Sophorolipid production by yeasts: a critical review of the literature and suggestions for future research.

Sophorolipids are well-known biosurfactants produced by yeasts, having potential applications ranging from nanomaterials, medicine, and cosmetics to large-volume applications such as cleaning and soil remediation. Because of their environmentally friendly nature, they attained much interest during the past decades as a sustainable and ecological alternative to petroleum-derived surfactants. Stronger yet, research activities and scientific publications on the topic are ever increasing. However, often these studies lack proper producer strain identification and detailed structural product characterization. Flaws regarding strain identity can have huge consequences when moving to valorization and moreover tend to persist quite long in scientific literature. Furthermore, too often sophorolipid production is proposed where other biosurfactant structures cannot be ruled out based on the chemical analysis. Finally, absolute quantitative yield determination frequently occurs with variable product purity and without proper calibration standards. This review aims to highlight and discuss these discrepancies and proposes some guidelines for good practice in future sophorolipid research.