Sophorolipid

What is a sophorolipid?

A sophorolipid is a biosurfactant in the glycolipid family. It is produced by a small group of yeasts, the best known and most productive being Starmerella bombicola, formerly called Candida bombicola. Sophorolipids are among the most commercially developed biosurfactants, because the producing yeast makes them in large quantities on inexpensive feedstocks.

Structure

A sophorolipid molecule has two parts:

• The head group is sophorose, a sugar made of two glucose units. Its many hydroxyl groups make it water-attracting.
• The tail is a long-chain hydroxylated fatty acid, most commonly with 16 or 18 carbons, attached to the sugar. It is water-repelling.

The yeast does not make one single molecule but a family of closely related ones, and they fall into two main forms:

• Acidic sophorolipids have an open structure with a free carboxylic acid group at the end of the fatty acid. They are more water-soluble and generally better at producing foam.
• Lactonic sophorolipids have the fatty acid looped back and bonded to the sugar, closing the molecule into a ring. They are less water-soluble and generally more effective at lowering surface tension.

The sugar can also carry acetyl groups, and the fatty acid chains vary in length and saturation. The balance of these variants, which depends on the strain, the feedstock and the fermentation conditions, determines how a particular sophorolipid product behaves.

How sophorolipids are produced

Sophorolipids are made by fermentation. The yeast is grown on a sugar such as glucose, usually together with a plant oil or fatty acid, and secretes sophorolipids into the broth. Because the lactonic form is poorly soluble, it can separate as a dense oily phase, which simplifies recovery. The product is then purified and, where needed, adjusted toward the acidic or lactonic form. Sophorolipid yields are among the highest reported for any biosurfactant, which is the main reason sophorolipids reached commercial scale early.

Properties and uses

Like other surfactants, sophorolipids gather at interfaces, lower surface and interfacial tension, and form micelles. Their sugar head group means they behave largely like nonionic surfactants, and they are generally described as low-foaming and readily biodegradable. They are used as wetting agents and co-surfactants in cleaning products, in personal care, in agricultural formulations, and in oilfield and mineral processing applications.

Sophorolipids and rhamnolipids

The two best-known glycolipid biosurfactants differ in the organism that makes them and in their structure.

	Sophorolipid	Rhamnolipid
Producing organism	Yeast, mainly Starmerella bombicola	Bacteria, mainly Pseudomonas species
Sugar head group	Sophorose (two glucose units)	One or two rhamnose units
Main forms	Acidic and lactonic	Mono- and di-rhamnolipids
Frequently cited strength	Emulsification and wetting	Cleaning and emulsification

Sophorolipids at Locus

Locus produces sophorolipid-based glycolipid biosurfactants by fermentation at commercial scale. Its Amphi ingredient line, marketed to formulators as a glycolipid co-surfactant, is built on sophorolipids.

Frequently asked questions