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Abstract
Ascorbyl palmitate was synthesized using a Celite-immobilized commercial lipase (Lipolase 100L) in dimethylsulfoxide (DMSO) as an organic solvent system. Lipase immobilized by surface adsorption onto Celite 545 matrix and subsequently exposed to 1 % glutaraldehyde showed 75 % binding of protein. The Celite-bound lipase was optimally active at 75 °C and pH 8.5 under shaking and showed maximum hydrolytic activity toward p-NPP as a substrate. The bound lipase was found to be stimulated only in the presence of Al3+ and EDTA. All surfactants (Tween-20, Tween-80 and Triton X-100) had an inhibitory effect on lipase activity. The optimization of various reaction conditions of ascorbyl palmitate was achieved considering one factor at a time. The esterification of ascorbic acid and palmitic acid was carried out with 1 M ascorbic acid and 2.5 M palmitic acid in DMSO at 75 °C for 18 h under shaking (120 rpm). Molecular sieves had an important effect on the ester synthesis resulting in an enhanced yield. The by-product (H2O) produced in the reaction was scavenged by the molecular sieves (20 mg/ml) added in the reaction mixture which enhanced the ester yield to 80 %. The characterization of synthesized ester was done through FTIR spectroscopy.
Highlights
Lipases bring about a range of bioconversion reactions such as hydrolysis, inter-esterification, esterification, alcoholysis, acidolysis and aminolysis (Rajesh and Reddy 2013)
The swelling capacity of Celite 545 in water was recorded as 1.9 times
The matrix treated with 1 % (v/v) glutaraldehyde showed 75 % binding/retention of commercial lipase, while the untreated matrix resulted in 61 % binding/retention of lipase
Summary
Lipases bring about a range of bioconversion reactions such as hydrolysis, inter-esterification, esterification, alcoholysis, acidolysis and aminolysis (Rajesh and Reddy 2013). There are many advantages of using enzyme in low water/organic solvent media such as better solubility of substrate and products, simple removal of solvent (most of the organic solvents have lower boiling point than water), reduction in water-dependent side reactions, easy removal of enzyme after reaction since it is not dissolved in organic solvents, better thermal stability of enzyme at high temperature, elimination of microbial contamination, absence of undesirable side reactions and an increased thermal stability of the enzyme in harsh conditions. The stability of biocatalyst in an organic solvent such as DMSO might be attributed to the fact that a thin layer of molecules remain tightly bound to the enzyme acting as a protective sheath along the enzyme hydrophilic surface, allowing retention of native confirmation. Enhancement in enzymatic activity in the presence of organic solvents could be due to some alterations in the catalytic hydrophobic pocket of the enzyme
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