Bioactivities and Functional Potential of Soy-Derived Small Peptides (2-5 Amino Acids): A Comprehensive Review

Soy-derived small peptides (SSPs, 2-5 amino acids) are food-derived bioactive peptides with efficient intestinal absorption, primarily via peptide transporter 1 (PepT1), and greater digestive stability than longer peptides. This review systematically summarizes 175 SSPs reported between 1996 and 2026, covering their production, separation, characterization, absorption mechanisms, and biological activities. SSPs are obtained mainly by controlled enzymatic hydrolysis using alcalase, thermolysin, papain, and flavourzyme, or by fermentation with Lactobacillus plantarum, Bacillus subtilis, and Aspergillus oryzae. In vitro and in vivo studies demonstrate that SSPs lower blood pressure, reduce oxidative stress and inflammation, modulate glucose and lipid metabolism, and exert anticancer and neuroprotective activities. These effects are linked to peptide sequence, hydrophobicity, Pro/Tyr enrichment, digestive stability, and transporter-mediated or paracellular transport. However, clinical evidence, dose-response data, intact systemic availability, and standardized production remain scarce. This review identifies the critical validation, scalability, and formulation gaps that must be addressed before SSPs can advance into nutraceutical and functional food applications.