Addition of Hop (Humulus Lupulus L.) Bitter Acids Yields Modification of Malt Protein Aggregate Profiles during Wort Boiling

Hop bitter acids are used in the brewing industry to
give beer
bitterness. However, much of this bitterness is lost during processing,
specifically during the wort boiling step. One of the major causes
might be the interaction with protein–protein complexes. Therefore,
the aim of this study was to clarify the role of hop bitter acids
in protein aggregate formation using a proteomic approach. The effect
of hop addition on protein composition was analyzed by liquid chromatography–mass
spectrometry/MS (LC-MS/MS), and further analyses were performed to
characterize the wort before and after boiling. Addition of hop bitter
acids yielded a change in wort protein profiles, and hop bitter acids
were found to bind primarily to less abundant proteins which are not
related to beer quality traits, such as foam or haze. Wort protein
aggregate profiles were revealed, and findings from this study suggested
the precipitation of particular proteins in the aggregates during
boiling when hops were added.