LC–MS investigations on interactions between isolated β-lactoglobulin peptides and lipid oxidation product malondialdehyde

Interactions between secondary lipid oxidation product malondialdehyde (MDA) and selected β-lactoglobulin (β-Lg) peptides were investigated. Selected tryptic peptides of β-Lg (ALPMHIR, LIVTQTMK and VLVLDTDYK) were fractionated via preparative-HPLC and incubated with MDA at 37 °C and 60 °C for 7 days. Changes in samples were monitored with LC-ESI-MS coupled with UV and fluorescence detectors. Prominent modifications in peptide samples included formation of two distinct types of MDA adducts observed with mass increments of 54 and 134 amu, corresponding to Schiff base and dihydropyridine (DHP)-type adducts, respectively. Modified peptides with m/z +54 amu were more stable at 37 °C than at 60 °C but showed more rapid formation than compounds with m/z +134 amu. MDA-peptide adducts resulting in +134 amu mass increment displayed strong fluorescent characteristics and they were more stable than Schiff base adducts at 60 °C.