Carboxymethyl cellulose/Tween 80/Litsea cubeba essential oil nanoemulsion inhibits the growth of Penicillium digitatum and extends the shelf-life of ‘Shatangju’ mandarin

Penicillium digitatum (P. digitatum) is the primary pathogenic fungus responsible for postharvest citrus green mold, leading to a deterioration in fruit quality and significant economic losses. Litsea cubeba essential oil (LCEO) has gained widespread attention as a natural antifungal substance due to its high safety profile, non-resistance traits, and broad-spectrum antifungal activity. In this study, we prepared Litsea cubeba essential oil nanoemulsion (LCEO-NE) using Tween 80 and carboxymethyl cellulose (CMC) as emulsifiers through ultrasonic emulsification. The investigation delved into their stability, rheology, inhibitory activity against P. digitatum, and efficacy in preserving ‘Shatangju’ mandarin during storage. The results showed that the droplet size, polydispersity index, and zeta potential were 18.69 nm, 0.116, and −29.72 mV, respectively. LCEO-NE added with CMC and Tween 80 synergistically (LCEO-NE-CMC) have exhibited higher pH stability, ionic strength stability, thermal stability, storage stability, and centrifugal stability compared to LCEO-NE with Tween 80. In vitro fungistatic tests revealed that the minimum inhibitory concentration (MIC) and minimum fungicidal concentration (MFC) of LCEO-NE-CMC against P. digitatum were 1 μL mL−1 and 2 μL mL−1, respectively. LCEO-NE-CMC effectively inhibited mycelium growth, spore germination, and elongation of germ tubes. Scanning electron microscopy results demonstrated that LCEO-NE-CMC caused wrinkling and twisting of P. digitatum mycelium. Transmission electron microscopy results further revealed severe damage to the cell membrane, cytoplasm, and organelles, hindering mycelial growth. Furthermore, LCEO-NE-CMC treatment of ‘Shatangju’ mandarin significantly reduced weight loss and decay rate and delayed the decline in hardness and total soluble solids. In summary, LCEO-NE-CMC has been validated as a potent antifungal agent capable of extending the shelf life of ‘Shatangju’ mandarin.