title: MALDI-TOF MS characterization of glycation products of whey proteins in a glucose/galactose model system and lactose-free milk.
abstract: The major modifications induced by thermal treatment of whey proteins α-lactalbumin (α-La) and β-lactoglobulin (β-Lg) in a model system mimicking lactose-free milk (L(-) sugar mix) were investigated by matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS). The analysis of the intact α-La revealed species with up to 7 and 14 adducts from lactose and sugar mix, respectively, whereas for β-Lg 3 and up to 5 sugar moieties were observed in the case of lactose and sugar mix experiments, respectively. A partial enzymatic hydrolysis with endoproteinase AspN prior to mass spectrometric analysis allowed the detection of further modifications and their localization in the amino acid sequence. Using α-cyano-4-chlorocinnamic acid as MALDI matrix, it could be shown that heating α-La and β-Lg with glucose or galactose led to the modification of lysine residues that are not glycated by lactose. The higher glycation degree of whey proteins in a lactose-free milk system relative to normal milk with lactose reflects the higher reactivity of monosaccharides compared to the parent disaccharide. Finally, the analysis of the whey extract of a commercial lactose-free milk sample revealed that the two whey proteins were present as three main forms (native, single, and double hexose adducts).
authors.affiliation: Dipartimento di Chimica and Centro di Ricerca Interdipartimentale S.M.A.R.T. Università degli Studi di Bari Aldo Moro, Via Orabona 4, 70126 Bari, Italy. Saverio.Carulli@agenziadogane.it
authors.forename: Saverio
authors.initials: S
authors.lastname: Carulli
authors.forename: Cosima D
authors.initials: CD
authors.lastname: Calvano
authors.forename: Francesco
authors.initials: F
authors.lastname: Palmisano
authors.forename: Monika
authors.initials: M
authors.lastname: Pischetsrieder
mesh_terms: D000818:Animals; D005690:Galactose / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D006031:Glycosylation; D006358:Hot Temperature; D007768:Lactalbumin / Q000737:chemistry / Q000378:metabolism; D007782:Lactoglobulins / Q000737:chemistry / Q000378:metabolism; D007785:Lactose / Q000032:analysis* / Q000378:metabolism; D008666:Metalloendopeptidases / Q000378:metabolism; D008892:Milk / Q000737:chemistry*; D008894:Milk Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D010084:Oxidation-Reduction; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D000067816:Whey Proteins
chemical_list: D007782:Lactoglobulins; D008894:Milk Proteins; D000067816:Whey Proteins; D007768:Lactalbumin; D008666:Metalloendopeptidases; C058921:endoproteinase Asp-N; D005947:Glucose; D007785:Lactose; D005690:Galactose