Abstract

The effect of spore inoculum level and mycelia morphology on raw starch digesting amylase production by Aspergillus carbonarius in submerged culture was investigated. Shake flask cultures were inoculated directly with spore concentration range of 10⁴ to 10⁹spores/ml. Morphology was differentiated into, pellets, clumps, branched and free filaments. Results on the percentage morphological occurrences revealed that for all tested inoculum a gradual change in morphology was observed as innoculum level increased from 10⁴ to 10⁹spores/ml though pellets predominated. A decrease in the mean main and total hyphal length, mean hyphal growth unit and marginal increase in mean number of tips/mycelium was observed in the mycelia trees as inoculum levels increased from 10⁴ to 10⁹spores/ml. In the aggregated forms, there was a decrease in the mean area, perimeter, roughness and equivalent diameter while mean compactness increased as inoculum increased from 10⁴ to 10⁹ spores/ml. Irrespective of the predominating form a change in morphology was observed. RSDA production appeared to be related to spore inoculum level. Maximum yield was observed at fermentation inoculated with 10⁴ and 10⁵spores/ml where pellets were most dominant. The impact of spore inoculum size on the resulting mycelia morphology was marginal but had a significant effect on RSDA production.

Key words: Aspergillus carbonarius, raw starch digesting amylase, fungal morphology and inoculum.