Chin Xuan TanSeok Shin TanHui Ling TanSeok Tyug Tan2025-09-242025-09-2420259783031773983978303177399010.1007/978-3-031-77399-0_3https://dspace-cris.utar.edu.my/handle/123456789/11355Bioactive phytochemicals derived from agro-industrial residues, mainly vegetable and fruit waste, are increasingly popular in the food industry. Onions (Allium cepa L.) are the most commonly consumed crops worldwide. The increased market for processed onions has resulted in a significant accumulation of waste. This chapter provides an overview of the bioactive compounds and proximate and mineral composition of onion by-products. The application of onion by-products is also compiled and discussed. © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2025, corrected publication 2025.enBioactive compoundBy-productFlavonoidOnionSulfurBreweriesDairiesFood industryFruitsVegetablesAgro-industrial residueAllium cepaBioactive compoundsBioactivesFood industriesOnion by-productsPhytochemicalVegetables and fruitsCropsbook-chapter