Interfacial interactions with microorganisms: Application in fermentation technology

The implications of interfacial phenomena in fermentation processes are outlined, pointing out the relevance of recent data to basic aspects of bioadhesion. The surface properties of brewing yeasts (chemical composition, zeta potential, hydrophobicity) are related to the type of fermentation; cell flocculation involves both non specific and specific interactions. Adhesion of cells to surfaces, the first step of biofilm formation, is determined by the interplay of electrostatic and hydrophobic interactions, the former being easier to act upon by the addition of chemicals. Flotation, which may be used in separation operations, relies mainly on cell hydrophobicity. The metabolic activity of microbial cells immobilized by adhesion or flocculation is strongly influenced by mass transfer limitations, shear forces and modification of the composition of the solution surrounding the cells. This may create situations where the state of aggregation, determined by the agitation, affects the cell growth and the cell surface properties, whilst the aggregation is usually expected to be the consequence of surface properties. Such indirect effects must be taken into consideration before invoking any direct physico‐chemical influence of a surface on the activity of adhering microorganisms.

Key words:

• Fermentation
• interface
• surface properties
• flocculation
• adhesion
• flotation
• metabolic activity
• biofilms