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.
Highlights
Beer flavour is determined by its chemical composition, which includes proteins and volatile flavour compounds such as esters, alcohols, fatty acids, sulphur compounds and ketones
The data were illustrated by the spider web chart (Figure 1). These results demonstrated that the vintage beer had robust flavour stability as the fresh beer
Considering the constant abundance of the 10 kDa protein in all 3 samples (Figure 2a) the results demonstrated that the disappearance of thiol groups of this protein in the aged beer was due to its oxidation
Summary
Beer flavour is determined by its chemical composition, which includes proteins and volatile flavour compounds such as esters, alcohols, fatty acids, sulphur compounds and ketones. The stability of these chemical components determines the shelf life of packaged beer. Previous studies have demonstrated that these ROS react with beer components such as polyphenols, iso-α-acids and alcohols to produce off-flavor carbonyl compounds like aldehydes and ketones [9]. The brewing industry have been attempting to maintain beer flavour stability and prolong its shelf life by minimising the oxygen content and ROS in the process of brewing using varieties of antioxidant compounds such as polyphenols, sulphites, sulphur dioxide and vitamins. (proteins) in beer could play a role in beer ageing by providing antioxidant activity we profiled the beer proteins in fresh, aged and stable vintage beers and isolated an interesting thiol-protein with antioxidant activity
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