Nanoemulsion-Based Enhancement of the Antifungal Activity of Clove and Ginger Essential Oils Combination against Fungi Causing Papaya Rot.

Recent advances in nanotechnology offer promising solutions for controlling postharvest fungal diseases, a primary cause of economic losses in Carica papaya production. This study assessed the antifungal activity of essential oils (EOs) from Syzygium aromaticum buds (BSA) and Zingiber officinale rhizomes (RZO), alone and in combinations, as well as their nanoemulsion, against Colletotrichum gloeosporioides, Fusarium equiseti, and Lasiodiplodia theobromae, the main pathogens causing papaya rot. EOs were extracted, characterized by GC-MS, and tested individually or in combinations (v/v: 70/30, 50/50, 30/70: BSA/RZO) via the food poisoning method. The optimal combination (70/30: BSA/RZO) showed synergistic effects (FICI: 0.4869-0.8615) and was formulated into a nanoemulsion (NEOco_70/30: BSA/RZO) using low-energy emulsification. The nanoemulsion exhibited a polydispersity index of 0.1330, specific surface area of 2.9 m2/g, mean droplet size of 130 nm, and zeta potential of 34 mV, with excellent physicochemical and rheological stability. EO_BSA was dominated by eugenol (88.08%) and caryophyllene (6.20%), while EO_RZO featured α-zingiberene (22.64%) and geranial (18.76%). NEOco_70/30: BSA/RZO displayed in vitro mycelial inhibition, with MICs of 75 µL/L, 125 µL/L, and 200 µL/L against C. gloeosporioides, F. equiseti, and L. theobromae, respectively. In situ on papaya fruits, it fully prevented necrosis (100% inhibition) at 1250 µL/L in preventive assays and reduced it by 93.24% at 1500 µL/L in curative tests. The combined EO nanoemulsion was more effective than the individual raw EOs and their combinations. These findings underscore the potential of EO nanoemulsions (NEOco_70/30: BSA/RZO) as eco-friendly alternatives to synthetic fungicides for postharvest protection of papaya.