Metabolomic Profiling, Box–Behnken Design-Based Optimization of Ultrasonic Extraction, and Skin Anti-Aging Potential of the Green Husk of Juglans regia L. as a Sustainable Natural Waste

What if the hairy green husk of a walnut—usually tossed aside as waste—holds the secret to youthful skin? Scientists found 41 phenolic compounds in this discarded peel, and optimized its extraction to boost anti-aging power.

Walnuts are loved for their tasty kernels, but their green husk is often discarded. Now, researchers have shown this humble waste is a treasure trove of bioactive compounds with serious skin anti-aging potential. Using ultrasonic-assisted extraction combined with natural deep eutectic solvents (NADES)—a greener alternative to conventional solvents—they aimed to maximize both phenolic content and elastase inhibition, a key enzyme that breaks down skin elasticity.

To find the sweet spot, the team employed a Box–Behnken Design, testing three variables: NADES/water ratio, temperature, and extraction time. The optimal conditions—99.79% NADES (ethanol), 51.30°C, and 49.58 minutes—achieved a perfect desirability score of 1. This means the extraction was both highly efficient and reproducible.

Metabolomic analysis via LC-qTOF/MS identified 41 phenolic compounds across 27 ontological groups, with 24 of them showing increased semi-quantitative levels under optimized conditions. This diversity and abundance of phenolics likely drive the enhanced elastase inhibition, pointing to the husk's potential as a sustainable ingredient for anti-aging skincare.

By turning agricultural waste into a valuable resource, this study not only offers a green extraction method but also a win-win for both beauty and the environment.

Key Points

• Optimal extraction: 99.79% NADES, 51.30°C, 49.58 min, desirability 1.
• 41 phenolic compounds identified; 24 showed increased levels.
• Waste green husk boosts elastase inhibition for anti-aging.