Quantitative assessment of the impact of the type of inoculum on the kinetics of cell growth, substrate consumption and pigment productivity by Penicillium purpurogenum GH2 in liquid culture with an integrated stochastic approach

Natural ingredients are in demand and microbial processes to produce biocolourings are thus being developed. Penicillium spp. is particularly interesting for food applications. While microbial growth would be enhanced by using mycelium as inoculum, studies aimed at optimising pigments yields produced by Penicillium spp. have used spores as inoculum. A quantitative comparison of the pre-culture method for producing pigments by P. purpurogenum GH2 is provided in this work. Data analysis showed that simple growth models do not provide a suitable description of the fermentation process with mycelium as inoculum, which requires accounting for the effect of cell death. Probability density functions were applied to describe cell growth, substrate consumption and pigment production jointly and accurately. Specific production was 51% higher using mycelium as inoculum instead of spores, reaching a highest production of pigments with 10% (v/v) initial concentration being optimal (10.60 ± 0.40 units of Optical Density at 500 nm). Productivity of pigments per hour was 55% higher using mycelium as inoculum compared to spores. Three stochastic distributions provided equally good quantifications of all data (normal, gamma and Weibull). The three variables could be described by a same distribution function, with biomass being related to both live cells and accumulated dead residue.