Effect of Ultrasonic Frequencies on the Aqueous Extraction of Polyphenols, Chlorogenic Acid, and Quercetin from the Whole Fruit of Pitaya (Hylocereus spp.)

The effect of ultrasonic frequencies of 40 kHz/300 W (U-40) and 120 kHz/300 W (U-120) on the aqueous extraction of bioactive compounds from dried whole-fruit powders (DPs) of red-peel/white-flesh (WFP) and red-peel/red-flesh (RFP) pitayas was investigated, and shaking at 120 rpm (S-120) was used for a comparison. The effects of temperature and the solid-to-liquid ratio on the extraction efficiencies of the total phenolic content (TPC) and ferric-reducing antioxidant power (FRAP) of WFP and RFP were evaluated. The impact of extraction time on the aqueous extraction of specific compounds, namely, chlorogenic acid (CGA) and quercetin, from WFP and RFP was assessed with extraction modes of U-40, U-120, and S-120. At 40 °C and a 1/20 (g DP/mL) solid-to-liquid ratio, the use of U-40 achieved higher TPC and FRAP values at 15 min than U-120 and S-120 for WFP. The use of U-40 and U-120 extracted higher amounts of free CGA and free quercetin from WFP and RFP at 15 and 60 min than S-120 but showed different extraction efficiencies for free CGA and free quercetin. This study demonstrates that different ultrasonic frequencies can be applied in the green extraction of target bioactive compounds for use in nutraceutical foods.