Extraction of nobiletin from Citrus Unshiu peels by supercritical fluid and its CRE-mediated transcriptional activity

BackgroundPolymethoxyflavone (PMF) is one of bioactive compounds in Citrus Unshiu and included mainly in the peels rather than the fruits, seeds and leaves.Hypothesis/PurposeSupercritical CO2 extraction is one candidate for selective extraction of polymethoxyflavone and in this study, supercritical CO2 extraction with/without ethanol entrainer from Citrus Unshiu peels was examined at a temperature of 333 K and a pressure of 30 MPa.MethodsCRE (cyclic AMP response element)-mediated transcriptional assay was examined by using the extracts from supercritical fluid extraction.ResultsThe results showed that extracts including nobiletin increased with increasing ethanol concentration in supercritical CO2 and the elapsed extraction time. Extracts at ethanol concentration of 5 mol% showed high CRE-mediated transcription activity. This can be caused by activity of the extract including nobiletin in addition to the other methoxylated flavonoid species such as tangeretin. Extracts at ethanol concentration of 50% showed the highest CRE-mediated transcription activity, which can be attributed to flavonoid glycoside such as hesperidin. From our investigations, flavonoid glycoside can be one of promoters of CRE-mediated transcription activity.

CRE (Cyclic AMP response element) dependent transcription-stimulating activity (pCRE/pRG-TK activity) of extracts from supercritical CO2 with/without ethanol. Ethanol concentration of 0 mol%, 5 mol%, 10 mol%, 20 mol% and 50 mol% show bars from left hand side to right hand side, respectively. Nobiletin in all standard and extracts was controlled at 1 µM.90