Browsing by Author "Zeng, Xin"

The literature review part describes a whey protein, ?-lactalbumin (ALA) and its oxidation, aronia (Aronia melanocarpa) procyanidins including their chemistry and analysis, as well as interactions between protein and plant phenolics. The aim of the thesis was to study the oxidation of tryptic peptides of ALA with and without procyanidins. Fractions containing both procyanidin dimers and trimers were collected from aronia juice proanthocyanidins with preparative-HPLC thereafter identified and quantified with UHPLC and NP-HPLC. ALA was digested by modified trypsin and the subsequent peptides were fractionated with preparative-HPLC. The selected peptides were WLAHKALC (m/z 936) and LDQWLCEK (m/z 1034), containing specific amino acids prone to oxidation. The oxidation of peptides with and without procyanidins was catalysed by ascorbic acid, H2O2 and FeCl3, and lasted for 14 days. Oxidation was monitored with LC-MS using samples collected on days 0, 1, 7 and 14. For peptide-phenolic interaction studies, peptide WLAHKALC (m/z 936) was incubated with procyanidin B2 standard (dimer) and peptide LDQWLCEK (m/z 1034) with aronia procyanidin dimers and trimers with a 10:1 ratio. Dimeric and trimeric procyanidins exhibited antioxidant activity towards selected peptides. Possible interaction products were not detected. For further investigations of interaction, higher concentration and ratio of peptides and procyanidins as well as expanding the MS detection range are recommended. Intensive research of oxidation products of ALA peptides is needed to accomplish a thorough understanding of the oxidation and other interaction reactions of ALA peptides with other food constituents.