Ultrasound-assisted sustainable extraction of bioactive phytochemicals in shallot (Allium ascalonicum L.) peel: A DoE and metabolomics combined approach

Fruits and vegetables, essential components of human nutrition, undergo considerable losses and waste during processing. Recognizing this issue, this study delves into the potential use of shallot (Allium ascalonicum L.) peels, typically discarded by-products, using ultrasound-assisted extraction (UAE), a green and effective method. Employing the Design of Experiments (DoE) methodology, the study optimized extraction parameters, obtaining an extraction time of 10 min, an amplitude of 47%, and a solid-to-liquid ratio of 1:10. The results revealed a broad diversity of potentially bioactive compounds, including flavonoids (isorhamnetin, delphinidin), phenolic acids (sinapoyltyramine), stilbenes (piceatannol 3-O-glucoside), terpenoids (gibberellin), and sulphur compounds (3-ethylthiophene). Notably, the extract exhibited strong antioxidant activity. Additionally, the study investigated the ability of shallot peel extracts to inhibit key enzymes - alphaglucosidase (Glu), acetylcholinesterase (AChE), and tyrosinase (Tyr) - relevant in carbohydrate metabolism, memory, and skin pigmentation. While demonstrating significant Glu inhibition, no notable AChE or Tyr inhibition was observed. Correlation analysis highlighted the involvement of flavonoids and terpenoids in the bioactivities observed. This research underscores the potential of shallot by-products as a source of valuable compounds with applications in the food and pharmaceutical industries. Further exploration is encouraged to unveil specific bioactive compounds responsible for the antioxidant potential and to harness the full potential of shallot by-products in promoting health and sustainability.