Plant pathogens turn into food additives

The bacteria Xanthomonas campestris is responsible for a variety of plant disease and for the consistency of salad dressings. Composed by Gorm Palmgren from and

We normally try to avoid pathogens – from our own bodies but also from our crops. But sometimes plant pathogens can actually come in handy and the food industry knows that very well. Many well known food additives have their origin in these pests and allthough that might give them a natural label it can also be perceived as quite disgusting. Nobody would like to eat bacterial slime or bugs, so the industry handily calls it E415 or E904 instead. There is nothing unnatural about the thick, creamy consistency of ready-to-eat salad dressings and sauces. But you might be surprised to know, that the good result is garantied by slime from the bacteria Xanthomonas campestris that causes rot and several other diseases on cabbage, broccoli and many more crops.

The plant pathogen produces a viscous slime known as xanthan gum for its own protection. It is a natural product consisting of three kinds of sugar molecules put together in long, branched chains. It is a very effective thickening agent and as little as 5 grams of xanthan gum can turn 1 liter of water into a sauce with the same consistency as ketchup. The food industry takes advantage of this to change the viscosity of salad dressings and sauces so they are more easy to dispense and also stick better to vegetables and meats. A special characteristic of xanthan gum is that mechanical forces temporarily make it loose its thickening properties. This means that the sauce is easy to pour when you have just shaken the bottle, but almost immediately regains its original consistency on the plate.

The insect lac scale or Kerria lacca feeds on plants and is used for production of shellac that gives a glossy and shiny surface to candy. From

Most people with a garden will know the scale insects that rest immobilised on leaves, well hidden under a glossy shell. It might almost look like a piece of candy and that is no coincidence, because one of these bugs, Kerria lacca, is an important player in the candy industry. Females cluster on plant parts, stick their mouthparts into the phloem and suck out the sugary sap. The sap, however, contains far too much sugar for a well balanced meal, so excess sugar is secreted as a resin-like substance known as shellac.

In India alone, almost 3 million poor people make a living of harvesting shellac from the bugs, that can almost cover a branch. They beat the branches with a wooden hammer so the shells break and fall to the ground, or they harvest whole branches and take them to a small, local factory where the shells are ground to a fine powder. It is then heated so as to melt the resin and impurities are filtered away. It takes around 250.000 lac scales to make 1 kg of shellac, which is a pure and allergy-friendly natural product. Besides from making candy shine, shellac is used to protect apples and oranges and if you want a fine piece of furniture to look really beautiful, there is no better lacquer than shellac.

Cellulose is an excellent filler that can substitute fat in many foods. Composed by Gorm Palmgren from and

Not only plant pathogens but also specific plant parts don’t sound particular appetising. Sawdust doesn’t present itself as a delicacy but it can actually make food both more delicious and more healthy. Cellulose, the main component of wood, consists of pure fibers and they are increasingly used as a filler in many foods. The fibres contributes with a light and fluffy consistency to ice cream, and they retain water so a liver paté remains juicy even though it has been fat reduced. Cellulose is also added to white bread and morning cereals to increase the fiber content. Normally 1-4% of cellulose is added to foodstuffs and it is regarded as being so harmless that it is even allowed in organic foods.

Food additives from pathogens and dubious parts of plants

Additive Origin Natural function Food function
Xanthan gum Rot bacteria Xanthamonas Protective slime Thickener in sauces and dressings
Shellac Scale insect Kerria lacca Protective shield Shiny and glossy surface of candy
Cellulose Wood and sawdust Strength and support for cells Fluffy consistency, fat reducer, adds fiber


By Gorm Palmgren, science writer, PhD,