Apostolis A. Koutinas

Kinetic parameters of Aspergillus awamori in submerged cultivations on whole wheat flour under oxygen limiting conditions

Abstract The kinetic parameters of fungi like Aspergillus awamori may vary significantly according to culture conditions, such as oxygen and fermentation media. The knowledge of maximum growth rate and growth yields is necessary for process optimisation, modelling and scale-up. The measurement of such parameters is hindered on fermentations where complex, heterogeneous medium is utilised. This study focuses on the determination of kinetic parameters such as maximum specific growth rate (0.28xa0h−1) and growth yields on substrate (0.31xa0gxa0g−1) and oxygen (0.22xa0gxa0g−1) for A. awamori growing under oxygen limiting conditions on whole wheat flour in submerged culture. The low growth yields indicated the effect of oxygen depletion on fungal kinetic parameters. A specific glucoamylase production of 72xa0Uxa0g−1xa0h−1 has been observed. The unstructured mathematical model used to simulate fermentation variables takes into account fungal growth, dissolved oxygen, glucose consumption, starch hydrolysis, glucoamylase activity, volumetric oxygen transfer coefficient and apparent viscosity. The fungal growth has been estimated using on-line measurements of CO2 evolution during fermentation.

Estimation of fungal growth in complex, heterogeneous culture

Abstract Very often, fungal fermentation processes are carried out on complex heterogeneous media, such as whole wheat flour, which are constituted of various soluble and insoluble solid particles. The measurement of the course of fungal growth during such fermentations, which are conducted in either submerged or solid state, is hindered by the presence of insoluble solid particles. The knowledge of the profile of biomass growth throughout any fermentation process constitutes an essential parameter in the estimation of kinetic variables and, subsequently, scale-up of the process. In this study, a method for the determination of fungal concentration during fermentation on whole wheat flour has been developed. The technique is based on on-line measurements of CO 2 evolution during fermentation of Aspergillus awamori on whole wheat flour. Initial values for yield ( Y X/CO ) and maintenance ( m CO ) coefficients were calculated from fermentations on synthetic media. Variations in impeller speed (350–550xa0rpm) and aeration rate (5–7xa0l/min) during fermentation caused significant effects on fungal growth.

The application of a generic feedstock from wheat for microbial fermentations.

The feasibility of a generic fermentation feedstock produced from wheat flour has been confirmed in several fermentations of yeasts, bacterium, and filamentous fungus for the production of commodity chemicals. Saccharomyces cerevisiae was incubated for the observation of yeast growth and ethanol production, Pichia farinosa for glycerol production, Monascus purpureus for fungal growth and pigment production, and Lactobacillus bulgaricus for bacteria growth and lactic acid production. The results confirmed that the feedstock contained no inhibitory components to the strains tested. Similar or higher metabolite yields were obtained in comparison with other studies carried in commonly used media.

Enzymatic hydrolysis of polysaccharides: Hydrolysis of starch by an enzyme complex from fermentation by Aspergillus awamori

In this work an amylolitic enzyme complex—obtained from fermentation of whole wheat flour by Aspergillus awamori—was used for starch hydrolysis in batch and continuous (hollow fibre membrane bioreactor) systems. In the batch system a model was applied to describe glucose production. The continuous enzyme membrane system worked more efficiently compared to the batch system at low substrate concentrations.