Modeling of oligodextran production in an ultrafiltration stirred-cell membrane reactor

The aim of this study was to investigate the types of oligodextrans that could be generated via controlled enzymatic depolymerization of dextran using an endodextranase. An ultrafiltration stirred-cell membrane reactor was employed to provide the means of controlling product molecular size and characteristics. The process was operated in batch mode and the products were recovered as permeates. The effect of enzyme concentration (0.625-62.5 U ml(-1) substrate), substrate concentration (2.5-7.5% w/v), and transmembrane pressure (200-400 kPa), each at three levels, on the product characteristics were studied. The experiments were arranged according to a central composite statistical design. Response surface methodology (RSM) was used to assess factor interactions and empirical models regarding four product response variables (i.e., permeate flux; yield, dextrose equivalent, and oligosaccharide content) were fitted. The fit of the models was found to be good. Permeate flux ranged from 0.01-0.11 (ml cm(-2) min(-1)) and was significantly affected by the interactions among the operating variables. Dextrose equivalent values (DE) ranged from 18-38 with significant interaction between the enzyme concentration and substrate concentration DE increased with increasing enzyme concentration and decreased substrate concentration. Product yields ranged from 25-84% and were principally related to the enzyme concentration. The oligosaccharide content of the products ranged from 27-82% (w/w) and was characterized by significant interactions among the operating variables. The use of RSM for modelling these types of membrane reactors is discussed. (C) 1998 Elsevier Science Inc.