Agriculture waste valorisation as a source of antioxidant phenolic compounds within a circular and sustainable bioeconomy

Planet globalization, population growth and its consequent need to produce large amounts of food, or individual economic benefits and the prioritization of this over environment health, are factors that that have contributed to the development, in some cases, of a linear-producing modern agricultural system. In contrast to traditional and local agriculture, which was based on circular sustainability models, modern agriculture currently produces tons of waste that is accumulated in landfill, creating controversial consequences, instead of being reintroduced into the production chain with a novel purpose. However, these residues from agriculture are rich in bioactive compounds, including phenolic compounds, secondary metabolites that are found naturally in plants, which show antioxidant, anti-inflammatory, cardioprotective and anticancer capacities, among others. Although there are several suitable extractive techniques for isolating these beneficial compounds from agricultural by-products, their industrial application remains without real application value at the industrial scale. The recovery of functional phenolic compounds can be achieved, obtaining products that can be reinserted into the economy as a new raw material. The re-utilization of these compounds not only represents numerous potential applications, such as food and feed additives, functional foods, nutraceuticals, cosmeceuticals, and so forth, but also represents a favourable measure for the environment, and results in the formation of value-added products. This review summarizes all of the aspects that lead to phenolic compound recovery from agricultural wastes generated in the agro-food industries, and their potential applications within a circular and sustainable bioeconomy.