Microbial Polysaccharides: Xanthan, Gellan, and Curdlan in Foods

Ever wondered how your salad dressing stays perfectly blended, how a vegan jelly holds its shape, or how that low-fat yogurt still feels creamy and rich? The secret often lies in tiny, invisible ingredients that work tirelessly behind the scenes. We’re not talking about artificial chemicals, but rather amazing natural products created by microorganisms. These are microbial polysaccharides, and they are some of the most powerful tools in modern food science for creating the textures we love. While many familiar food thickeners come from plants (like cornstarch) or seaweed (like carrageenan), a special class of “gums” is produced through microbial fermentation. Let’s explore three of the most important ones: xanthan gum, gellan gum, and curdlan.

What are microbial polysaccharides? 🔗

At its simplest, a polysaccharide is a long chain of sugar molecules linked together. “Microbial” simply means these complex chains are produced by tiny living organisms, specifically bacteria. In nature, bacteria produce these gummy substances-called exopolysaccharides-to protect themselves, stick to surfaces, or store food. Scientists in the mid-20th century discovered that these natural polymers had incredibly useful properties for managing water in food products.

In a food production facility, this process is harnessed on a large scale. Specific strains of bacteria are grown in a large vat (a fermenter) and “fed” a sugar-rich liquid, often derived from corn, soy, or wheat. As the bacteria consume the sugar, they excrete their specific polysaccharide. After the fermentation is complete, the gum is separated from the bacteria and the liquid, purified, dried, and milled into a fine powder. This powder is what ends up in our food, where it acts as a hydrocolloid-a substance that forms a gel or thickens a solution when mixed with water. Though they all manage water, our three examples do it in very different and unique ways.

Xanthan gum: The pseudoplastic champion 🔗

If you read ingredient labels, you’ve almost certainly seen xanthan gum. It is perhaps the most common microbial polysaccharide, discovered in the 1950s by researchers at the USDA. It is produced by the bacterium Xanthomonas campestris, which, funnily enough, is the same microbe responsible for causing black rot on broccoli and cauliflower. But the gum it produces is not only harmless, it’s a food-industry superstar.

The magic of shear-thinning 🔗

Xanthan gum’s most famous property is its pseudoplasticity, or “shear-thinning” behavior. This sounds complicated, but you experience it every day. Imagine a bottle of creamy salad dressing. It looks thick and stable in the bottle, with the oil, water, and spices perfectly suspended. That’s xanthan gum at rest, creating a high-viscosity network. But when you shake the bottle or pour the dressing (applying “shear”), it suddenly flows like a much thinner liquid. The moment it lands on your salad (the shear is removed), it thickens up again, clinging to the lettuce instead of pooling at the bottom of the bowl. This is the pseudoplastic magic. Ketchup, fruit syrups, and sauces use xanthan gum for this exact reason: thick when still, but easy to pour.

The ultimate stabilizer 🔗

Beyond its flow, xanthan gum is an exceptional stabilizer. It’s incredibly stable over a wide range of temperatures and pH levels. This means it works just as well in a highly acidic vinaigrette as it does in a neutral-pH dairy product. Its most valuable trait for many products is its excellent freeze-thaw stability. In conventional foods, freezing and thawing can cause water to separate out (a process called syneresis), forming ice crystals that ruin the texture. Xanthan gum holds onto that water tightly, preventing ice crystal growth and ensuring that a frozen sauce or ice cream thaws into the same smooth, creamy product it was before freezing. It’s also a key ingredient in gluten-free baking, where it mimics the elastic, gas-trapping structure of gluten, giving bread and cakes the volume and texture they would otherwise lack.

Gellan gum: The precision gel architect 🔗

Where xanthan gum is known for thickening and stabilizing, gellan gum is a master of gelling. Discovered in 1978 from the bacterium Sphingomonas paucimobilis (which was found in a water lily pond), gellan gum is powerful, creating firm gels at incredibly low concentrations. Its true genius, however, lies in its versatility. Food producers don’t just use “gellan gum”; they use two different types to create a huge range of textures.

