Microbial polysaccharides and biopolymers
Xanthan gum (Xanthomonas campestris), pullulan (Aureobasidium pullulans) and other microbial exopolysaccharides are used as thickeners and stabilisers in food, cosmetic and industrial applications. In these fermentations the product is secreted outside the cell, and as it accumulates the viscosity of the medium rises; the medium becomes a shear-thinning (pseudoplastic) fluid. Polyhydroxyalkanoates (PHA) are biodegradable polyesters that accumulate inside the cell; accumulation is mostly triggered by nutrient limitation.
Application-specific process requirements
Rheology and agitation
In pseudoplastic fluids, shear rate is high around the agitator and low near the vessel wall. Apparent viscosity therefore rises with distance from the agitator; stagnant volumes and oxygen gradients can form in distant regions. We select agitator type, diameter, number of stages and motor power for the highest viscosity the process will reach.
Oxygen transfer
As viscosity rises, the volumetric oxygen transfer coefficient (kLa) falls; in xanthan fermentation, oxygen transfer is usually the limiting factor of the process. Dissolved oxygen is held by cascade control through agitation speed and air flow; adding vessel pressure to the cascade is evaluated within the project. Where stagnant regions form, dissolved oxygen measured at a single point may not represent the whole volume; the DO sensor position is therefore set in the design.
In-line viscosity measurement
In polysaccharide processes, viscosity rises with product concentration and molecular weight; it is therefore monitored as an indirect indicator of product formation. In a pseudoplastic fluid the reading is the apparent viscosity at the sensor’s own shear rate; its relation to product concentration is established with laboratory rheometer measurements. An in-line process viscometer is added to Talamus systems as a PAT option. We have been installing and calibrating process viscometers in food, chemical and biotechnology plants since 2011.
PHA and nutrient limitation
In PHA production, biomass is first grown in a balanced medium. Nitrogen or phosphorus is then limited and the excess carbon is directed to polymer accumulation. The phase transition is defined in the feed profile.
Production methods used
Talamus models for this application
| Model | Scale | Working volume | Sterilisation | Delivery | Control structure |
|---|---|---|---|---|---|
| TLM Lab | Laboratory systems | Laboratory scale; vessel volume and number of parallel reactors per configuration | Autoclave | Benchtop | Shared loop and data structure |
| TLM500 | Pilot-scale systems | 500 L working volume (600 L total) | Automated SIP | Skid-mounted | Shared phase, loop and data structure |
| TLM Industrial | Industrial systems | 1,000 L – 30,000 L working volume | SIP/CIP, per project | Line engineered per project | Shared phase, loop and data structure |
Technical consultation request
Information on the product, organism, target product concentration and expected maximum viscosity is sufficient for an initial assessment.