title: Quantification of radicals formed during heating of β-lactoglobulin with glucose in aqueous ethanol.
abstract: Heating β-lactoglobulin alone, or in the presence of glucose, at moderately elevated temperatures (50, 70 and 80°C) in 30% aqueous ethanol at pH 6.0, 7.0 and 8.0 led to an iron catalysed formation of highly reactive radicals at concentrations of up to 1.0 mmol/mol protein as trapped by α-(4-pyridyl N-oxide)-N-tert-butylnitrone (POBN) and quantified by ESR spectroscopy. Oxidation of β-lactoglobulin was favoured by increasing temperature and high pH conditions, whereas presence of glucose decreased oxidation, indicating that oxidation of β-lactoglobulin involves either amine or thiol side chain group blocked as oxidation substrate by reaction with glucose as a reducing sugar. The oxidation of β-lactoglobulin was hampered by the phenolic antioxidant 4-methylcatechol and to an even larger extent by the oxidised quinone form 4-methyl-1,2-benzoquinone, suggesting that it is the quinone forms of phenolic antioxidants which compete with reducing sugars in protecting proteins against oxidation.
authors.affiliation: Food Chemistry, Department of Food Science, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark.
authors.forename: Rikke V
authors.initials: RV
authors.lastname: Hedegaard
authors.affiliation: Food Chemistry, Department of Food Science, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark; The College of Food Science, Shenyang Agricultural University, Dongling Street No.120, Shenyang, China.
authors.forename: Ling
authors.initials: L
authors.lastname: Liu
authors.affiliation: Food Chemistry, Department of Food Science, University of Copenhagen, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark. Electronic address: ls@life.ku.dk.
authors.forename: Leif H
authors.initials: LH
authors.lastname: Skibsted
mesh_terms: D000431:Ethanol / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry*; D005947:Glucose / Q000737:chemistry*; D007782:Lactoglobulins / Q000737:chemistry*; D015416:Maillard Reaction; D010084:Oxidation-Reduction; D019097:Spin Trapping
chemical_list: D005609:Free Radicals; D007782:Lactoglobulins; D000431:Ethanol; D005947:Glucose
keywords: ESR; Intermediary radicals; Maillard reactions; Phenolic antioxidants; Protein oxidation; Spin trapping