| The porcine pancreas lipase (PPLipase) was modified by9nonionic surfactants (Span65,Span85, T40, T65, S770, S970and S1170) in aqueous solution, the optimum modificationconditions of the PPLipase were evaluated. The behavior of the interesterification catalyzedby modified PPLipases in solvent and solvent free systems was studied, and the kineticcharacteristics of interesterification catalyzed by modified PPLipase and PPLipase in solventsystems were also researched.The optimum conditions for9nonionic surfactant were as follows, except the optimumpH of Span65and T65is5.3, the optimum pH for the other surfactant is about7; addingamount of S970, T65and T80, is5%, for S1170, Span85, adding amount10%, as for S770,Span60, Span65, T40, adding amount15%; the optimal stirring time of S1170, Span60, T40,T65and T80is15min, and the others(S770S970, Span65, Span85)30min. The modifiedPPLipase all showed the best catalytic activity at50℃, the transesterification rate of themodified lipases was about10%more than that of the native lipase at50℃. The modificationeffectiveness of S970, Span60, T40were better than others of the same series.In solvent systems, the interesterification was catalyzed by modified PPLipase andPPLipase respectively and the influence of enzyme loadings, water content, reactiontemperature on the enzymatic acyl incorporation and acyl migration were discussed: thechanges of enzyme loadings with5%,10%,15%,10%, the acyl incorporation of theinteresterification catalyzed by modified PPLipase were higher than PPLipase, at the sametime, the acyl migration were lower; water content changed with0.2%,0.4%,0.6%, while thewater content was0.4%, the acyl incorporation of the interesterification catalyzed bymodified PPLipase and PPLipase were all highest, and the acyl migration was lower, theeffects of modified PPLipase were better than PPLipase in the same water content,; anappropriate increase in temperature can help to improve the activity of PPLipase, butPPLipase was denatured and inactive easily in a higher temperature, the reaction velocity ofPPLipase was extremely low and the most of PPLipase has been inactive at70℃, modifiedPPLipase was more resistant to high temperature than PPLipase at the same conditions. In solvent free systems, the interesterification catalyzed by modified PPLipase andPPLipase and the influence of enzyme loadings, water content, reaction temperature, the threefactors on the influence of the enzymatic acyl incorporation and acyl migration werediscussed: within a certain range of enzyme loadings, enzyme loadings which was increasedcan promote the contact between catalyst and reaction substrate, there is a big differencebetween three kinds of modified PPLipase and PPLipase on the reaction velocity, and enzymeloadings were increased further, substrate was saturated by PPLipase gradually, only part ofPPLipase impact in the interesterification, the acyl incorporation level gap by modifiedPPLipase and PPLipase was lower than before; At a certain extent, the water content canimprove reaction velocity, but the reaction balance was not changed and the acylincorporation was the same when the balance was reached; there is a big difference betweenmodified PPLipase and PPLipase on the interesterification activity at low temperature,modified PPLipase can improve reaction velocity at a certain extent, but at high temperature,the difference was not obvious.According to the mechanism of material balance, the interesterification kinetics modelof OOO with Stearic acid catalyzed by PPLipase and modified PPLipase was established insolvent systems. The relationship of component contents, reaction velocity and time werededuced. The average reaction velocity (K) were calculated from the established model.K=8.39×10-5[L2/(mmol, min, g enzyme)] for PPLipase;K=9.34×10-5[L2/(mmol, min, g enzyme)] for T40-PPLipase;K=8.74×10-5[L2/(mmol, min, g enzyme)] for Span60-PPLipase;K=9.39×10-5[L2/(mmol, min, g enzyme)] for S970-PPLipase. |
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