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. 2024 Apr 4;13(7):1109.
doi: 10.3390/foods13071109.

Glycated Walnut Meal Peptide-Calcium Chelates: Preparation, Characterization, and Stability

Zilin Wang  1 , Ye Zhao  1 , Min Yang  1 , Yuanli Wang  1 , Yue Wang  1 , Chongying Shi  1 , Tianyi Dai  1 , Yifan Wang  1 , Liang Tao  1   2   3 , Yang Tian  2   3   4
Affiliations

Glycated Walnut Meal Peptide-Calcium Chelates: Preparation, Characterization, and Stability

Zilin Wang et al. Foods. .

Abstract

Finding stable and bioavailable calcium supplements is crucial for addressing calcium deficiency. In this study, glycated peptide-calcium chelates (WMPHs-COS-Ca) were prepared from walnut meal protein hydrolysates (WMPHs) and chitosan oligosaccharides (COSs) through the Maillard reaction, and the structural properties and stability of the WMPHs-COS-Ca were characterized. The results showed that WMPHs and COSs exhibited high binding affinities, with a glycation degree of 64.82%. After glycation, Asp, Lys, and Arg decreased by 2.07%, 0.46%, and 1.06%, respectively, which indicated that these three amino acids are involved in the Maillard reaction. In addition, compared with the WMPHs, the emulsifying ability and emulsion stability of the WMPHs-COS increased by 10.16 mg2/g and 52.73 min, respectively, suggesting that WMPHs-COS have better processing characteristics. After chelation with calcium ions, the calcium chelation rate of peptides with molecular weights less than 1 kDa was the highest (64.88%), and the optimized preparation conditions were 5:1 w/w for WMPH-COS/CaCl2s, with a temperature of 50 °C, a chelation time of 50 min, and a pH of 7.0. Scanning electron microscopy showed that the "bridging role" of WMPHs-COS changed to a loose structure. UV-vis spectroscopy and Fourier transform infrared spectrometry results indicated that the amino nitrogen atoms, carboxyl oxygen atoms, and carbon oxygen atoms in WMPHs-COS chelated with calcium ions, forming WMPHs-COS-Ca. Moreover, WMPHs-COS-Ca was relatively stable at high temperatures and under acidic and alkaline environmental and digestion conditions in the gastrointestinal tract, indicating that WMPHs-COS-Ca have a greater degree of bioavailability.

Keywords: glycated peptide–calcium chelates; physicochemical properties; stability; structural characterizations; walnut meal protein hydrolysates.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Effects of the WMPH/COS ratio (A), concentration of WMPHs (B), pH (C), temperature (D), and time (E) on the degree of glycation. Different letters indicate significant differences.
Figure 2
Figure 2
Response surface plots of the effects of four factors on the glycation degree. (A) Interaction between A (time) and B (concentration of WMPHs). (B) Interaction between A (time) and C (pH). (C) Interaction between A (time) and D (temperature). (D) Interaction between B (concentration of WMPHs) and C (pH). (E) Interaction between B (concentration of WMPHs) and D (temperature). (F) Interaction between C (pH) and D (temperature).
Figure 3
Figure 3
Structural and processing characteristics of the WMPHs and WMPHs–COS. (A) SDS–PAGE electrophoresis. (B) CD spectrum. (C) Protein solubility. (D) Emulsifying ability and emulsion stability. The symbols indicate statistical significance: ***: p ≤ 0.001, ****: p ≤ 0.0001.
Figure 4
Figure 4
Effects of the molecular weight of the WMPHs (A), WMPH/CaCl2 concentration (w/w) (B), pH (C), temperature (D), and time (E) on the calcium-binding capacity. Different letters indicate significant differences.
Figure 5
Figure 5
Structural characterization of WMPHs, WMPHs–COS, and WMPHs–COS–Ca. (A) UV–vis absorption spectrum. (B) FTIR spectrum. (C) Scanning electron microscopy. 1–2: WMPHs, 3–4: WMPHs–COS; 5–6: WMPHs–COS–Ca.
Figure 6
Figure 6
Stability of WMPHs–Ca and WMPHs–COS–Ca. (A) Temperature stability. (B) pH stability. (C) Simulated gastrointestinal digestion. The symbols indicate statistical significance: ns: p > 0.05, *: p < 0.05, **: p < 0.01, ***: p < 0.001, ****: p < 0.0001.
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