Study on antimicrobial and antioxidant capacity of extracts from citrus peels and seeds

Abstract

The antimicrobial and antioxidant of ethanol solvent extracts from three varieties of citrus fruit peels and seeds were tested under different methods and determined its properties to serves as an good natural sources of bioactive compounds. Peels and seeds extracts of Vinh orange (Citrus sinensis Osbeck), Thanh Tra pomelo (Citrus grandis Osbeck) and Dao lime (Citrus hybrid – Citrus spp.) were tested antimicrobial activities of four bacteria strains and two fungal strains by diffusion method and dilution method. The result of the test on four bacterial strains, include Staphylococcus aureus, Bacillus cereus, Salmonella typhi and Pseudomonas aeruginosa, showed great inhibition ability by the citrus extracts. Pomelo seed and peel extracts had strongest inhibition against B.cereus and S.typhi compared to other extractions (14.08±1.01mm, 12.50±0.50mm and 14.42±0.63mm, 14.40±0.53mm), and they also had quite low minimum inhibitory concentration (MIC) against B.cereus and S.typhi at concentration about 80mg/ml. Moreover, lime seed and peel got strongest inhibition against S.aureus with 16.17±0.76mm and 15.42±0.52mm, following by lowest MIC at concentration of 20mg/ml. Unfortunately, the gram-negative P.aeruginosa as well as two fungi could not been inhibited in this study due to its structure and the citrus extracts components. The antioxidant activities of these citrus extractions were determined by Ferric Thyocyanate (FTC) assay. The antioxidant in contrast with antibacterial provided that orange peels and lime peels had the lowest AA50 (84.60 and 84.08mg/ml respectively) as well as highest antioxidant capacities. Pomelo peels were highest AA50 (108.86mg/ml). It was the same with citrus seed (orange seed were 93.68mg/ml, then lemon seed 94.45mg/ml and pomelo seed 105.16mg/ml). In general, almost all the peels extracted had the inhibitory capacity against the oxidation of linoleic acid higher than those seeds. According to the results, extraction of peels and seeds (without oil) of different Citrus varieties may have different antimicrobial and antioxidant activities. Key words: citrus peels extracts, citrus seeds extracts, antimicrobial activities, antioxidant activities, ethanol solvent extracts.