Flavonoid and main aroma-active compounds identification of Taiwan Citrus depressa Hayata’s peels

Abstract

Citrus peels are a known source of flavonoids and pleasant aroma compounds. Flavonoid compounds in peels of Taiwanese Citrus depressa Hayata (shiikuwasha) were extracted using microwave-assisted extraction (MAE) and ultrasonic-assisted extraction (UAE). Different solvents like distilled water, 50% aqueous ethanol, and methanol were used. The qualitative analysis was carried out by observing UV/Vis and FTIR-ATR spectra, and then quantitatively by High Performance Liquid Chromatography – Diode Array Detector (HPLC-DAD). The composition of volatile aroma components was analyzed using GC-HS-SPME (Gas Chromatography, Head Space Solid Phase Microextraction). UV/Vis analysis showed highest intensity at samples that treated by MAE in 50% aqueous ethanol. HPLC DAD quantitatively confirmed UV results by showing that MAE with ethanol showed higher amounts of quercetin, myricetin, rutin, and kaempferol (670.00, 0.36, 8282.52, 7307.51 µg/g), compared to UAE (336.17, 0.20, 5000.62, 4469.15 µg/g), respectively. FTIR-ATR (Fourier-Transform Infrared Spectroscopy-Attenuated total reflectance) showed typical vibrations at phenolic compounds fingerprint area. Unlike quercetin as flavonoid standard, shiikuwasha peels extract showed peak at polymethoxyflavones (PMF) area (2829 – 2835 cm-1). Fresh and dried unripe peels mostly contained limonene (53.01 – 54.79%), γ-terpinene (27.67 – 29.41%), pinene, myricene and cymene (1.61 – 3.20%) as aroma-active compounds.