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In the cultivation of Citrus fruit, pruning in late winter after harvest is important to obtain excellent flower buds in the next spring and a rich harvest of superior fruit in the following winter; a large number of pruned leaves are usually discarded. The purpose of this study was to determine the utility value of pruned leaves of Citrus unshiu. A methanol extract of pruned C. unshiu leaves showed a porcine pancreatic lipase inhibitory activity. Fractionation of C. unshiu leaf extract (CUL-ext) followed by bibliographic and chromatographic analyses revealed that a part of the pancreatic lipase inhibitory activity of CUL-ext was attributable to nobiletin (1), rutin (2), and hesperidin (3). Thus, pruned C. unshiu leaves may be a reasonable natural resource for the preparation of ingredients with lipase inhibitory activity.

In our research program for discovering novel skin-whitening materials, screening of extracts from flowers of some Prunus species was performed using an anti-tyrosinase assay. Among the tested plants, the flowers of P. persica showed the most potent inhibitory activity. In addition, P. persica also showed suppression of melanogenesis in B16 rat melanoma cells. The active principles of tyrosinase inhibition and suppression of melanogenesis were revealed to be an afzelin (3- O-α-L-rhamnosylkaempferol) and a flavanone, naringenin. The mechanism of the anti-melanogenesis effect of these two compounds was disclosed, for the first time, as the suppression of the expression of tyrosinase protein, which was controlled by the inhibition of phosphorylation of p38 MAPK. These findings show that these compounds could be candidates for the novel molecular target for a skin-whitening agent.