Flaxseed (Linum usitatissimum L.) protein and peptide identification of raw and roasted seeds: application of the UHPLC-Q-TOF-MS/MS method

Background: Flax (Linum usitatissimum L.) seeds are in the spotlight due to their enormous potential as a functional food ingredient, and proteins and peptides play a crucial role in their functional food properties. Flax seeds can be added to foods during production either before or after heat pre-treatment (roasting), creating the need for thermally stable peptides as markers for flax seed identification. In this study, the proteins of untreated and roasted seeds of three flax cultivars (Jantarol, Oliwin and Szafir) were analyzed by high-resolution tandem mass spectrometry coupled to high-performance liquid chromatography (UHPLC-Q-TOF-MS/MS) to search for species-specific peptides as potential markers of flax seeds. Results: Twenty-three proteins found in untreated seeds of each cultivar were selected using UHPLC-Q-TOF-MS/MS. After roasting, six of them were identified based on 13 unique and species-specific peptides, and they have been suggested as potential thermally stable species-specific markers for the identification of flax seed proteins. Among them, one new unique and thermally stable peptide, DPVLAWR, was found that had not been identified in previous studies. Conclusion: Our research has provided novel information on the protein and peptide identification of flax seeds taking into account possible cultivar diversity. In the study, the proteomics UHPLC-Q-TOF-MS/MS method was applied. In addition, heat-stable peptides were determined as a potential indicator for the identification of flax seeds after roasting, a process often used for oilseed pre-treatment.