preparation and properties of immobilized naringinase in polyvinyl alcohol copolymer carrier for debittering of citrus juices

Naringin a bitter compound in citrus can be converted to a nonbiter fom by enzyme hydrolysis. Naringinase from gamma irradiated enhanced Aspergillus nigro-AH3. γ 20 isolate was partoally purified by various methods and the specificacitivty of 6.1 units per mg protein was obtained. The enzyme was immobilized by entrapment in polyvinyl alcohol / polyacrylamide (PVA/PAAm) copolymer hydrogel carrier produced by gamma radiation polymerization. The activity of the immobilized enzyme was elevated with increasing PVA content in the copolymer carrier to reach its maximum value at PVA/PAAm composition ratio of (60.40, v/v%). The yield of immobilization was highest 95% and yield of activity was 91.1%, when 1 mg naringinase enzyme was immobilized in 1 ml of hydrogel matrix. Some enzymatic and compared with those of the solube free enzyme. The optimal pH of the immobilized enzyme was shifted 0.5 pH units to the alkaline side of that of the soluble free enzyme. Also the optimum temperature was shifted from 50 C degree to 60 c degree and the activation energy of reaction (EA) was markedly decreased from 21.52 to 10.74kcal/mol by immobilization. The influence of the diffusion is reflected in the kinetic parameters Km and Vmax. The application of kinetic parameter of the immobilized enzyme optimized with pure naringin solution and bitter orange juice resuled in about 83.2% and 72.0% debittering after 8 h and 12 h incubation during batcheise operation, respectively. The process has operational versatility from the broad pH and temperature optima and affords highest efficiency and stability during application in debittering of bitter orange juice because it is recycled consecutively 14 times before retaining only about 50 % efficiency. These data can be used for future improvements in debittering of citrus fruits products