An overview of the extraction and characterization of bioactive phenolic compounds from agri-food waste within the framework of circular bioeconomy

The recycling and revalorization of wastes from the agri-food industry (AFI) have emerged in the scientific scenario as a multidisciplinary working field in the framework of the circular bioeconomy. Residues and side materials from AFI result in a great source of raw products with increasing social and economic impact. In this regard, phenolic compounds are possibly the most relevant group of phytochemicals from AFI wastes because of their multiple healthy properties, including antioxidant, anti-inflammatory, hypolipidemic, and antibacterial activities. Among other sources, olive oil, winemaking, and fruit and vegetable juice wastes have been considered to assess their revalorization. The paper reviews the recovery and characterization of AFI waste extracts to generate by-products rich in polyphenols for chemical, nutraceutical, and food science applications. Polyphenols are recovered from AFI waste by solvent extraction with conventional and advanced techniques. The resulting extracts are complex, and the major phenolic compounds should be identified and quantified. The profiling of analytes such as proanthocyanins, curcuminoids, resveratrol derivatives, caffeic acids, and oleuropein is often performed by liquid chromatography with UV/Vis or fluorescence detection. Additionally, liquid chromatography coupled to mass spectrometry is the technique of choice for the unambiguous identification of target compounds and structural elucidation of new and unknown molecules. Complementarily, the antioxidant activity of the extracts can be determined using spectrophotometric assays.