Unlocking Value from Waste: a Comparative Study of Orange Peel Extraction Methods Using Choline Chloride-Based Natural Deep Eutectic Solvents

Orange peels are waste no more—scientists are turning them into treasure with cutting-edge green solvents that could keep Vitamin C stable and skin-ready.

Imagine the humble orange peel, discarded by the millions of tons each year. Now, picture it as a goldmine of bioactive compounds, waiting to be unlocked. This study dives into that potential, using Natural Deep Eutectic Solvents (NADES)—eco-friendly liquids made from natural ingredients—to extract and protect ascorbic acid, better known as Vitamin C.

The researchers tested various NADES, measuring their antioxidant power with three different assays: TEAC, DPPH, and ORAC. They simulated Vitamin C solubility using COSMO-Therm software and tracked its degradation over 30 days at two temperatures using HPLC. To see if the vitamin could penetrate biological barriers, they employed the PAMPA method for both skin and gastrointestinal membranes.

Results showed that NADES based on organic acids were more polar than those from sugars or polyalcohols. Interestingly, lower pH increased Vitamin C degradation, but the half-life was longer at 4°C, with choline chloride:xylose emerging as the best stabilizer. Some NADES, like betaine:malic acid, actually performed worse than the control.

The PAMPA study revealed that lactic acid:glucose gave the highest permeability for both gastrointestinal (Log Pe: -4.99) and skin (Log Pe: -4.78), while malic acid:glucose had the lowest (-6.9). This suggests that certain NADES can shield Vitamin C from oxidative harm—a promise that might extend to other bioactive compounds in natural extracts.

Key Points

• Organic acid NADES are more polar than sugar-based ones.
• Choline chloride:xylose best stabilizes Vitamin C at 4°C.
• Lactic acid:glucose shows highest permeability for GI and skin.