Determination of in vitro and in vivo production of polygalacturonase (pg) by storage mold aspergillus niger v. Tieghem, during storage of rice (oryzae sativa l) seeds

Abstract

ABSTRACT:The in vitro and in vivo production of pectic enzyme polygalacturonase (PG) by storage mold of rice Aspergillus niger and the effect of temperature and pH on the activity of the mold were investigated. The result of the assay for the production of polygalacturonase (PG) by the mold in vitro and in vivo showed that the activity of the enzyme when tested viscometrically, using 10% pectin was 142.9 R.V. o C with a value of 111.1 R.V.U each. The optimum activity of the enzyme produced in vitro by the fungus obtained at pH 5 and 6 with a value of 125R.V.U, and at pH 5 with a value of 142.9 R .V. U. in vivo. The activity of the enzyme was least at pH 2, 3, 4, 7,8, 9 and 10 in vitro, and at pH 2,3,8,9 and 10. in vivo with a value of 111.1 R. V. U. @JASEM Polygalacturonase ( PG) E.C 3.2.1.15 is considered to be the main enzyme that degrades pectic substances. It catalyses the hydrolytic splitting of ά -1,4 glycosidic linkages in the polygalachoronide chains of pectic (non-methyl esterified uronide chains) or pectinc acids of the middle lamella into polygalacturonic acids and galacturonic acid chains of smaller molecular size and eventually to monogalacturonic acid. It shows highest activity on pectic acids, whereas activity decreases considerably as the methoxyl content of the substrate increases. Several pathogens produce polygalacturonase (PG) in infected tissue, for example, Hancock and Millar (1965b), showed that Colletotrichum trifolii produced PG. It was also reported to have been produced by Botryodiplodia theobromae by Arinze and Smith, (1979) Barmore and Brown (1981), reported that the enzyme operated optimally at pH 6. Akanu-Ibiam, and Arinze, (1999), reported that the pH for the optimum activity of PG secreted from carrot tissues by F moniliforme was pH 5, while Ibiam and Arinze, (2005), reported that it was pH 5 and 6 for PG secreted by F moniliforme in vitro , and at pH 6 for that secreted in vivo by the same enzyme .Ibiam and Arinze, (2007), also reported that the optimum temperature the activity of PG secreted B oryzae from tissues of rice seeds were pH 6 in vitro and ph 5 and 6 in vivo.This work is aimed at determining the in vitro and in vivo production of pectic enzyme by Aspergillus niger, and the temperature for and pH at which the enzyme operates optimally which will assist in the control of the storage mold. . In vivo production: Homogenates were obtained by removing the tissues rotted by the test fungus with sterile carpel. The rotted tissues were mixed with 0.1M phosphate buffer, pH 7.0 (1g tissue/10ml buffer) containing 0.2M NaCl (to de-absorb proteins from the tissue), and 0.001M ascorbic acid (to prevent oxidation).The extract was prepared by MATERIALS AND METHODS