Site-Specific Formation of Maillard, Oxidation, and Condensation Products from Whey Proteins during Reaction with Lactose

Abstract

Heat treatment of dairy products leads to structural changes of proteins, which can severely decrease the nutritional value [Mauron, J. J. Nutr. Sci. Vitaminol. (Tokyo) 1990, 36 (Suppl. 1), S57-69]. In this study, model solutions of the two main whey proteins, alpha-lactalbumin and beta-lactoglobulin, respectively, were incubated with lactose, and modifications were monitored by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Lactulosyl residues were the most abundant modifications of alpha-lactalbumin and beta-lactoglobulin. Up to four of these adducts were identified on the proteins. Enzymatical digest with endoproteinase AspN prior to mass spectrometric analysis allowed the detection of further modifications and their localization in the amino acid sequence. Most prominent modifications were lactulosyllysine, Nepsilon-carboxymethyllysine, oxidation of lysine to aminoadipic semialdehyde, oxidation of methionine to methionine sulfoxide, cyclization of N-terminal glutamic acid to a pyrrolidone, and oxidation of cysteine or tryptophan. The presence of methionine oxidation was deduced from a control protein that had been oxidized by hydrogen peroxide. These studies establish MALDI-TOF-MS as a reliable tool to monitor chemical modifications of nutritional proteins during food processing.

Assessment of heat treatment of dairy products by MALDI‐TOF‐MS

“…The presence of lactulosyllysine on a protein can be deduced by the mass difference in the deconvoluted mass spectrum. MALDI-TOF-MS has been used successfully to analyze the protein profile of milk or to detect lactosylation of whey proteins in milk models [8,26]. When applied after partial enzymatic digestion, MALDI-TOF-MS can be efficiently used to analyze structure and binding site of protein modifications formed during the heat treatment of milk [7,25].…”

“…During prolonged heating, further glycation products can be formed such as N e -carboxymethyllysine, oxalic acid monolysinylamide, pyrraline, or pentosidine [3][4][5][6]. Furthermore, heating in the presence of lactose can induce protein oxidation leading to the formation of methionine sulfoxide, aminoadipic semialdehyde, or dityrosine [7][8][9][10]. Finally, protein modifications can occur, which are formed independently from the presence of lactose, such as lysinoalanine, histidinoalanine, N-terminal pyrrolidone, or partial protein hydrolysis [11][12][13].…”

Analysis of carbohydrates and glycoconjugates by matrix‐assisted laser desorption/ionization mass spectrometry: An update for 2007–2008

“…Site-specific formation of Maillard, oxidation, and condensation products from whey proteins (Meltretter, et al, 2007) α-Lacalbumin, β-lactoglobulin Lactose TOF, ESI Detection of glycated and oxidized products in whey proteins from milk (Meltretter & Pischetsrieder, 2008) α-and β-lactoglobulin and IgG Xylobiose maltose TOF (sinapinic)…”

Mass spectrometric characterization of glycated β-lactoglobulin peptides derived from galacto-oligosaccharides surviving the in vitro gastrointestinal digestion

“…The power of mass spectrometric techniques for the study of glycated and nonglycated peptides has been widely demonstrated [14,15]. Matrix-assisted laser desorption ionization (MALDI) and electrospray ionization (ESI) have been used to determine the structure of proteins and peptides and their glycation products with monosaccharides [14,16,17].…”