Co-immobilization of pectinase and glucoamylase onto sodium aliginate/graphene oxide composite beads and its application in the preparation of pumpkin-hawthorn juice.

Co-immobilization of pectinase and glucoamylase onto sodium alginate/graphene oxide beads was achieved by N,N'-dicyclohexylcarbodiimide/N-hydroxysuccinimide as activating agent. The co-immobilized pectinase-glucoamylase (I-PG) prepared under optimal conditions (pH 4.0, 40°C and 35 min) possessed pectinase activity of 1,227.5 ± 36.5U/g and glucoamylase activity of 1,027.2 ± 29.2U/g, with activity recovery of 73.8% and 85.2%, respectively. Both pectinase and glucoamylase in I-PG possessed wider pH tolerance and superior thermal stability to those of their free counterparts. Reusability studies indicated that both enzymes in I-PG retained over 60% of initial activity after six times of reuse. Conditions for the hydrolysis of the pumpkin-hawthorn compound juice by I-PG were optimized using orthogonal experiments. After treatment with I-PG, light transmittance, soluble solids, and reducing sugar content in the resulting juice increased significantly, whereas soluble protein and pectin content decreased appreciably. Therefore, the use of I-PG provided an effective and feasible method for improving quality of the pumpkin-hawthorn juice. PRACTICAL APPLICATIONS: In order to overcome the drawbacks of using free pectinase and glucoamylase, an effective method for the co-immobilization of these two enzymes onto sodium alginate/graphene oxide beads was developed. The co-immobilized pectinase/glucoamylase developed in this study could be applied in the clarification of juice rich in pectin and starch.