Sustainable processing of agri-food by-products into food ingredients: an integrated review from pre-treatment to formulation

Agri-food processing by-products are increasingly recognized as compositionally rich feedstocks for value-added food ingredients, yet their practical valorization remains constrained by feedstock heterogeneity, moisture sensitivity, variable processability, and the difficulty of translating laboratory-scale gains into scalable ingredient pathways. Building on emerging integrative perspectives in agri-food by-product valorization, this review reorganizes evidence from pre-treatment and green extraction through downstream recovery, fractionation, and concentration to formulation, developing a comparative synthesis intended to support first-pass route selection. Rather than treating these stages as isolated technical steps, the literature is interpreted in terms of cross-stage compatibility, intermediate-stream properties, downstream burden, and the route logic shaping ingredient production. From this comparative framing, six recurring route classes are identified: whole-stream ingredient routes, clarified hydrophilic extract powder routes, polysaccharide and fiber fractionation routes, bioactive encapsulated powder routes, lipophilic extract dispersion or emulsion-filled powder routes, and purified ingredient routes. No route class is universally superior. In screening terms, lower-burden whole-stream and clarified hydrophilic extract powder routes are generally more defensible when broad ingredient functionality, handling stability, and moderate specification control are sufficient, whereas fractionation, encapsulation, dispersion, and purification routes become more defensible only when functional specificity, protection, dispersibility, or purity clearly offset their added downstream burden. Industrial relevance and sustainability are therefore better assessed at the pathway level than inferred from extraction-stage performance alone. Overall, the synthesis suggests that industrially relevant and sustainable route selection depends less on maximizing extraction-stage performance than on matching route class with ingredient-format goals, downstream requirements, and scale-up constraints.