Valorization of Lemon, Apple, and Tangerine Peels and Onion Skins–Artificial Neural Networks Approach

What if your kitchen scraps could become a treasure trove of antioxidants? A new study shows that onion skins and tangerine peels, when zapped with ultrasound, outperform other methods in extracting these health-boosting compounds.

In the quest to turn agricultural waste into valuable ingredients, scientists are testing modern extraction techniques. This study pitted ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE) using water against traditional maceration with natural deep eutectic solvents (NADES). The materials? Apple, lemon, and tangerine peels, plus onion skins—all common by-products that often end up in the trash.

The results were striking. UAE emerged as the champion, especially for onion skins and tangerine peels. Onion skins extracted via UAE delivered the highest total phenolic content (5.735 mg CAE/g) and total flavonoid content (1.973 mg RE/g), along with the strongest antioxidant activity (EC50 = 0.549 mg/mL; IC50 = 0.108 mg/mL). Tangerine peels also shone, with high phenolic content and impressive free radical scavenging power.

To make sense of the data, the team built artificial neural network (ANN) models with high accuracy (r² > 0.96). These models, along with sensitivity and error analyses, highlighted that the extraction method and by-product type are the key drivers of antioxidant yield. Principal component and cluster analyses further revealed that UAE and MAE behave similarly, setting them apart from maceration.

This research underscores the potential of combining UAE with smart modeling to unlock the hidden value in food waste—a win for both science and sustainability.

Key Points

• UAE beats MAE and maceration for antioxidant extraction.
• Onion skins yield highest TPC and TFC via UAE.
• ANN models predict extraction with r² > 0.96.