STRATEGIES FOR CONTROLLING PENICILLIUM DIGITATUM IN ORANGES USING ACTIVE BIOPOLYMERIC COATING

Penicillium digitatum is responsible for green mold in citrus, leading to substantial postharvest losses. The development of active coatings represents a promising approach to mitigating fruit deterioration and extending shelf life. This study developed several formulations based on sodium alginate (SA) and carboxymethylcellulose (CMC), incorporating the biosurfactant monorhamnolipid (mono-RML) at concentrations determined by the minimum inhibitory concentration (MIC) against P. digitatum. Solutions containing SA (1.0% w/w), CMC (0.5% w/w), and glycerol (20% mglycerol/mpolymers) were prepared, with mono-RML added at three concentrations: 1× MIC (775 mg/L), 3× MIC (2325 mg/L), and 6× MIC (4650 mg/L). Each formulation (500 µL) was spread on sterile potato dextrose agar (PDA) plates. A sterile paper disk was placed at the center of each plate and inoculated with 10 µL of P. digitatum suspension (10⁵ CFU/mL). Colony diameter was measured after eight days of incubation at 25 °C in BOD. Antifungal activity was assessed using the mycelial growth inhibition assay (MGI%). Additional tests were conducted on ‘Pêra’ oranges to evaluate the effectiveness of the active coating in controlling postharvest fungal lesions. The treatments included: (i) oranges coated with the active polymeric solution (SA/CMC/mono-RML 6× MIC), (ii) application of a commercial fungicide (Graduate A+), and (iii) an uncoated control. Artificial lesions with approximately 6 mm in diameter were produced on the fruit epidermis using a scalpel. Treatments were applied, and after drying, 10 µL of P. digitatum spore suspension (10⁶ CFU/mL) was inoculated onto the lesions. Fruits were stored at 25 ± 1 °C and 80–95% relative humidity for seven days. The SA/CMC polymeric solution without mono-RML showed no inhibition in vitro. In contrast, coatings containing 1× MIC, 3× MIC, and 6× MIC reduced P. digitatum mycelial growth by 44.95%, 56.69%, and 67.07%, respectively, with statistically significant differences among treatments. The formulation with the highest MGI (6× MIC, 4650 mg/L) was selected for application to oranges. After seven days of storage, uncoated fruits exhibited disease symptoms in 100% of samples, while fruits treated with the active coating (6× MIC) or synthetic fungicide showed only 11% of infection. These findings indicate that the bioactive coating is highly effective in protecting wounded fruits, likely by forming a protective barrier at injury sites where the risk of postharvest infection is greatest.