title: Identification of isopeptide bonds in heat-treated wheat gluten peptides.
abstract: Results in this paper confirm heat-induced isopeptide bond formation in wheat gluten. Heating (24 h, 130 °C) of wheat gluten [moisture content 7.4%] decreased its extractability in sodium dodecyl sulfate containing buffer (pH 6.8), even after reduction of disulfide (SS) bonds. Thus, both SS bonds and non-SS bonds were responsible for the extractability loss. Cross-links of the lysinoalanine and lanthionine type were not present in the heated samples, but heat treatment reduced levels of available amino groups. Heating of purified and alkylated high molecular weight glutenin subunits (HMW-GS) under similar conditions also resulted in extractability loss, demonstrating that cross-linking did not solely depend on the availability of cysteine or cystine. These observations indicated that heat treatment had induced isopeptide bond formation, resulting in larger and unextractable molecules. Heating HMW-GS lysine- and glutamine-containing peptides induced the formation of isopeptide bonds, thereby supporting the above hypothesis. The level of isopeptide bond formation increased with heating time.
authors.affiliation: Laboratory of Food Chemistry and Biochemistry and Leuven Food Science and Nutrition Research Centre (LFoRCe), Katholieke Universiteit Leuven, Kasteelpark Arenberg 20, Box 2463, B-3001 Leuven, Belgium. Ine.Rombouts@biw.kuleuven.be
authors.forename: Ine
authors.initials: I
authors.lastname: Rombouts
authors.forename: Bert
authors.initials: B
authors.lastname: Lagrain
authors.forename: Markus
authors.initials: M
authors.lastname: Brunnbauer
authors.forename: Peter
authors.initials: P
authors.lastname: Koehler
authors.forename: Kristof
authors.initials: K
authors.lastname: Brijs
authors.forename: Jan A
authors.initials: JA
authors.lastname: Delcour
mesh_terms: D000478:Alkylation; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D003432:Cross-Linking Reagents; D004220:Disulfides / Q000737:chemistry; D005524:Food Technology; D005983:Glutens / Q000737:chemistry*; D006358:Hot Temperature; D008970:Molecular Weight; D010455:Peptides / Q000737:chemistry*; D021122:Protein Subunits / Q000737:chemistry; D014908:Triticum / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D003432:Cross-Linking Reagents; D004220:Disulfides; D010455:Peptides; D021122:Protein Subunits; D005983:Glutens; C037302:glutenin