Lignins are phenolic polymers endowed with potent antioxidant properties that are finding increasing applications in a variety of fields. Consequently, there is a growing need for easily available and sustainable sources, as well as for green extraction methodologies of these compounds. Herein, a ball milling/deep eutectic solvent (DES)-based treatment is reported as an efficient strategy for the recovery of antioxidant lignins from the shells of edible nuts, namely chestnuts, hazelnuts, peanuts, pecan nuts, and pistachios. In particular, preliminarily ball-milled shells were treated with 1:2 mol/mol choline chloride:lactic acid at 120 °C for 24 h, and the extracted material was recovered in 19–27% w/w yields after precipitation by the addition of 0.01 M HCl. Extensive spectroscopic and chromatographic analysis allowed for confirmation that the main phenolic constituents present in the shell extracts were lignins, accompanied by small amounts (0.9% w/w) of ellagic acid, in the case of chestnut shells. The recovered samples exhibited very promising antioxidant properties, particularly in the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay (EC₅₀ values ranging from 0.03 to 0.19 mg/mL). These results open new perspectives for the valorization of nut shells as green sources of lignins for applications as antioxidants, e.g., in the biomedical, food, and/or cosmetic sector.

中文翻译：

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通过基于绿色球磨/深共晶溶剂 (DES) 的协议从食用坚果壳中回收具有强抗氧化特性的木质素

木质素是一种酚类聚合物，具有强大的抗氧化特性，在各个领域的应用越来越广泛。因此，越来越需要容易获得和可持续的来源，以及这些化合物的绿色提取方法。在此，基于球磨/深共熔溶剂 (DES) 的处理被报道为从可食用坚果壳（即栗子、榛子、花生、山核桃和开心果）中回收抗氧化木质素的有效策略。特别是，初步球磨的贝壳用 1:2 mol/mol 氯化胆碱：乳酸在 120 °C 下处理 24 小时，提取物回收率为 19-27% w / w通过添加 0.01 M HCl 沉淀后的产率。广泛的光谱和色谱分析证实，在栗壳的情况下，壳提取物中存在的主要酚类成分是木质素，并伴有少量 (0.9% w / w ) 的鞣花酸。回收的样品表现出非常有希望的抗氧化特性，特别是在 2,2-二苯基-1-苦基肼 (DPPH) 测定中（EC ₅₀值范围为 0.03 至 0.19 mg/mL）。这些结果为坚果壳作为木质素绿色来源的价值提供了新的视角，可用作抗氧化剂，例如在生物医学、食品和/或化妆品领域。