Amylolytic enzyme production by immobilised cells of 'Aspergillus niger'

Abstract

A strain of Aspergillus niger, isolated from rotting cassava tubers, has been immobilised in beads of calcium alginate (1 percent, w/v) and used to produce amylolytic enzymes. The optimal operating conditions (cell concentration and gel composition of the immobilised system, temperature of incubation, initial pH of the medium) have been investigated. Amylolytic enzyme production was associated with the cell growth within the calcium alginate beads. The growth pattern of Aspergillus niger cells trapped in the calcium alginate gel has been studied. An early phase of exponential growth followed by a phase of decelerating growth rate was observed. The explanation for this growth pattern has been discussed. By operating the immobilised cell system under optimised conditions a higher level of amylolytic enzyme production than that obtained with a free cell system was achieved. A better operational stability for the immobilised system was demonstrated. The continuous production of amylolytic enzymes by the immobilised cells of Aspergillus niger has been investigated. Using a nitrogen-limited medium, it was possible to maintain a relatively high enzyme productivity during a 12 day- period of continuous operation. The thermostability, storage stability, pH and temperature activity profiles of the crude enzyme broth from the immobilised cell culture, and their comparison with these characteristics for enzyme broth from a free cell culture, have been studied. The conversion of raw (uncooked) cassava starch to glucose syrup and, in the presence of yeast cells, its further fermentation to ethanol, have been investigated using culture liquid from immobilised cells. Also, the immobilised cell system has been employed as a possible treatment system for starch-containing wastewater.