High acyl and low acyl gellan gum behave so differently that they almost seem like different ingredients. The reason is a small chemical detail: a pair of acyl groups sitting on the polymer backbone.
What "acyl" means here
In the high acyl (native) form, some of the glucose residues in the repeating unit carry two substituents:
- a glyceryl group
- an acetyl group
Both are attached to the same sugar residue through ester linkages — the glyceryl group at the C-2 hydroxyl and the acetyl group at C-6, in the accepted structure. They are not part of the backbone; they hang off it.
The word "acyl content" simply means how much of this substitution is present. High acyl (HA) material retains it. Low acyl (LA) material has had it chemically removed.
Why two small groups change everything
Gel formation in gellan gum happens in two stages: the chains first coil into helices, then those helices aggregate into a three-dimensional network.
The acyl groups interfere with the second stage. They are bulky, and they physically get in the way of helix-to-helix association. The consequences are dramatic:
| Property | High acyl (HA) | Low acyl (LA) |
|---|---|---|
| Gel texture | Soft, elastic, cohesive | Firm, brittle, short |
| Appearance | Usually more transparent | Can be opaque or hazy depending on ions |
| Thermal behaviour | Gels melt at relatively low temperature — thermally reversible | Gels are far more heat-stable |
| Ions needed | Gels without added cations | Needs cations (calcium, magnesium, potassium, sodium) to set |
| Typical use | Soft jellies, elastic textures, dairy-style gels | Suspension, firm gels, structured liquids |
Neither is better. The choice is about the texture and the process temperature your product can tolerate.
"Low acyl" is not a single thing
This is where product names mislead. Deacylation is done with alkali under controlled temperature and time. The treatment can be run to different degrees, so material sold as "low acyl" spans a range:
- Trace acyl content, fully deacylated material.
- Partially deacylated material with measurable residual acyl groups.
A partially deacylated powder can sit between the two classic textures — softer than a typical LA grade, firmer than an HA grade. If your product was developed around one supplier's LA grade and you switch to another whose deacylation is slightly different, the gel can shift noticeably. That is a real and often misdiagnosed cause of "the same grade does not work any more".
How acyl content is measured
Several methods are used, in rough order of how often you will see them on a specification:
- ¹H-NMR — the most direct structural measurement. It identifies and quantifies the glyceryl and acetyl signals.
- HPLC after hydrolysis — the acyl groups are liberated and quantified as glyceric acid and acetic acid.
- Saponification or titration — cheaper, wet-chemical routes giving total acyl content.
- Infrared spectroscopy — useful as a fingerprint or a comparative check rather than an absolute number.
Most commercial spec sheets do not report acyl content at all. They report "high acyl" or "low acyl" and leave it there. If you are having texture drift problems that survive every other explanation, asking for an acyl content figure is a reasonable next step.
Practical rules of thumb
- Do not infer acyl content from gel strength. Two grades can have similar gel strength by different combinations of acyl content and molecular weight.
- Do not assume a supplier's LA equals another supplier's LA. Ask what deacylation conditions they use and whether the degree is measured.
- Blending HA and LA is a legitimate tool. Mixing the two lets you tune texture between the elastic and brittle extremes without changing total gum level. This is common practice, and it is worth developing as its own formulation variable.
- Ions still matter for LA. Acyl content determines how the network forms; ions determine how strong it becomes.
Where to look next
If you are choosing between the two, the decision usually comes down to three questions: what texture do you need, what temperature does your process reach, and does the product need to re-melt later? Answer those three and the choice is usually obvious.
For both HA and LA grades with full technical data, see Cinogel.
Part of the E418.org gellan gum knowledge base. See also: what is high acyl gellan gum, and what is low acyl gellan gum.