Effect of substrate concentration on broth rheology and fungal morphology during exo-biopolymer production by Paecilomyces japonica in a batch bioreactor

The influence of pellet morphology of Paecilomyces japonica on fermentation broth theology and exo- biopolymer production: was investigated. The subst rate concentration was varied between 20 and 80 g/liter while running the f ermentation at a high aeration of 3 vvm. The specific growth rate of Paecil omyces japonica and exo-biopolymer production was found to be optimum with a substrate concentration of 40 g/liter of sucrose. Rapid formation of pell ets was observed after the first day of fermentation, which slowly increase d in size, hairiness and roughness. This, together with the increase in bio mass concentration, altered the transport characteristics and the broth the ology to pseudoplastic nature, in turn, influenced exo-biopolymer productio n. At mild agitation, high aeration and optimum substrate concentration, pe llets were the most predominant morphological form compared to free mycelia . Compact pellets with least hairiness and roughness, which improved the fl ow characteristics of the fermentation broth were observed at 40 g/liter of sucrose and hence regarded as the most productive morphological form. (C) 2001 Elsevier Science Inc. All rights reserved.