Ultrasound‐assisted extraction of phenolic compounds from walnut (<scp><i>Juglans regia</i></scp> L.) shell waste using choline chloride‐based natural deep eutectic solvents (<scp>NADES</scp>): an <scp><i>in vitro</i></scp> bioaccessibility study
Aysenur Erdem, Melek Keskin, Ertürk Bekar, Senem Kamiloğlu
Abstract
BACKGROUND: Walnut shells, which are discarded as waste at both household and industrial levels, are good sources of phenolic compounds. The aim of this study was to apply an ultrasound-assisted extraction method using ten different choline chloride (ChCl)-based natural deep eutectic solvents (NADES) to recover phenolic compounds from walnut shell waste (WSW) and to evaluate the in vitro bioaccessibility of the resulting green extracts. The phenolic compounds were identified and quantified using ultra-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry. RESULTS: The results revealed that quercitrin and taxifolin were the predominant flavonoids in WSW, while ellagic acid was the dominant phenolic acid. Bioaccessible total phenolic content (TPC), total antioxidant capacity (TAC), flavonoids and phenolic acids and aldehydes were higher in most NADES extracts compared to the ethanolic extract. The extracts prepared with ChCl:lactic acid exhibited the highest bioaccessibility for TPC (79%), TAC (72%) and flavonoids (81%), while ChCl:glycerol had the highest levels of bioaccessible phenolic acids and aldehydes (99%). CONCLUSION: This study emphasized the effectiveness of treating WSW with NADES combined with ultrasonication to improve the recovery and bioaccessibility of phenolic compounds. © 2025 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.