Natural Pigment Recovery from Agri-Food Residues: A Critical Review of Extraction Approaches and Food Applications

The extraction of natural pigments from plant-based food by-products represents a promising approach for waste utilisation and the development of sustainable food ingredients. Agricultural and food industry residues, including peels, pomace, and various other processing by-products, are rich in bioactive pigments including anthocyanins, betalains, carotenoids, and chlorophylls. These pigments can be used as natural colouring agents and also offer extra functional advantages. This overview brings together the recent literature from Web of Science and Scopus on methods commonly described as green or sustainable extraction approaches for plant-based food by-products. After applying the predefined eligibility criteria, 45 peer-reviewed original research articles that were published between January 2015 and April 2026 were included in the final analysis. The studies selected were compared according to the raw material, type of pigment, extraction technique, processing conditions, analytical methods, and the extraction performance that was reported. When specific experimental conditions are considered, green extraction methods such as ultrasound-assisted, microwave-assisted, enzyme-assisted, and supercritical fluid extraction often show benefits in terms of pigment recovery, extraction time, or solvent use. Yet direct comparisons are difficult because of the large differences in the plant matrices, the characteristics of the pigments, the extraction parameters, the reference methods, and the units in which the results are reported. As a result, no one extraction technology consistently performs better than the others for all types of pigments and all by-product matrices. The extraction performance is greatly affected by the polarity of the pigment, the composition of the matrix, the solvent system, and the processing conditions. New solvent systems, for example, natural deep eutectic solvents, also have potential, but more evidence is needed regarding their suitability for food applications, their recovery rates, their scalability, and their acceptance by regulatory authorities. In short, plant-based food by-products are a valuable source of natural pigments, and green extraction technologies offer feasible ways to improve pigment recovery. The choice of an extraction method should be based on the particular characteristics of the target pigment and matrix, rather than assuming that any one technology is generally superior. More research is needed in order to improve process standardisation, enhance the comparability of studies, carry out scale-up, and move towards industrial food applications.