Study On Effects And Mechanism Of Acetaldehyde On The Catalysis Perfomance Of Lipase

Acetaldehyde is an important organic chemical raw material,which has lowrelative molecular mass but high chemical activity. As a by-product generated duringthe lipase-catalyzed reaction,few studies on the effect and mechanism of acetaldehydeon the catalytic activity of the lipase were carried out. In this paper,the in-depthresearch and discussion of effect and mechanism of acetaldehyde on esterification andester exchange reaction were studied to provide a theoretical basis for the lipase basicresearch.The optimal conditions for the hydrolysis reaction lipase-catalyzed were thefollowing: temperature40°C, pH7.5, substrate concentration62.3mmol/L andreaction time10min.The hydrolysis rate of lipase-catalyzed reaction rose first andthen dropped. The maximum activation concentration of acetaldehyde onlipase-catalyzed hydrolysis reaction was0.2215mmol/L. Acetaldehyde show lessimpact on the optimum temperature,but make the optimum pH shift to the alkalinedirection. In the presence of acetaldehyde, the infrared, UV and fluorescence spectraof lipase were significantly enhanced and offseted,which improve the degree ofsecondary order structure of lipase molecule and directly stabilize themicro-environment and conformation of the enzyme molecule. The kinetic dataindicated that the Vmax value of CRL enzyme increased and Km values declinedwhen treated by low concentrations of acetaldehyde,which descripted that in thepresence of acetaldehyde the maximum reaction rate of the reaction improved, at thesame time,enhanced the affinity of the enzyme with substrate.The optimal conditions of lipase-catalyzed esterification were the following:temperature35°C, enzyme concentration5%, methanol to oil molar ratio1:1and thereaction time7.5h. The acetaldehyde showed inhibition for the esterification activityof lipase,which contained Both physical and chemical action. The maximuminhibition concentration of acetaldehyde was1.772mmol/L and it is a noncompetitiveinhibition type. The inhibition intensity was constantly declined with the increasingtemperature and was enhanced with the increasing hydrophobic organic solvent.When the metal ions with acetaldehyde coexist in system, a dual inhibition onenzymes exhibited stronger than when they exist independently. The mechanism ofinhibition by metal ions with acetaldehyde is for further study.The optimal conditions lipase-catalyzed transesterification reaction were thefollowing: temperature35°C, the concentration of enzyme5%,the methanol to oil molar ratio5:1and the reaction time15h. The acetaldehyde inhibit thelipase-catalyzed transesterification activity when the concentration of acetaldehyde2.2150mmol/L showed the strongest inhibition on lipase. The higher of thehydrophobic organic solvent, the stronger of the inhibition of acetaldehyde on enzymeactivity. Lipase-catalyzed transesterification reaction showed repeatability,while therecovery of enzyme remained high level activity. The recycling activity after the firstbatch of lipase treated by acetaldehyde was still suppressed, which indicated that theAcetaldehyde influenced lipase-catalyzed transesterification mainly through chemicalcombination.