Minerals, phenolic compounds, and antioxidant capacity of citrus peel extract by hot water

Some dried citrus peels, more familiar as chenpi in China, have been widely used in traditional Chinese medicines from ancient times. This paper reports the efficiency of infusion cooking on extracting minerals and phenolic compounds (flavanone glycosides [FGs], polymethoxylated flavones [PMFs], and phenolic acids), and also antioxidant activity of hot water extract of citrus peels. Peels of 2 citrus varieties, namely, Satsuma mandarin (C. unshiu Marc.) and Ponkan (C. poonensis Hort. ex Tanaka), which belong to C. reticulata, were selected. As a result, hot water extraction was efficient in extracting phenolic acids and some minerals. As for citrus flavonoids, narirutin, nobiletin, and tangeretin were easier to extract than hesperidin. The result of antioxidant capacity assays indicated that for citrus peels, hot water extract had almost the same capacity as the methanol extract. We suggested that Ponkan was more suitable as the source of chenpi, since its hot water extract had much higher content of phenolic acids, FGs and PMFs, and higher antioxidant capacity than those of Satsuma mandarin. Generally, to raise the extraction temperature or to prolong the time could not yield higher content of phenolic compounds and stronger antioxidant capacity, though the content of minerals increased to some extent. Furthermore, a 2nd-time extraction seemed necessary since considerable minerals and phenolic compounds could be obtained by doing so. Finally, we suggested that 2 times extraction at 100 degrees C for 30 min was proper to extract the minerals and phenolic compounds in chenpi.