Natamycin treatment to control postharvest mold development and improve storability of citrus fruits

Green and blue mold caused by Penicillium digitatum and Penicillium italicum, respectively, are the most harmful citrus fruit post-harvest pathogens. In this work, in vivo antifungal effect of Generally Recognised as Safe (GRAS) food additive natamycin pre-treatment was evaluated on artificially inoculated oranges and lemons for the control of green and blue mold during storage. Furthermore, the physico-chemical and other quality properties of the citrus fruits were evaluated after each treatment. Postharvest spray application of natamycin (NT) as low as 4.5 mg/ml on oranges infected by P. italicum significantly reduced the incidence of the disease from 90-100% in the control to 50% after 4 weeks. On infected lemons, the incidence of P. digitatum was significantly reduced by 5 mg/ml NT and resulted in 80% decay after 2 weeks, while control samples were fully spoiled. Various amounts of NT impregnated paper wrappers were tested to determine effectiveness in preserving the quality of the citrus fruits with respect to fruit deterioration. The 5 mg/ml NT impregnated paper wrap gave an improvement with the reduction of 40% of decay after 4 weeks of storage. In general, NT-treated paper wrap application was more effective than spray treatments in controlling both blue and green mold diseases on the surface citrus fruits and extending storage duration up to additional 2-3 weeks. External and internal physico-chemical quality parameters (decay incidence, colour development, loss of firmness, soluble solids and acidity) of fruits were evaluated. NT treatment may offer a combination mean to control postharvest fungal development of fresh citrus fruit.