Valorization of phenolic compounds from Allium cepa peels: extraction, food and industrial applications, and microencapsulation-a comprehensive review.

Onion is one of the most consumed and produced vegetables globally, recognized for its widespread health benefits and nutraceutical properties attributed to its rich composition of bioactive compounds with diverse biological activities. The postharvest, consumption, and industrial processing of onions generate substantial amounts of by-products, posing significant environmental and socioeconomic challenges. Given that these by-products are also abundant in bioactive compounds, a potential strategy for their valorization and mitigation of their adverse impacts involves extracting these compounds and their application in various sectors, particularly the food industry. This study aims to conduct a comprehensive review of the diverse applications of onion by-product extracts across various fields to understand current trends in the literature and highlight key findings. Furthermore, many bioactive compounds present in onion by-products exhibit limited applicability and low stability under external factors. To address these limitations, microencapsulation emerges as a promising strategy. This work also emphasizes the various microencapsulation techniques applicable to onion by-products, aiming to identify the most effective approaches and optimal conditions. Ultimately, this review seeks to identify existing knowledge gaps and outline future challenges and perspectives related to the valorization of onion by-products, thereby providing insights into strategies that may mitigate their negative impacts.