| Enzyme treatment has become an indispensable process to producing apple juice.Pectinase was used to improve the juice yield and juice stability. It can also avoid "after haze". For the difficult recovery and unstable characters, free enzyme is hard to treat apple juice, on the other hand the astonished price prevents purified enzyme from industrialization. In this paper, two carriers for immobilization of pectinase and measuring method of pectinase activity is studied, the results were showed as follow: ⑴The measuring method which improved in this paper is more simple, accurate and also has good reproducibility. It is much more efficient than QB1502 and other methods, especially in determinating the activities of immobilized pectinase and high activity pectinase. ⑵The optimal conditions of immobilized pectinase on chitosan through orthogonal analysis were as follow:glutaraldehyde concentration 5%,volume of enzyme 1ml,reaction time 1.5h.Factors of enzyme volume and glutaraldehyde concentration have significant effects on recovery. ⑶When the condition is Fe3+: Fe2+1:1, stirring speed 500r/min, reaction temperature 40℃,the particles which are the smallest and strongest were got.The orthogonal ratation combination design was employed to establish mathematical models for immobilized enzyme. The equation is: Y|^ =56.25429+9.94534X2+7.35225X3-17.58314X12+3.82452X22-5.33750X1X2, Y|^ as recovery of enzyme,X1,X2,X3 as volume of chitosan, magnetic Fe3O4 particles and glutaraldehyde respectively. There was a interaction between X1 and X2. ⑷compare free pectinase with immobilized pectinase on magnetic chitosan microspheres are as follow: the optimal reaction temperature of pectinase is 50℃,but immobilized is between 55℃60℃;the optimal pH is 3.5 and 4.0 respectively. The result showed that the stability of immobilized pectinase are better than free pectinase. ⑸In this study, the kinetics of pectinase was studied, including free pectinase and pectinase which was immobilized on magnetic chitosan microspheres.Kinnetic constant were found as Km 5.01 for free enzyme and Km 2.49 for immobilized pectinase.So the activation energy of reaction catalyzed for free pectinase is higher than immobilized pectinase.
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