Comparative Analysis of Chemical Compositions and Biological Activities of Kumquat Leaf Oils From Southern Thailand

The essential oil from fresh and dry kumquat leaves (Citrus japonica Thunb.) was extracted and its biological activities were evaluated. The results found that the kumquat leaf oils exhibited the antioxidant activity with dried leaf oil posing higher potency (IC₅₀ = 54.2±3.3 mg mL^-1) than fresh leaf oil (IC₅₀ = 60±0.73 mg mL^-1). Moreover, the kumquat leaf oils showed inhibitory effects against Bacillus subtilis, and Staphylococcus aureus but not against Escherichia coli. Greater potency was observed for the dried leaf oil (MIC and MBC values were 3.9 and 3.9 mg mL^-1, respectively, against B. subtilis, and 7.8 and 7.8 mg mL^-1, respectively, against S. aureus). The kumquat leaf oils could inhibit MCF7 and NCI-H187 cell proliferation. More than 90% of NCI-H187 cells were eliminated at concentrations of 0.976 mg mL^-1 and 1.95 mg mL^-1 for fresh and dried leaf oils, respectively. In the case of MCF7 cells, over 90% of cells were obliterated after incubation with the kumquat leaf oil at a concentration of 7.81 mg mL^-1. However, their anticancer properties were not significantly different (P>0.05) when IC₅₀ values were observed. Thus, the results indicate that kumquat leaf oil possesses remarkable biological activities, highlighting its potential for further in-depth research and development into health-promoting therapeutic agents or products.