Foams are a widely used shape in which cosmetics and pharmaceuticals are applied due to their good spreading ability and their lack of stickiness. Nowadays, cosmetic manufacturers are eager to provide their products in foam form, because consumers consider foamlike cleaning products are of higher quality with better usability.

Surfactants, as the main component of washing cosmetics, achieve foaming by quickly and effectively reducing the surface tension. Compared with synthetic surfactants, natural biological substitutes (biosurfactants) have attracted more and more attention in body care and bath cosmetic fields due to their low toxicity and inherent biodegradability. Rhamnolipid (RHA) is one of these biosurfactants which is produced by bacteria such as Pseudomonas aeruginosa. RHA has a considerably lower standard Gibbs free energy of adsorption and micellization, therefore RHA can form micelles much more easily than synthetic surfactants. However, surfactants are often not enough to ensure the stability of the foam, and other components like proteins are necessary to improve the stability. Though many studies on the mixture of protein and biosurfactants have been conducted, the synergistic or antagonistic effect of protein addition on the foaming properties of biosurfactants still needs to be solved. Recently Wang and coworkers have studied the interaction between soybean protein (SP) and RHA proposing a possible correlation between surface behavior and actual foaming properties.