Starch is the most commonly used hydrocolloid thickener, used in both native and modified forms, according to a review of thickening and gelling agents in the Journal of Food Science and Technology. Native starch does not dissolve in cold water. As water is heated it penetrates the granules, they swell, and close to boiling the paste thickens.
That works in a kitchen. In a factory, the paste may then have to survive pumping, acidic ingredients, intense heat treatment, freezing and weeks on a shelf. A 2023 review of starch modification in Polymers sums up the problem: native starches have restricted applications, and modification is carried out to strengthen their useful characteristics and remove their limitations.
What each modification changes
The Polymers review sets out what each main type of modification does to starch.
| Modification | What it changes |
|---|---|
| Cross-linking | Forms bridges within and between starch molecules, making granules more stable against swelling, high temperature, high shear and acidic conditions |
| Esterification, for example acetylation | Lowers gelatinisation temperature and retrogradation, reduces the tendency to gel and increases paste clarity |
| Etherification, for example hydroxypropylation | Clearer pastes, higher viscosity, less syneresis and better freeze-thaw stability |
| Oxidation | Low viscosity, high clarity and stability at low temperature |
| Acid hydrolysis, or acid thinning | Low paste viscosity with high gel strength |
| Pregelatinisation, a physical treatment | Starch is cooked in water and then drum or spray dried, giving a starch that is cold water soluble with enhanced viscosity |
The review notes food uses for several of these: cross-linked starches as viscosifiers and texturisers in dairy products, esterified starches as emulsion stabilisers in refrigerated and frozen foods, oxidised starches in batters and coatings and as binders in confectionery, and acid-thinned starches as gelling agents in gums and processed cheese and as fat replacers.
Cross-linking is the most frequently applied method, according to the review. In practice a single food starch is often modified in more than one way, for example cross-linked for process tolerance and stabilised for shelf life, so the specification is worth reading closely.
Reading the symptoms
- Thins out during pumping, mixing or cooking. Granules are breaking down under shear or heat, the problem cross-linking addresses.
- Thins out in an acidic product. Also a job for cross-linking.
- Weeps water or sets up in the chiller. Retrogradation, which esterified and etherified starches are made to resist.
- Leaks water after freezing and thawing. Poor freeze-thaw stability, addressed by etherification.
- Needs to thicken without cooking. A pregelatinised starch.
- Needs to set firm, as in a gum confection. An acid-thinned starch.
Not all modification is chemical
The Polymers review also covers physical methods, which it describes as easy, cost-effective and largely environmentally friendly. Thermal treatments include pregelatinisation, extrusion, heat-moisture treatment and annealing, while non-thermal methods include ultra-high pressure. Where the ingredient declaration matters to a product's positioning, physically modified starches deserve a place in the trial.
Check the label and the permitted use. Chemically modified starches are regulated as food additives in most markets, and how they must be declared, and in which products they may be used, is set by the applicable regulations. Confirm the current requirements for your product category before finalising a specification.