Phytochemical Analysis and Antifungal Activities of Citrus limon and C. sinensis Peel Extracts

Fusarium dry rot (Fusarium solani) and Pythium aqueous rot (Pythium ultimum) are important post-harvest diseases responsible annually for regrettable qualitative and quantitative losses during potato (Solanum tuberosum L.) storage. Processing waste of citrus fruits is considered an eco-friendly and bio-safe alternative to traditional agrochemicals due to their excellent repository of bioactive compounds. The present study assessed chemical composition, antifungal activities, antioxidant assays and total phenolic and flavonoid contents of essential oils and aqueous extracts from peels of Citrus limon and C. sinensis. The aqueous extracts were obtained by maceration, and phytochemical screening was performed by HPLC. The essential oils were extracted by hydro-distillation using the Clevenger apparatus and analyzed by Gas Chromatography–Mass Spectrometry. The total polyphenol and flavonoid contents and antioxidant potential of both citrus peel extracts were investigated spectrophotometrically. The antifungal activities performed by poisoned food technique and disk diffusion method against F. solani and P. ultimum. The results revealed that C. limon peel extracts exhibited higher polyphenol and flavonoids contents compared to C. sinensis. The antioxidant activities of C. limon peels (82.91%) generated a highest activity than C. sinensis (73.51%). The phytochemical analysis of the aqueous extracts indicated the presence of significant concentrations of major phenolic acids (quinic, protocacchuic, caffeic, coumaric and frulic acid). Rutin, kampherol and quercetin considered as major flavonoids. Furthermore, phytochemical profile analysis of essential oil indicated that the major phytochemicals are α-limonene, β-pinene, ɣ-terpinene, β-linalool and α-citral. The peel extracts inhibited mycelia growth of F. solani and P. ultimum. Both post-harvest pathogens were classified as very sensitive to orange and lemon oils. The present study indicates that citrus peels are rich in numerous phytochemicals and bioactive components. In addition, they exhibited a promising potential on inhibiting growth of these pathogenic fungi. Therefore, bioactive compounds of citrus peels with significant antifungal activities have a promising future in Fusarium dry rot and Pythium aqueous rot management to substitute the agrochemicals.