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

What if the key to unlocking the healthiest compounds in dragon fruit isn't just the fruit itself, but the sound waves you use to shake it? A new study shows that choosing the right ultrasonic frequency can make all the difference.

Dragon fruit, or pitaya, is more than just a pretty face. Its flesh and peel hide a treasure trove of polyphenols, including chlorogenic acid and quercetin, compounds celebrated for their antioxidant power. But how do we get these goodies out efficiently and sustainably? The answer, it turns out, lies in sound.

In a recent study, researchers compared two ultrasonic frequencies—40 kHz and 120 kHz, both at 300 W—against simple shaking at 120 rpm. Using dried whole-fruit powders from red-peel/white-flesh (WFP) and red-peel/red-flesh (RFP) varieties, they extracted bioactive compounds in water, a green and eco-friendly solvent.

At a mild 40°C and a 1:20 solid-to-liquid ratio, the lower frequency (40 kHz) was the star for total phenolic content and antioxidant capacity, achieving higher values in just 15 minutes than its higher-frequency or shaking counterparts, at least for the white-flesh type. Both ultrasonic methods outperformed shaking in pulling out free chlorogenic acid and quercetin from both varieties, though their efficiency varied depending on the target compound.

This work highlights that ultrasonic frequency is not a one-size-fits-all tool. By tuning the sound, we can tailor the extraction of specific bioactives for nutraceutical foods, making the process both greener and smarter.

Key Points

• 40 kHz beats 120 kHz for total phenolics in white-flesh pitaya.
• Ultrasound outshines shaking for extracting free chlorogenic acid and quercetin.
• Green water extraction tuned by frequency for nutraceuticals.