Fermentation produces a dilute, extremely viscous broth that is maybe 1–3 % polymer by weight. Turning that broth into the white powder on your shelf takes a series of separation and finishing steps, and those steps do more to determine the grade you receive than the fermentation itself.
Step 1: Killing the cells
Before anything is separated, the broth is pasteurised. This does two things: it stops the fermentation at a defined point, and it kills the producing organism.
Regulators care about this step. The EFSA re-evaluation of E 418 noted that the specifications should better define the absence of viable cells of the microbial source. In practice, buyers should expect a microbial specification and, where relevant, a statement on the absence of viable producer cells.
Step 2: Separating polymer from broth
The polymer is recovered by precipitation. Two routes dominate:
- Alcohol precipitation. The broth is mixed with a water-miscible alcohol — isopropyl alcohol is the classic choice — which collapses the polymer out of solution as a fibrous precipitate. This gives the cleanest product and is the most common route for food and pharmaceutical grades.
- Salt precipitation. Adding a salt solution can also drive the polymer out. It avoids large alcohol volumes but demands tighter control over ionic content in the finished material.
The precipitated fibre is then dewatered, pressed and dried. Alcohol recovery and energy use at this stage are a major part of the cost and the environmental footprint of the ingredient.
Step 3: Deacylation — where HA becomes LA
Native gellan gum carries acyl groups (a glyceryl group and an acetyl group) on the polymer backbone. This high acyl (HA) form gives soft, elastic, transparent gels.
To make low acyl (LA) gellan gum, the polymer is treated with alkali under controlled temperature and time. The alkali hydrolyses the acyl groups away. The result is a polymer that forms firm, brittle gels and requires cations to set.
Two consequences are worth remembering:
- Deacylation is not all-or-nothing. Alkali treatment can be run to different degrees, so "LA" covers a family of materials, not a single fixed structure.
- Alkaline conditions also reduce molecular weight through chain cleavage. This is why LA grades typically show lower viscosity than HA grades at the same concentration — a difference that is structural, not a manufacturing defect.
This single step is why HA and LA are best understood as two ends of a spectrum rather than two unrelated products.
Step 4: Drying
Two drying routes are common:
- Drum drying — economical, gives a dense flake or coarse powder.
- Spray drying — gives a finer, more uniform powder and is the route to agglomerated "instant" grades that disperse without lumping.
Drying also sets the moisture content and loss on drying on the specification. Over-drying wastes energy; under-drying shortens shelf life and encourages caking.
Step 5: Milling and mesh
Finally the dried polymer is milled and screened to a target particle size. Grind size drives how fast the powder wets out and hydrates, how much dust it generates and how easily it lumps if added badly.
A useful rule of thumb: finer powder hydrates faster but is harder to disperse; coarser powder disperses more easily but hydrates more slowly. Nothing can be done at the mixing stage to fully compensate for the wrong grind.
The residues that come along for the ride
Downstream processing does not produce a pure polysaccharide. Typical finished material also contains:
| Fraction | Comment |
|---|---|
| Moisture | Usually a few percent, reported as loss on drying |
| Proteinaceous material | Reported as nitrogen content, commonly up to about 3 % |
| Polyhydroxybutyrate (PHB) | A bacterial storage polyester that can reach a substantial fraction of the powder |
| Ash and residual salts | Carried through from the broth and the precipitation step |
| Residual enzymatic activity | Enzymes from the producing organism that survive processing |
That last row deserves attention. Residual enzymatic activity can continue to act slowly on the polymer during storage, which is one route to the "gel strength dropped after six months on the shelf" complaint. A supplier who monitors it is a supplier who can hold performance over time.
What to ask your supplier
If you are qualifying a new source of gellan gum, these questions separate a real process description from a sales sheet:
- Which recovery route do you use, and do you monitor residual isopropanol?
- How do you control the degree of deacylation, and is it measured or only assumed?
- Do you monitor molecular weight, and what is your typical range?
- What is your specification for PHB, nitrogen and residual enzymatic activity?
- Can you supply a typical particle size distribution rather than a single mesh number?
For specification data, samples and formulation support, contact Cinogel.
Part of the E418.org gellan gum knowledge base.