Cysteine-Rich Peptides in Food Systems: Structure, Sources, Functional Properties, Potential Applications, and Future Perspectives.

Cysteine-rich peptides (CRPs) are structurally diverse bioactive peptides in which cysteine residues form disulfide bonds or, in some lanthipeptides, cysteine-derived thioether bridges. These constraints can improve resistance to thermal, chemical, and enzymatic stress, although stability and activity remain peptide- and matrix-dependent. CRPs have attracted interest as antimicrobial, antioxidant, and immunomodulatory agents in food preservation, functional foods, and active packaging. Nisin provides the clearest regulatory and commercial precedent: this lanthipeptide is used in selected food categories to control susceptible Gram-positive pathogens and spoilage organisms. Evidence for most plant defensins, cyclotides, and engineered CRPs, however, remains based on in vitro, preclinical, or food-model studies. This review examines CRP structures, sources, functional properties, potential food applications, and regulatory considerations. It also evaluates quantitative efficacy data, manufacturing and delivery constraints, allergenicity and toxicity, possible resistance, and the need for matrix-specific validation. CRPs should therefore be considered candidate components of validated preservation and delivery strategies rather than universal replacements for conventional additives.