Phytochemical Engineering of Alternative Plant Proteins for Enhanced Nutrition and Digestibility

Global protein security is increasingly challenged by the growing demand for sustainable alternatives to animal-derived proteins. Although plant proteins are central to this transition, they remain limited by imbalanced amino acid profiles, reduced digestibility, and inferior techno-functional properties, restricting their nutritional equivalence. Recent studies have explored processing strategies to address these limitations; however, these approaches are often evaluated independently, with limited integration of structural mechanisms and phytochemical-protein interactions. This review presents a comparative and mechanistic synthesis based on cross-study evaluation, integrating protein structure, processing-induced modifications, and phytochemical-assisted interactions. Processing strategies including extrusion, fermentation, enzymatic hydrolysis, and pH shifting primarily enhance protein accessibility and reduce antinutritional constraints. In contrast, phytochemicals modulate protein conformation and interfacial behavior through both non-covalent and covalent interactions. Evidence across studies indicates that these effects are strongly concentration-dependent: moderate phytochemical interactions promote partial unfolding and improved functionality, whereas excessive interactions induce aggregation and reduce digestibility. Notably, the combined application of bioprocessing and phytochemical strategies yields greater improvements in solubility, emulsification, and bioavailability than individual approaches, although variability in protein source and processing conditions remains a key limitation. Overall, this review establishes a mechanistic framework linking protein structure, processing dynamics, and phytochemical interactions, highlighting concentration-dependent effects and synergistic strategies for improving plant protein functionality, while identifying variability and optimization challenges for future applications.