Antimicrobial and antioxidant activities of different extracts of the peel of kumquat (Citrus japonica Thunb)

Abstract

The objective of this work was to study the bioactive properties of kumquat fruit (Citrus japonica thumb)peel. The mineral composition (ICP-MS), phenolic and flavonoid contents (HPLC), volatiles (GC–MS), antioxidant activity (DPPH) and antimicrobial activity of kumquat peel were determined. Kumquat peel was found to be a good supplement of K, Mg, Ca and Na. The major phenolic acids found were p-hydroxybenzoic acid that followed by vanillic, protocatechuic, chlorogenic and sinapic acids, respectively. The extract contained also apigenin 7-glucosideflavonoid. The volatiles oil analysis showed that kumquat peel essential oil was rich in monoterpenoid limonene (96.33%). The oil was also composed of considerable amount of d-germacrene, α-myrecene, and α-pinene and minor amount of bicyclogermacrene and sabinene. The highest antioxidant activity was obtained using 70% ethanol extract (55.47%), while the least one was observed with n-hexane (27.05%). The antioxidant activity of kumquat extract increased from (21.31%) when the extract concentration was (63 µg/100 µl) to (64.98%) with concentration of (1000 µg/100 µl). Regarding the antimicrobial activity, the highest zone of inhibition (16.58 mm) was recorded with 70% ethanol extract, while the least zone of inhibition (8.98 mm) was found with acetone extract. Staphylococcus aureus was the most sensitive organism with the highest zone of inhibition (16.70 mm) and Escherichia coli was the most resistant organism with the least zone of inhibition (11.30 mm). The present study reviewed antioxidant and antimicrobial activity of different extracts of kumquat peel and concluded that kumquat peel might be used as a natural bioactive source, mainly in the food and pharmaceutical industries.