Citrus Fruits and Their By-Products: Origin, Bioactive Compounds, and Sustainable Valorization Strategies

Citrus fruits are among the most widely cultivated and consumed crops worldwide, exhibiting a complex evolutionary history driven by extensive hybridization and genomic admixture. They are widely appreciated for their sensory quality, rich nutritional composition, and health-promoting benefits, as well as for their significant contribution to the global economy. Considering the growing interest in citrus crops and particularly in citrus by-products as valuable natural resources, as evidenced in the comprehensive literature search, this study provides an overview of recent advances in our understanding of citrus origin, genetic diversity and global production trends. It also examines the phytochemical composition of citrus fruits and by-products and discusses the biological activities associated with these constituents, including antioxidant, antimicrobial and anti-inflammatory effects, as well as their potential health benefits. Additionally, conventional and environmentally friendly strategies for the utilization of citrus residues are presented within a biorefinery framework, with particular emphasis on the recovery and valorization of bioactive compounds. These circular economy approaches highlight the potential use of citrus by-products as valuable raw materials for applications in food, cosmetic and pharmaceutical fields. Overall, this review aims to provide a better understanding of citrus history, composition and potential applications that could support the sustainable and resource-efficient use of citrus substrates in industrial practice for the development of high-value products.