Thermally labile selenium peptide Arg-Asp-{Se-Met}-Pro-Ile-Gln in biofortified milk: Degradation kinetics driven by β-elimination and stabilization via cavitation-mediated structural preservation

Selenium peptides serve as an ideal dietary selenium supplement for humans. Currently, bovine milk is not much utilized as a source of selenium peptides. This study employed a full MS-dd-MS2 acquisition method to conduct selenopeptidomic analysis in selenium-biofortified bovine milk, leading to the identification of a novel selenium peptide, Arg-Asp-{Se-Met}-Pro-Ile-Gln. Structural confirmation was achieved through its molecular ion peak (error 2.28 ppm), multi-stage fragment ions, and Se-C vibrational signatures. Thermal processing induced selenium peptide Arg-Asp-{Se-Met}-Pro-Ile-Gln cleavage, significantly impacting retention efficiency. Thermal degradation rate equations for Arg-Asp-{Se-Met}-Pro-Ile-Gln were established at 63 ℃, 72 ℃, and 135 ℃, with degradation rates of 0.00368, 0.02997, and 0.0421 min^-1, respectively. Heat-induced degradation products (K₁ (C₂₂H₃₄N₅O₇Se), K₂ (C₂₂H₃₅N₅O₇Se), and {Se-Met}-Pro) were identified, revealing a dual-pathway mechanism: β-elimination-driven C-C bond cleavage at the aspartic acid carboxyl terminus and C-N bond rupture in the proline-isoleucine amide linkage. The developed thermal reaction models exhibited high accuracy (R² ≥0.9712), enabling precise quantification of real-time pyrolysis kinetics. Notably, degradation product K₂ exhibited the lowest activation energy, indicating its role as a thermal marker. The ultrasonic cavitation technique was introduced to inhibit the C-C bond cleavage rate, effectively inhibit K₂ generation, and block the cascade degradation. This study offers theoretical support for the development of selenium peptide Arg-Asp-{Se-Met}-Pro-Ile-Gln and the retention of activity in thermal processing.