Phenolic Components and Health Beneficial Properties of Onions

Onions are a widely cultivated and consumed vegetable, and contain various bioactive components, which possess various health benefits, such as antioxidant, anti-obesity, and anti-diabetic properties. As the major bioactive constituents in onions, it is essential to study phenolic compounds and the heath beneficial properties of onion and its by-products. The bioactivity of phenolic components in onions can be affected by many factors, including the genotype, different growing environments and food processing methods. Currently, most reviews have focused on an investigation of the chemical compounds or bioactivity of raw onions, but there is a paucity of studies concerning whether pre-harvest (i.e., genotype and growing environment) and post-harvest (i.e., storage) factors can impact its phenolic compounds. This review provides knowledge and guidance to agricultural production on producing high-quality onions and to the food industry on developing functional foods to reduce some chronic diseases such as diabetes. It also promotes research interest in studying bioactive compounds in fruits and vegetables considering different pre-harvest and post-harvest conditions.