Identification of a protein with antioxidant activity that is important for the protection against beer ageing.
This study was carried out with fresh Australian lager beer which was sampled directly off the production line, the same samples aged for 12 weeks at 30 °C, and the vintage beer which was kept at 20 °C for 5 years. Characteristic Australian lager flavour was maintained in the fresh and vintage beers but was lost in the aged beer. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and free thiol group labelling analyses of beer proteins found that this flavour stability correlated with the presence of an unknown 10 kilodaltons (kDa) protein with a higher level of free thiols. The protein was purified by size-exclusion chromatography, then peptide sequencing and database matching identified it as the barley lipid transfer protein (LTP1). Further characterisation using diphenylpicrylhydrazyl (DPPH) free radical scavenging and a Saccharomyces cerevisiae-based antioxidant screening assay demonstrated that the LTP1 protein was active in DPPH reduction and antioxidant activity. The absence of free thiol in the aged beer indicates that the thiol functional groups within the LTP1 protein were saturated and suggests that it is important in the flavour stability of beer by maintaining reduction capacity during the ageing process.
School of Biomedical and Health Sciences, College of Health and Science, University of Western Sydney, Locked Bag 1797, Penrith South DC, New South Wales 1797, Australia; E-Mail:  p.odoherty@uws.edu.au.
Ming J
MJ
Wu
Frank M
FM
Clarke
Peter J
PJ
Rogers
Paul
P
Young
Narelle
N
Sales
Patrick J
PJ
O'Doherty
Vincent J
VJ
Higgins
D000975:Antioxidants / Q000302:isolation & purification / Q000378:metabolism* / Q000494:pharmacology; D001315:Australia; D001515:Beer / Q000032:analysis*; D001713:Biphenyl Compounds / Q000037:antagonists & inhibitors / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D061353:Food Storage; D016166:Free Radical Scavengers / Q000302:isolation & purification / Q000378:metabolism / Q000494:pharmacology; D005609:Free Radicals / Q000037:antagonists & inhibitors / Q000378:metabolism; D001467:Hordeum / Q000378:metabolism; D006801:Humans; D010851:Picrates / Q000037:antagonists & inhibitors / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D020539:Sequence Analysis, Protein; D013438:Sulfhydryl Compounds / Q000378:metabolism; D013696:Temperature; D013997:Time Factors
D000975:Antioxidants; D001713:Biphenyl Compounds; D002352:Carrier Proteins; D016166:Free Radical Scavengers; D005609:Free Radicals; D010851:Picrates; D010940:Plant Proteins; D013438:Sulfhydryl Compounds; C030363:lipid transfer protein; C004931:1,1-diphenyl-2-picrylhydrazyl