High-acyl vs. low-acyl gellan 🔗

The two forms of gellan gum offer a study in contrasts. High-acyl (HA) gellan gum, which retains a natural chemical group called an acyl, produces soft, elastic, and flexible gels. Think of the texture of a soft set pudding or a firm custard. In contrast, low-acyl (LA) gellan gum, where that group has been removed, forms gels that are firm, brittle, and often strikingly clear (PDF). Think of a classic Jell-O style dessert, but with a plant-based origin.

The real power comes when food scientists blend the two. By precisely combining HA and LA gellan, they can dial in the exact texture they want-from soft and springy to firm and sliceable. This makes it a go-to replacement for gelatin in vegetarian and vegan products, like gummy candies, jellies, and desserts.

The ‘fluid gel’ for suspending 🔗

Perhaps gellan’s most clever application is in beverages, where it creates something called a “fluid gel.” Have you ever wondered how in chocolate almond milk, the cocoa powder stays perfectly mixed and doesn’t settle into a sludge at the bottom? Or how the extra calcium in fortified orange juice stays suspended? That’s often gellan gum. At a very low concentration, it forms an extremely weak, invisible gel network throughout the liquid. This network is just strong enough to hold tiny particles (like calcium, protein, or cocoa) in suspension, but so delicate that it breaks instantly when you pour or drink it, so the beverage still feels like a normal, non-thick liquid. It’s a high-tech solution to the age-old problem of settling.

Curdlan: The unique heat-set texturizer 🔗

Our third microbe, Agrobacterium biobar, produces curdlan, a polysaccharide with a truly unique and useful property that sets it apart from all others. While most gelling agents like gellan or gelatin form a gel upon *cooling*, curdlan forms its strongest gel when it’s *heated*. This makes it a thermo-irreversible gelling agent, and it opens up a whole new world of textural possibilities.

A gel that ‘cooks’ into place 🔗

Curdlan’s behavior is fascinating. When you mix curdlan powder with water and heat it, it first forms a weak, reversible gel at around 55-65°C. But if you keep heating it past 80°C (like during a cooking or pasteurization process), it undergoes a transformation, setting into a very firm, stable gel. The “irreversible” part means that, unlike gelatin, this gel will not melt again, even if you reheat it. It’s much like cooking an egg: once the proteins are set, they stay set.

Improving bite and stability in cooked foods 🔗

This heat-set property is invaluable in processed foods that are cooked before being eaten. Curdlan is a popular ingredient in meat and fish products like sausages, hot dogs, and fish cakes. When the product is cooked during manufacturing, the curdlan activates, forming its strong gel network. This network helps improve the “bite” and firmness, making the texture more resilient and snappy. It also does a fantastic job of binding water, which means a juicier final product that doesn’t shrink or dry out as much during cooking.

This water-binding and textural magic also makes curdlan a powerful tool in creating low-fat foods. When fat is removed from a product like a sauce or a meat patty, the creamy mouthfeel and satisfying texture often go with it. Curdlan’s stable gel network can be used to mimic the “body” and richness of fat, creating a more palatable and satisfying low-fat alternative. It’s also used to improve the texture of noodles, helping them stay firm and elastic even after boiling.

From the pourable salad dressing in your fridge to the springy vegan gummies in your pantry, these microbial polysaccharides are the hidden architects of food texture. Xanthan provides the smooth, stable flow; gellan builds gels with precision; and curdlan sets with heat to create bite and resilience. They are powerful reminders that sometimes, the smallest organisms can make the biggest impact on our daily lives.

What do you think? Now that you know about these ingredients, have you spotted xanthan or gellan gum on an ingredient label recently? Does understanding their function change how you think about processed foods?

References

1. https://www.sciencedirect.com/topics/food-science/xanthan-gum
2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3766698/
3. https://www.fao.org/fileadmin/user_upload/codex/docs/JECFA/Evaluation_ additives/additive-231-JECFA_57-F.pdf
4. https://foodadditives.net/thickeners/gellan-gum/
5. https://www.efsa.europa.eu/en/efsajournal/pub/2311