Fig. 3

Product formation is dependent on fungal macromorphology and growth stage. a A schematic representation of pellet macromorphology which can be assessed by a dimensionless morphology number (MN) [45]. MNs varies between 0 (a one dimensional line) and 1 (a perfect circle). Fructofuranosidase and glucoamylase production by A. niger has been negatively correlated with an increasing MN (blue line) [45]; hence, these proteins are efficiently produced by dispersed mycelia. A hypothetical correlation between MN number and productivity is proposed for citric acid and secondary metabolites (red line). b Production of various classes of useful fungal molecules is also dependent on culture growth phase. The blue line depicts biomass accumulation in a hypothetical batch fermentation experiment. Protein and acid synthesis occurs during periods of exponential growth (black box). Formation of some acids occurs following a diauxic shift (orange box), for example citric acid fermentation in A. niger (see main text). Production of most secondary metabolites occurs during periods of low or zero growth (red box)