Citrus by-products valorization using deep eutectic solvents – A review

Orange processing generates 1.3 billion tons of by-products yearly, destined for animal feed or improperly discarded, causing adverse environmental impacts, such as soil contamination, water pollution, and disease transmission, and wasting a large amount of material that could still have a high added value. By-products can be of animal and vegetable origin. The primary by-products generated include peels, pomace, and seeds, recognized for their richness in high-value compounds such as essential oils, carotenoids, phenolic compounds, and vitamins (C and E). These compounds have diverse applications in the food industry, such as dietary fibres, encapsulating agents, and food additives, and their antioxidant, anti-inflammatory, antimicrobial, and anticancer properties. Several conventional extraction methods are used to obtain these valuable compounds. However, these methods have disadvantages, such as longer process time, greater energy consumption, and large amounts of toxic solvents. Recently, deep eutectic solvents have been studied to achieve a green and sustainable extraction process. Deep eutectic solvents are formed by the addition of two or more elements substances capable of donating and receiving hydrogen bonds, forming a eutectic mixture with a lower melting point than its constituents and consequently with improved characteristics for extracting bioactive compounds. Therefore, this article explores the potential of deep eutectic solvents in extracting bioactive compounds from orange by-products, presenting their advantages and main physicochemical properties as a possible alternative to conventional extraction methods.