Preparation and characterization of a novel walnut peptide–calcium chelate and its role in promoting calcium absorption in calcium-deficient mice

Walnut peptide (WP) was chelated with calcium (Ca) to prepare WP-Ca chelate. The characterization, stability, and absorption properties of WP-Ca were investigated. Results showed that WP showed a calcium-binding capacity of 14.22 μg/mg, primarily through interactions with nitrogen and oxygen atoms. WP-Ca had good thermal stability and gastrointestinal digestive stability. In the flipped rat intestinal capsule model, the calcium absorption capacity of WP-Ca increased by approximately 3.75 times, and at the same time enhanced the calcium transport of the Caco-2 cell monolayer. Additionally, the results of animal experiments on calcium deficiency induced by a low-calcium diet indicated that WP-Ca (66.67 mg Ca/kg bw) supplementation effectively corrected calcium imbalance, significantly (P < 0.05) increased trabecular number and cortical thickness, and improved skeletal mechanical strength. Pearson's correlation analysis showed that the microbial genera of Bacteroidete, Akkermansia, Allobaculum, and Oscillospira were significantly (P < 0.05) associated with increased bone mass. Overall, these findings suggest that WP-Ca shows great potential in the development of new and highly efficient calcium supplements for osteoporosis prevention, nutritional fortification for special populations, and innovation in functional foods.