lipase was studied by NMR and the result indicated that acylation only took place at the6-hydroxy group.