From waste to structure: valorisation of agro-industrial byproducts as functional inducers of low-methoxyl pectin gelation.

Low-methoxyl (LM) and amidated low-methoxyl (LMA) pectins are widely used as calcium-responsive hydrocolloids in reduced-sugar foods and edible materials. However, their gelation still relies largely on purified calcium salts and refined co-solutes, while the structuring potential of agro-industrial side streams remains poorly integrated within a unified mechanistic framework. This review proposed that these streams should be understood as multifunctional gelation inducers, co-inducers, or modifiers whose effects arise from their mineral, sugar, organic-acid, protein, polyphenol, and polysaccharide composition. Their functionality is examined through four principal mechanisms: ion donation and competition, regulation of pH and ionic strength, control of water activity and molecular crowding, and promotion of secondary interactions or co-gelation. Evidence from rheology, spectroscopy, microscopy, and molecular modelling is integrated to connect side-stream composition and processing history with junction-zone formation, network heterogeneity, viscoelasticity, water retention, and product performance. The review further examined how these composition-structure-property relationships can guide the selection and standardisation of molasses, vinasse, whey permeate, fruit-pomace extracts, and related streams for food structuring. Gelation performance is subsequently connected with safety, sensory acceptability, process scalability, life-cycle assessment, and techno-economic feasibility. This mechanism-driven framework will provide a basis for moving from empirical side-stream incorporation towards predictive formulation strategies for multifunctional and potentially lower-impact LM/LMA pectin systems.