Ursolic acid nanoemulsion system for inhibition of goji berry black mold caused by Alternaria alternata.

Ursolic acid (UA) possesses antifungal activity against A. alternata, however, its poor solubility poses a challenge for practical application. We prepared UA nanoemulsions consisting of ethyl oleate, Cremophor EL, and Transcutol HP. The particle size of the UA nanoemulsions ranged from 20.53 to 27.88 nm. Electron microscopy revealed a nearly spherical structure. Fourier-transform infrared analysis proved that UA was successfully encapsulated, and the encapsulation efficiency ranged from 82 to 84%. UA nanoemulsions showed stable characteristics for 15 days of storage. The minimum inhibitory concentration of UA nanoemulsions against A. alternata was 0.8 mg/mL. UA nanoemulsions suppressed hyphal growth, reduced the spore yield and germination rate, and shortened the length of germ tubes in A. alternata. In vivo experiments confirmed that UA nanoemulsions could inhibit the goji berries and apple fruits infected by A. alternata. Collectively, these results demonstrate that UA nanoemulsion shows strong antifungal potential for postharvest rot control.