Résumé
Extracellular tannase and gallic acid were produced optimally under submerged fermentation at 37 0C, 72 h, pH 5.0, 10 percent(v/v) inoculum and 4 percent(w/v) of the agroresidue pomegranate rind (PR) powder by an Aspergillus niger isolate. Tannic acid (1 percent) stimulated the enzyme production by 245.9 percent while with 0.5 percent glucose, increase was marginal. Tannase production was inhibited by gallic acid and nitrogen sources such as NH4NO3, NH4Cl, KNO3, asparatic acid, urea and EDTA. The partially purified enzyme showed temperature and pH optima of 35 0C and 6.2 respectively which shifted to 40 0C and 5.8 on immobilization in alginate beads. Activity of the enzyme was inhibited by Zn+2, Ca+, Mn+2, Mg+2, Ba+2and Ag+. The immobilized enzyme removed 68.8 percent tannin from juice of aonla/myrobalan (Phyllanthus emblica), a tropical fruit, rich in vitamin C and other essential nutrients. The enzymatic treatment of the juice with minimum reduction in vitamin C is encouraging as non enzymatic treatments of myrobalan juice results in vitamin C removal.