Aramrueang, N; Asavasanti, S; Khanunthong, A
A great variety of different leafy vegetables comprise one-fifth of the US vegetable market, and account for more than one-third of the fresh produce market. Along with the increase in the production and harvested area, numerous leafy by-products are neglected and underutilized while they have a great potential for producing nutraceuticals, chemicals, energy, and fertilizer. Both leafy primary crops and their by-products share the similarities in characteristics and chemical composition, as the major by-products of leafy vegetables are outer and damaged leaves, core, stalk, and root base. Leafy vegetables and their by-products are a good source of phytochemical compounds, including carbohydrate, protein, dietary fibers, minerals (K, Ca, Mg, P, Fe, Zn, and Mn), vitamins (vitamins A, B complex, and C, and carotenoids), and pigments. Integrated processing technology for extracting organic phytochemicals from leafy by-products for pharmaceutical compounds and food colorants is discussed. Advanced extraction methods have been developed by integrating the new techniques, such as enzyme-assisted extraction, supercritical fluid extraction, pressurized liquid extraction, ultrasound-assisted extraction, microwave-assisted extraction, and pulsed electric field extraction. Anaerobic digestion technology for energy production and nutrient recovery is addressed for sustainable agriculture development. Most leafy by-products showed viable methane potentials and nitrogen fertilizer recovery along with the other minerals.