Valorization of Taiwan's Hayata peels as a source of nobiletin and tangeretin using simple ultrasonic-assisted extraction.

As the highest yield crop worldwide, citrus peels that possess bioactive compounds were discarded as a futile by-product. Ultrasonication with environmentally friendly solvent (50% ethanol and ddHO) were used in the present study to extract flavonoids from Hayata peels with extraction period and fruit maturity as other variables. DPPH scavenging activity was investigated. Qualitative flavonoid content analysis was done by UV/Vis and FTIR-ATR spectra. Quantification of flavonoid using LC-MS/MS found that solvent type, fruit maturity, and ultrasonication period significantly affect the extracted flavonoid yield (p < 0.05). Extraction using 50% ethanol showed a higher yield than ddHO. Flavonoid content was also higher in unripe than ripe samples. Nobiletin, tangeretin, and rutin were dominant among the identified compounds in all sample treatments. Flavonoid content in Hayata extract was found to negatively correlate to DPPH scavenging activity, which needs further research to identify other bioactivities of these flavonoids.