Comparison of Lipid Peroxyl Radical Scavenging Activity and Total Phenolic Content of Four Selected Citrus Species Leaves Extract

In this study, water and 80% methanol extracts of Citrus aurantifolia, C. hystrix, C. maxima, and Citrofortunellamicrocarpa leaves were prepared. The lipid peroxyl radical scavenging activity of the extracts was determined by β-carotene bleaching method, whilst their total phenolic content was assessed by Folin-Ciocalteu method. An interesting pattern was observed where the scavenging activity and total phenolic content of Citrus water extracts are higher than that of the respective methanolic extracts. Scavenging activity in water extract of C. maxima leaves is the highest (81±1.6%), followed by Citrofortunellamicrocarpa (79.7±2.3%). These activities are not significantly different from the positive control—butylated hydroxytoluene (BHT) (82.91±0.9%)—indicating strong antioxidant activity of both Citrus extracts. The highest total phenolic contents showed by water extract of Citrofortunellamicrocarpa leaves (585.7 ± 5.8 mg GAE/100 g of fresh weight citrus leaves), whereas total phenolic contents of other water and methanol extracts are below 400 mg GAE/100 g of fresh weight citrus leaves. Importantly, the scavenging activity in both water and methanol extracts are positively correlated with the phenolic content. However, the correlation of scavenging activity with phenolic content is stronger in the 80% methanol extracts (r= 0.605) than in the water extracts (r=0.46). In conclusion, among all the citrus extracts, Citrofortunellamicrocarpa water extract exhibited higher total phenolic content and lipid peroxyl radical activity. Correlation analysis infers that the free radical activity is not only contributed by phenolic content of the water extract.