# Biosurfactants Glycolipid structure and interfacial activity, why critical micelle concentration is the meaningful potency measure, how sophorolipid lactone-versus-acid form changes function, and the foaming and emulsion problems that define the process. You are making a foaming agent inside an aerated, stirred tank — the process fights its own product. Source: https://en.bioecon.ru/docs/biochem-industrial/specialty-fine-chem/biosurfactants/ Updated: 2026-08-25 Biosurfactants are amphiphilic molecules made by microorganisms — most commercially, glycolipids: a sugar head group joined to one or more fatty acid tails. Rhamnolipids carry rhamnose, sophorolipids carry the disaccharide sophorose, and mannosylerythritol lipids carry a mannose–erythritol head. ## What surface activity actually is A surfactant lowers interfacial tension because its two ends want different environments. At an oil–water or air–water interface the molecule adsorbs with its tail out of the water and its head in it, and each adsorbed molecule replaces part of the high-energy interface with something lower in energy. Above a threshold concentration the interface saturates and additional molecules instead aggregate into micelles in the bulk. That threshold — the **critical micelle concentration** — is the meaningful potency figure, because surface tension stops falling above it. A surfactant with a low CMC does the same job at a lower dose. Glycolipid biosurfactants generally have markedly lower CMCs than common petrochemical surfactants. The structural reason is that they are bulkier and more strongly amphiphilic: a disaccharide head hydrogen-bonds extensively with water while a branched or hydroxylated fatty tail is strongly excluded from it, so aggregation is favoured at lower concentration. Lower CMC at higher unit price is the trade the category actually offers, and comparing prices per kilogram rather than per unit of performance gets it wrong. ## Structure decides function, visibly Sophorolipids are the clearest illustration. They are secreted as a mixture of two forms: an **acidic** form with a free carboxyl on the fatty acid tail, and a **lactonic** form in which that carboxyl has esterified back onto the sugar, closing a ring. The two behave differently. The open acidic form is more water-soluble, foams better and is the better detergent. The closed lactonic form is more hydrophobic, packs more tightly at interfaces, and has markedly stronger antimicrobial activity — its rigid ring inserts into membranes more effectively. The ratio is controlled by fermentation conditions and by post-processing, so a single organism supplies either a cleaning surfactant or an antimicrobial depending on how the product is finished. ## The process fights the product Glycolipid production is aerobic, so the fermenter is sparged and agitated. The product is a surfactant. **The result is severe foaming**, which carries broth out of the vessel, fouls exhaust filters and limits how hard the tank can be aerated — which in turn limits oxygen transfer and therefore productivity. Chemical antifoams work against the product's own function and contaminate it. Mechanical foam breakers, reduced working volume and foam-fractionation designs that harvest the product *from* the foam are the real answers, and the last of these turns the problem into a separation step. Recovery is the second difficulty and has the same root. A surfactant emulsifies the broth it sits in, so ordinary liquid–liquid extraction gives stable emulsions that will not break. Acid precipitation, solvent extraction under carefully chosen conditions, or foam fractionation are used instead. Where the substrate is a plant oil rather than sugar — common for sophorolipids — the fermenter contains three phases, and the surfactant being produced emulsifies its own feedstock, which helps uptake and complicates everything downstream. Biodegradability is genuinely favourable, being glycolipids that ordinary environmental organisms can cleave, but it should be stated as measured under a defined test rather than assumed from origin.