Plant‐Derived Byproducts for Probiotic Encapsulation: A Composition–Microstructure–Function Review

ABSTRACT Probiotic delivery in foods is limited by viability losses during processing, storage, and gastrointestinal (GI) transit. Encapsulation may improve probiotic survival, but its effectiveness depends on both the carrier matrix and the surrounding food environment. This review examines plant‐derived byproducts, including peels, pomaces, press cakes, pulp residues, and fiber‐rich streams, as functional co‐components of probiotic carrier systems. Rather than treating these materials as generic sustainability additives, we classify them according to dominant compositional fractions, including soluble polysaccharides, insoluble fibers, resistant starch, phenolic‐rich extracts, and protein‐containing fractions. A composition–microstructure–function framework is used to evaluate how byproduct composition, processing history, matrix properties, and stress conditions influence probiotic retention, release, and survival. Reported benefits are most interpretable when supported by matched comparators and physicochemical or microstructural measurements. Semiquantitative synthesis shows that byproduct effects vary across storage and GI conditions. Stronger mechanistic attribution is possible when viability improvements are reported alongside descriptors such as water activity, particle morphology, swelling, release behavior, and structural features. Translation remains constrained by feedstock variability, inconsistent reporting, limited comparator designs, regulatory uncertainty, fractionation scalability, and sensory or consumer‐acceptance challenges. Overall, plant‐derived byproducts show promise as candidate matrix components for food‐grade probiotic delivery systems. Future progress will require safety qualification, specification‐based material selection, evidence‐weighted performance assessment, and validation in realistic food systems.