A review of sophorolipid production from alternative feedstocks for the development of a localized selection strategy

The replacement of traditional petroleum-based surfactants with renewable biosurfactants is a key part of the transition towards a circular economy. Sophorolipids are the most commercially adopted biosurfactant due to the existence of high productivity fermentation process, excellent surface and interfacial tension properties and because the main producer organism Starmerella bombicola is non-pathogenic/non-GMO. However, the current large-scale production of sophorolipids still utilizes purified substrates such as glucose and oleic acid. This is a major reason their price is an order of magnitude higher than traditional surfactants, severely limiting their commercial adoption. Hence, implementation of sophorolipid production from alternative biomass byproducts and wastes is crucial. This review illustrates the potential performance of alternative feedstocks as sources of sugars, fatty acids and nitrogen for sophorolipid production. Important studies where alternative feedstocks outperformed purified substrates under the same conditions, as well as high overall production of sophorolipid using sophisticated fermentation schemes are highlighted. Promising performance such as productivities of up to 2.4 g/L/h currently exist with processes based on alternative feedstocks. Important knowledge gaps within the literature are also identified, such as the need to combine alternative feedstocks to eliminate the use of purified substrates. Future improvement of productivity on alternative feedstocks could be achieved via implementation of sophisticated fermentation schemes to either improve cell titer during growth or to improve SL production itself, such as in-situ separation of sophorolipids. Selection criteria were produced using key performance factors identified from the literature, together with other factors such as available quantity, price and logistics as well as the potential for integrated biorefining. These selection criteria were then applied to the UK as a case study. In the future, the framework developed could be applied to feedstock assessment and selection for localized sophorolipid production in various locations around the world.