Food-derived protein-based calcium chelates: digestive stability, intestinal transport, and bone-related functions

Conventional calcium supplements often show limited bioaccessibility and suboptimal gastrointestinal tolerance. Food-derived proteins, protein hydrolysates, and peptide-calcium chelates have been investigated as protein-based calcium chelates. This review organizes these systems along a structural continuum from proteins to hydrolysates and peptide-calcium chelates, in which enzymatic hydrolysis, fractionation, purification, and chelation reshape carrier composition, molecular weight distribution, and calcium coordination characteristics. Within this framework, this review examines the preparation strategies, molecular features, gastrointestinal stability, intestinal transport behavior, and bone-related functions of protein-based calcium chelates. Particular attention is given to the effects of chelate type, molecular weight distribution, peptide sequence, and coordination stability on calcium retention, solubility, and transport-related behavior during digestion, as well as their links with osteogenic responses, gut microbiota changes, and the gut-bone axis. Overall, this review provides a structured framework for evaluating food-derived protein-based calcium chelates and their potential application in food-based calcium delivery systems, while highlighting future needs in functional validation, product standardization, safety assessment, and clinically relevant evidence.