Chelating Properties and Hydroxyl-Scavenging Activities of Hop α- and Iso-α-Acids

Wietstock, Philip C.; Shellhammer, Thomas H.

doi:10.1094/asbcj-2011-0718-01

Cited by 16 publications

(28 citation statements)

References 32 publications

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“…8), demonstrate clearly that iso-α-acids have less effect on iron reduction in comparison to the α-acids in a wort and in a beer matrix. This outcome confirms earlier findings from Wietstock et al (26,43), in which they showed that α-acids are stronger chelators than iso-α-acids. Consequently, the isomerization during wort boiling minimizes the complex formation properties of the hop acids with iron ions.…”

Section: Iron and Zinc Precipitation In Buffered Model Systemssupporting

confidence: 92%

“…The results depicted in this study clearly demonstrate the positive influence of specific hop ingredients on the oxidative stability of wort and beer. In particular, the positive influence of hop acids as described in the literature could be confirmed. It could be proven that mainly α ‐acids are responsible for the increase in oxidative beer stability and that the positive effect is presumably caused by the precipitation of pro‐oxidative acting metallic ions, such as iron, in chelate complexes with α ‐acids during wort boiling, caused by the pH drop during fermentation, or by the process of dry hopping, thereby resulting in a decreased metal content in the final beer.…”

Section: Discussionsupporting

confidence: 74%

“…This outcome confirms earlier findings from Wietstock et al . , in which they showed that α ‐acids are stronger chelators than iso‐α ‐acids. Consequently, the isomerization during wort boiling minimizes the complex formation properties of the hop acids with iron ions.…”

Section: Resultsmentioning

confidence: 99%

“…The literature indicates that α-acids possess strong antioxidative properties (26,42,43,(46)(47)(48)(49)(50). When un-isomerized α-acids were added later during the boil, they underwent a shorter isomerization time and a diminished conversion of α-acids to iso-α-acids.…”

Section: Resultsmentioning

confidence: 99%

“…The investigations demonstrated that the main mechanism by which hop acids act as antioxidants is by chelating iron and by scavenging radicals . However, newer studies using a 2‐deoxyribose oxidative degradation assay revealed that both hop α ‐ and iso‐α ‐acids are capable of suppressing radical formation by complexing iron, but are incapable of scavenging hydroxyl radicals. Other authors have claimed that the oxidative degradation of iso‐α ‐acids in beer plays a role in beer staling, but to a minor degree.…”

Section: Introductionmentioning

confidence: 99%

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Possibilities to improve the antioxidative capacity of beer by optimized hopping regimes

et al. 2014

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Different hopping regimes were evaluated to investigate the effect on the oxidative stability of wort and beer. Compared with a single hop dosage at the beginning of wort boil, it was possible to increase the concentration of α-acids in pitching wort and beer by applying incremental hop dosage, dry hopping or the use of a pre-isomerized hop product in combination with an α-acid extract, which concomitantly resulted in lower iron concentrations and an enhanced flavour stability as indicated by standard wort and beer analyses, atomic absorption spectroscopy, electron spin resonance spectroscopy and sensory analysis of fresh and force-aged beers. The functional principle of hop dosage variations is explained by saving of α-acids throughout the wort production process, which yields an increased formation and precipitation of pro-oxidative acting transition metal ions (e.g. Fe) in α-acid-complexes during the whirlpool rest and fermentation. Consequently, fewer reactive oxygen species are generated. Additional laboratory trials simulating wort cooling and beer storage in buffered model solutions proved that unisomerized α-acids are strong iron chelators and confirmed the functional principle of the applied hopping regimes. Negative effects of higher α-acid contents on fermentation performance and depletion of the zinc concentration, which is an essential nutrient for yeast, could be excluded.

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Section: Iron and Zinc Precipitation In Buffered Model Systemssupporting

confidence: 92%

Section: Discussionsupporting

confidence: 74%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Possibilities to improve the antioxidative capacity of beer by optimized hopping regimes

et al. 2014

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On the contribution of malt quality and the malting process to the formation of beer staling aldehydes: a review

et al. 2021

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Despite decades of extensive research, beer flavour instability remains a challenge for both brewing and malting industries. Malt impacts the brewing process as well as the quality of the final beer. It also affects the stability of beer flavour, as it delivers to the brewing process various compounds with the potential to compromise the desired flavour characteristics of beer. These include staling aldehydes and their precursors, such as amino acids, reducing sugars, α‐dicarbonyls and bound‐state aldehydes. In general, the content of these compounds depends on barley variety and quality, the malting regime and final malt quality. Malt that represents a low potential for beer staling, i.e. that has low values of Kolbach Index, heat load, colour, LOX activity, Strecker aldehydes, transition metal ions and high antioxidative activity, leads to beer with enhanced flavour stability. However, the consistent production of malt with the desired quality remains challenging. Approaches to achieve this include adjustment of steeping and germination conditions, allowing control of grain modification and thus, the reservoir of aldehydes precursors. Also, the application of alternative kilning technologies may reduce the applied heat load, responsible for the formation of staling aldehydes and triggering development of the oxidising free radical species. This review provides an evaluation of current knowledge on the contribution of the malting process and malt quality to the formation of beer staling aldehydes. © 2021 The Authors. Journal of the Institute of Brewing published by John Wiley & Sons Ltd on behalf of The Institute of Brewing & Distilling.

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Complexation of transition metals by chelators added during mashing and impact on beer stability

et al. 2021

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Beer inevitably changes due to an array of staling reactions. A major factor in beer ageing is the involvement of transition metals (iron, copper, manganese) in oxidative reactions. To tackle the flavour stability issue, metal chelation was investigated. Based on previous research, five primary chelators (tannic acid, gallic acid, EDTA, citric acid and phytic acid) were screened using experimental design for their capacity to reduce the content of wort transition metals. The chelating agents were added under varying conditions (mash out temperature, mash pH, grain bill, chelator concentration, addition time) during laboratory scale mashing to assess how they altered complexation and metal load. Fourteen alternative chelators (ferulic acid, tartaric acid, quercetin, chlorogenic acid and ten polyphenolic food extracts: green tea, pomegranate, grape seed, reishi, cinnamon, curcuma, milk thistle, ginkgo, grapefruit seed and raspberry) were also explored. Metal ions were analysed using inductively coupled plasma optical emission spectrometry and wort oxidative stability by electron spin resonance spectroscopy. Mash pH was the most decisive of all tested process variables: acidified mashing (pH 6 to 5) produced worts with more iron, manganese and zinc (230, 320 and 150%, respectively). Addition of effective chelators counteracted this undesirable effect for iron. Green tea extract, tannic acid and, particularly, pomegranate extract all resulted in lower wort iron. Conversely, addition of EDTA, caused iron, manganese and zinc to increase. Pomegranate extract (90% ellagic acid) was the best performing chelator and reduced radical generation in wort (80% reduction by 60 mg/L addition), making it a promising novel compound in the improvement of beer shelf life.

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Chelating Properties and Hydroxyl-Scavenging Activities of Hop α- and Iso-α-Acids

Cited by 16 publications

References 32 publications

Possibilities to improve the antioxidative capacity of beer by optimized hopping regimes

Possibilities to improve the antioxidative capacity of beer by optimized hopping regimes

On the contribution of malt quality and the malting process to the formation of beer staling aldehydes: a review

Complexation of transition metals by chelators added during mashing and impact on beer stability

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