Onion peel waste (OPW), a major by-product of the agri-food industry, represents an underutilized biomass rich in valuable polysaccharides such as pectin. Addressing the need for sustainable valorization strategies, this study explores the transformation of OPW into pectin-derived compounds (PDCs) through a continuous subcritical water (SubW) extraction process conducted without chemical additives. The method leverages rapid hydrolysis at 200 °C with a residence time of approximately 5 s, markedly outperforming conventional batch (150 min at 125 °C) and semicontinuous systems in terms of efficiency and selectivity. The severity factor was applied to compare different reactor configurations, demonstrating the enhanced performance of the continuous process. This system maintained PDC yields of up to 30 %, preserved polymer integrity, and yielded compounds with significantly higher molecular weight (108 kDa vs. 78 kDa in batch). Furthermore, it reduced the formation of degradation products such as formic acid and furfural, resulting in a purer extract and facilitating downstream purification. These findings underscore the importance of precise control over extraction time to enable higher processing temperatures without compromising product quality. Overall, continuous SubW extraction emerges as a scalable, energy-efficient, and environmentally friendly approach for producing high-purity PDCs with potential applications in the food, pharmaceutical, and cosmetic industries. This work contributes to the advancement of the circular bioeconomy by promoting the upcycling of agricultural residues into high-value bioproducts.

中文翻译：

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通过连续纯水萃取将洋葱废料升级回收为果胶衍生化合物

洋葱皮废料 （OPW） 是农业食品工业的主要副产品，是一种未充分利用的生物质，富含果胶等有价值的多糖。为了满足对可持续增值策略的需求，本研究探讨了通过无化学添加剂的连续亚临界水 （SubW） 提取过程将 OPW 转化为果胶衍生化合物 （PDC）。该方法利用 200 °C 的快速水解，停留时间约为 5 s，在效率和选择性方面明显优于传统间歇系统（125 °C 下 150 分钟）和半连续系统。应用严重性因子来比较不同的反应器配置，证明连续工艺的性能得到增强。该系统将 PDC 产量维持在高达 30% 的水平上，保持了聚合物的完整性，并产生了分子量显著提高的化合物（批量 108 kDa 对 78 kDa）。此外，它还减少了甲酸和糠醛等降解产物的形成，从而获得更纯净的提取物并促进下游纯化。这些发现强调了精确控制提取时间的重要性，以便在不影响产品质量的情况下实现更高的加工温度。总体而言，连续 SubW 萃取是一种可扩展、节能且环保的方法，可用于生产高纯度 PDC，在食品、制药和化妆品行业具有潜在应用。这项工作通过促进农业废弃物升级再造为高价值生物产品，为推进循环生物经济做出了贡献。