Apple Pomace as a Source of Valuable Phenolics: From Drying Kinetics to Optimization of Ultrasound-Assisted Extraction Using Conventional and Alternative Solvents

Did you know that nearly a third of every apple ends up as waste? But this pomace is a goldmine of health-boosting compounds, and scientists just found a greener way to unlock them.

When apples are crushed for juice or cider, up to 30% of the fruit becomes pomace—seeds, skin, and pulp. This byproduct is packed with fiber, vitamins, and polyphenols, but it's often discarded. Now, researchers are turning this waste into a treasure trove of bioactive compounds.

The study compared two drying methods—hot-air convection and infrared—to see how they affect polyphenol preservation. Both methods changed color and antioxidant content, with higher temperatures showing a surprising benefit: they partially inactivated browning enzymes, preserving more of the good stuff. Infrared drying came out ahead, using less energy and time.

For extraction, the team tested ultrasound-assisted extraction with various solvents. A natural deep eutectic solvent made from choline chloride and glycerol (1:1) outperformed conventional solvents, pulling out more phenolics with high antioxidant activity. Optimization of this process yielded an extract rich in flavan-3-ols like catechin and epigallocatechin, plus chlorogenic acid.

This work shows that apple pomace is not just waste—it's a valuable source of health-promoting compounds, and polyol-based NaDES offer a sustainable, efficient way to recover them.

Key Points

• Apple pomace is 25–30% of fresh fruit mass, rich in polyphenols.
• Infrared drying beats hot-air in speed and energy use.
• Choline chloride-glycerol NaDES optimally extracts phenolics.