Donkey milk is a valuable product for the food industry due to its nutraceutical, nutritional, and functional properties. In this work, the endogenous peptides from donkey milk were investigated for their antioxidant and ACE-inhibitory activities, combining a two-dimensional peptide fractionation strategy with high-resolution mass spectrometry, bioinformatics analysis, and in vitro assays. After extraction, the endogenous peptides were fractionated twice, first by polymeric reversed phase and then by hydrophilic interaction chromatography. Fractions were screened for the investigated bioactivities and only the most active ones were finally analyzed by nanoRP-HPLC-MS/MS; this approach allowed to reduce the total number of possible bioactive sequences. Results were further mined by in silico analysis using PeptideRanker, BioPep, and PepBank, which provided a bioactivity score to the identified peptides and matched sequences to known bioactive peptides, in order to select candidates for chemical synthesis. Thus, five peptides were prepared and then compared to the natural occurring ones, checking their retention times and fragmentation patterns in donkey milk alone and in spiked donkey milk samples. Pure peptide standards were finally in vitro tested for the specific bioactivity. In this way, two novel endogenous antioxidant peptides, namely EWFTFLKEAGQGAKDMWR and GQGAKDMWR, and two ACE-inhibitory peptides, namely REWFTFLK and MPFLKSPIVPF, were successfully validated from donkey milk.
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This work has been carried out within the framework of the Research Project “Identification and characterization of new bioactive peptides in milk and dairy products,” supported by Sapienza Università di Roma, nr. C26H15WEZH.
The MS proteomics data have been deposited to the ProteomeXchange Consortium  via the PRIDE partner repository with the dataset identifier “PXD004035.”
Conflict of interest
The authors declare that they have no competing interests.
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Zenezini Chiozzi, R., Capriotti, A.L., Cavaliere, C. et al. Purification and identification of endogenous antioxidant and ACE-inhibitory peptides from donkey milk by multidimensional liquid chromatography and nanoHPLC-high resolution mass spectrometry. Anal Bioanal Chem 408, 5657–5666 (2016). https://doi.org/10.1007/s00216-016-9672-z
- Donkey milk
- Antioxidant peptides
- ACE-inhibitory peptides
- Off-line two-dimensional chromatography
- High-resolution mass spectrometry