Identification of a Protein with Antioxidant Activity that is Important for the Protection against Beer Ageing

Abstract

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.

Mini-review: The role of redox in Dopa-mediated marine adhesion

“…Redox exchange between DPPH and a broad range of mono- and polyphenolic compounds has already been demonstrated (Villano et al 2007). However, the details involving DPPH and thiol/thiolate groups of biomolecules are largely unexplored (Wu et al 2011). …”

125thAnniversary Review: The role of proteins in beer redox stability

“…Typically fresh beer contains many reduced protein thiols (PrSH), meaning that these proteins, in our vernacular, are in a reduced (redox) state . However they are lost as beer ages.…”

“…An obvious feature of the beer proteome is the dominant presence of two families of proteins, the serine protease inhibitor (serpin) family, which includes protein Z, and the lipid transfer family (LTP), both of which are derived from barley. Their abundance is more evident in one‐dimensional polyacrylamide gel electrophoresis . In addition there are up to 20 barley proteins and 40 yeast proteins .…”

Effect of Maillard reaction on reducing power of malts and beers

“…In addition to the melanoproteins, pure proteins in beer can also exhibit AOA. Wu et al (2011) found the barley lipid transfer protein with a higher level of thiol groups maintaining the reducing power during the beer ageing process. The formation of EA melanoidins occurred also during boiling, fermentation, and chill-lagering, as documented by a lower proportion of high-molecular fraction in a wort sample (13% EC) in comparison to that of the corresponding lager (19% EC).…”