The role of “unknown” hop proteins

Technical Session 04: Hops II Session
Martina Gastl, Lehrstuhl für Brau- und Getränketechnologie, Freising, Germany
Co-author(s): Christoph Neugrodda and Thomas Becker, Lehrstuhl für Brau- und Getränketechnologie, Freising, Germany

ABSTRACT: Compared to the large quantities of malt required in beer production, the amount of hops (Humulus lupulus) needed is significantly smaller. This minor ingredient has a crucial impact on beer flavor and physical properties (i.e., foam stability, turbidity). In hop research, much attention has been given to the major components: hop resins (10–30%), hop oils (0.4–2%), and hop polyphenols (4–14%). Despite the recent “boom” in hop research, hitherto, the role of hop proteins remains unknown. Besides the major components present in the dry substance of Humulus lupulus, other valuable substances are found in hops. Depending of the variety, hop proteins constitute up to 15% (w/w) of the dry matter. Although, the influence of proteins (from barley/barley malt) on beer turbidity is indisputable, to date there is no research on the characterization of hop proteins and their impact on beer turbidity and flavor. In this research, modern analytical methods available for protein research (i.e., bioanalyzer, 2D-PAGE, off-gel-fractionation) were used to characterize hop proteins based on their molecular weight and isoelectric point (pI). Further, the hop protein compositions were monitored throughout the brewing process, that is from the raw material to the finished beer. The results show significant differences in the protein composition of different hop varieties. Furthermore, these results make it possible to estimate the impact of hop proteins relative to malt proteins on beer properties.

Martina Gastl apprenticed as a brewer and maltster from 1994 to 1996 in Klosterbrauerei Andechs, Germany. She studied brewing and beverage technology at the Technische Universität München-Weihenstephan, Germany. She graduated as an engineer in 2002. From 2002 until 2006 she completed her Ph.D. concerning the “Technological Influence on Lipid Degradation in Terms of Improvement of Beer Flavor Stability.” She is currently assistant professor and head of the laboratory, as well as the raw material and beverage design research group, at the Lehrstuhl für Brau- und Getränketechnologie in Weihenstephan. Since 2008 she has been working on her post-doctoral lecture qualification. Her research interests involve characterization and interaction of flavor active taste and aroma compounds in cereal-based beverages influencing beverage harmony.