Structural identification, stability and combination mechanism of calcium-chelating wheat gluten peptides

In order to explore the structures and combination mechanism of wheat gluten peptides-calcium chelate (WOP-Ca) in depth, WOP-Ca were prepared by chelating wheat gluten peptides (WOP) with calcium. The yield of WOP-Ca was determined to be 51.2 ± 2.12 %, and it exhibited a calcium-chelating rate of 58.96 ± 1.38 %. The structural differences between WOP-Ca and WOP were characterized using various analytical techniques, and the results revealed that WOP-Ca and WOP differed in their microstructure, characteristic group absorption peaks, changes in electron cloud distribution, and thermal stability. WOP-Ca demonstrated remarkable stability and resistance to changes in pH, temperature, and in vitro digestion with gastric protease. After undergoing various treatments, the molecular weight distribution in each interval changed very little. Identification of the peptides in WOP-Ca was achieved by utilizing a mass spectrometer, and a total of 39 peptides were identified in WOP-Ca. Among these, 14 peptides with Score ≥ 30 and Coverage ≥ 20 showed bioavailability percentages exceeding 30 %, with half surpassing 50 %. The binding mode between the 14 peptides and Ca2+ was determined to be α linkage. The Ca–O bond lengths ranged from 2.40 to 3.20 Å, indicating the formation of structurally stable complexes. The carboxyl oxygen atoms played a crucial role in binding with Ca2+, with bond lengths ranging from 2.41 to 2.49 Å and 2.43 to 2.46 Å, respectively. The finding suggested that WOP-Ca prepared by chelation may be used as a calcium supplement that could serve as food additives, dietary nutrients, and pharmaceutical agents.