Penicillium digitatum is the causal agent for citrus green mold which generates 90% of post-harvest losses in Mediterranean countries. The use of a green seaweed extract to fight this fungal pathogen could represent an ecofriendly alternative to chemical fungicides. We propose to formulate an aqueous extract from Ulva lactuca (8.3%) in an emulsion for the preventive treatment of oranges. New biobased emulsifiers, alkyl aconitates, were synthesized according to a green process and were characterized by their hydrophilic and lipophilic balance (HLB) and their critical micelle concentration (CMC). These mono-, di and tri-dodecyl aconitates (8%) were effective in stabilizing an oil-in-water emulsion including the natural U. lactuca extract. The viscosities of resulting emulsions helped to form a film on the orange surface. Several in vitro microbiological tests towards Penicillium digitatum showed interesting anti-fungal activities for the new ingredients, as well as for the resulting emulsions. In-vivo tests also confirmed that mono-, di- and tri-docedyl aconitates could contribute to limit the development of P. digitatum on peel surface. Thus, the compositions of two ecofriendly emulsions combining a natural extract and a biobased emulsifier seem adapted to improve oranges preservation.