Evaluation of the Phenolic Content, Antioxidant and Antimicrobial Activities of Oil and Non-Oil Extracts of Citrus sinensis (L.) Osbeck Seeds

The seeds of Citrus sinensis (L.) Osbeck (sweet orange) are waste products usually discarded. They may however contain phytochemicals that have potent bioactivities. In this study, the phenolic content, and antioxidant and antimicrobial activities of oil and non-oil (solid) extracts of C. sinensis seeds were evaluated using standard protocols. The seed oil contained significantly (P>0.05) higher contents of total phenol and total flavonoid when compared to the solid extract. However, the non-oil extract contained significantly (P<0.05) higher tannin contents than the seed oil. Ferric reducing antioxidant potential was not significantly different between both extracts. The antimicrobial activities of both extracts revealed that the seed oil possesses better antibacterial activities compared to the non-oil extract. The antifungal test revealed that the seed oil significantly inhibited the growth of Candida albicans (20 mm zone of inhibition at a concentration of 200 μg/mL), however, it did not inhibit the growth of Aspergillus niger and Penicillum sp. The minimum inhibitory concentration values against the bacterial and fungal strains were similar for both extracts in the range of 50∼100 μg/mL. Minimum bactericidal concentration and minimum fungicidal concentration values ranged from 100∼200 μg/mL for both extracts. The results in this study indicate that C. sinensis seed oil and non-oil extracts possess antioxidant, and antibacterial and antifungal properties that may be differentially exploited in the development of antimicrobial agents.