Organic acid production
Organic acids are used in the food and beverage industry as acidulants, preservatives and buffering agents. The production organism and conditions vary with the acid. Lactic acid is produced by lactic acid bacteria under anaerobic or microaerophilic conditions, in a fermentation in which the acid formed is neutralised with a base. Citric acid is obtained by submerged fermentation with Aspergillus niger at low pH and with a high oxygen requirement. Gluconic acid is produced by the oxidation of glucose with Aspergillus niger or Gluconobacter.
Application-specific process requirements
pH control and neutralisation
In lactic acid fermentation, the accumulating acid lowers pH and slows growth and product formation (product inhibition). pH is held at set point with sodium hydroxide, ammonium hydroxide or calcium hydroxide. The neutralising agent determines the salt form of the product and the purification load; acidifying calcium lactate with sulphuric acid produces gypsum (calcium sulphate) as a by-product.
Fungal processes at low pH
Citric acid fermentation runs at around pH 2. Low pH reduces the risk of contamination; the compatibility of product-contact surfaces and sensors with this condition is verified within the project. Because trace metals in the medium, manganese in particular, affect yield, medium preparation and material selection are evaluated together. Gluconic acid production with the same organism, by contrast, runs at pH 6.0–6.5 with neutralisation by sodium hydroxide; the product is obtained as sodium gluconate.
Oxygen transfer and morphology
Citric and gluconic acid production require high oxygen transfer. Pellet or dispersed mycelial morphology changes viscosity and therefore the volumetric oxygen transfer coefficient (kLa). Dissolved oxygen is held by cascade control through agitation speed and mass-flow-controlled air flow. Even a brief drop in dissolved oxygen can permanently reduce the rate of citric acid formation; continuity of air supply and agitation is therefore addressed in the design.
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 |
| TLM120 | Pilot-scale systems | 20 L seed reactor + 100 L pilot reactor | Automated SIP | Skid-mounted | Shared phase, 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 target acid, organism, carbon source, neutralising agent and annual production target is sufficient for an initial assessment.