Phenolic Substances in Beer: Structural Diversity, Reactive Potential and Relevance for Brewing Process and Beer Quality

Abstract

For the past 100 years, polyphenol research has played a central role in brewing science. The class of phenolic substances comprises simple compounds built of 1 phenolic group as well as monomeric and oligomeric flavonoid compounds. As potential anti-or prooxidants, flavor precursors, flavoring agents and as interaction partners with other beer constituents, they influence important beer quality characteristics: flavor, color, colloidal, and flavor stability. The reactive potential of polyphenols is defined by their basic chemical structure, hydroxylation and substitution patterns and degree of polymerization. The quantitative and qualitative profile of phenolic substances in beer is determined by raw material choice. During the malting and brewing process, phenolic compounds undergo changes as they are extracted or enzymatically released, are subjected to heat-induced chemical reactions or are precipitated with or adsorbed to hot and cold trub, yeast cells and stabilization agents. This review presents the current state of knowledge of the composition of phenolic compounds in beer and brewing raw materials with a special focus on their fate from raw materials throughout the malting and brewing process to the final beer. Due to high-performance analytical techniques, new insights have been gained on the structure and function of phenolic substance groups, which have hitherto received little attention. This paper presents important information and current studies on the potential of phenolics to interact with other beer constituents and thus influence quality parameters. The structural features which determine the reactive potential of phenolic substances are discussed.

Technological influence on sensory stability and antioxidant activity of beers measured by ORAC and FRAP

“…No significant differences were observed between the beers hopped at the beginning of wort boiling with CO 2 extract or type 90 pellets, even though hop phenolic ingress is higher for pellet dosage . However, with an early hop dosage and therefore longer hop boiling times there is also a greater depletion of hop phenolic compounds . The whirlpool‐hopped beers had a significantly higher antioxidant potential (Table ).…”

“…Both brewing raw materials are rich in antioxidants. Barley ( Hordeum vulgare L.) contains a variety of phenolic compounds: Benzoic and cinnamic acid derivatives, hordatines, lignans and flavonoids . During malting, the phenolic content of grain extracts increases due to the enzymatic release of phenolic acids from cell‐wall polysaccharides and due to the enhanced extractability of the malted grain .…”

“…The phenolic content of malted barley depends on the malting regime, with higher levels of malt modification resulting in a higher content of free phenolic acids . There is a myriad of antioxidant compounds derived from hops ( Humulus lupulus L.): Resinous compounds like α ‐acids or prenylated chalcones and non‐resin phenolic compounds like phenolic acids or flavonoids . Hop is either added at the beginning of wort boiling to achieve the desired bitterness or at the end of boiling or during whirlpool rest to impart a hoppy aroma to the final beer .…”

“…1 Antioxidants in beer have therefore been of great interest to brewers due to their beneficial role in beer storage stability. [2][3][4] The antioxidant compounds of beer are heterogeneous, belonging to completely different chemical substance groups: Sulfur dioxide, 3,5,6 thiols, 7 Maillard reaction products, 8,9 hop-derived bitter compounds like -acids [10][11][12] and phenolic substances [13][14][15][16][17] from both barley malt and hops. Both brewing raw materials are rich in antioxidants.…”

“…Barley (Hordeum vulgare L.) contains a variety of phenolic compounds: Benzoic and cinnamic acid derivatives, hordatines, lignans and flavonoids. 13,[18][19][20][21] During malting, the phenolic content of grain extracts increases due to the enzymatic release of phenolic acids from cell-wall polysaccharides and due to the enhanced extractability of the malted grain. [22][23][24] As recent studies have shown, the antioxidant activity of malt is correlated with the antioxidant activity of the raw barley, which is influenced by genotype and growth factors.…”