Behaviour of Antioxidants Derived from Hops During Wort Boiling

Wietstock, Philip C.; Kunz, Thomas; Shellhammer, Thomas H.; Schön, Thore; Methner, Frank‐Jürgen

doi:10.1002/j.2050-0416.2010.tb00412.x

Cited by 31 publications

(47 citation statements)

References 40 publications

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“…). These results confirm earlier investigations and point to the strong antioxidative influence of hop ingredients on the wort. Throughout the course of wort boiling, the ESR signal intensity increased again until the end of boil.…”

Section: Resultssupporting

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%

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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: Resultssupporting

confidence: 92%

Section: Discussionsupporting

confidence: 74%

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

et al. 2014

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“…Previous studies have shown that hops have a radical scavenging effect , which is most likely also the case in the current study, since wort boiling is known to increase radical formation. The additional 60 min of boiling should therefore result in an increase in radical formation . Boiling with hops resulted in a small decrease in protein content, as well as in a rather large decrease in Fe and Cu levels (Table ).…”

Section: Resultssupporting

confidence: 77%

Storage stability of pasteurized non-filtered beer

et al. 2013

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The influence of pasteurization on non-filtered beers was investigated during accelerated storage (40°C, 41 days). Two beers were produced from the same hopped wort, which was fermented with two different yeast strains. Half of the bottled beers were tunnel pasteurized resulting in four different beer samples. The pasteurization influenced the volatile profile of both fresh beers, but during storage the differences between the volatile profiles of pasteurized and non-pasteurized beers disappeared. During the storage period, the pasteurized beers gave a lower rate of radical formation, as evaluated by electron spin resonance spectroscopy, indicating a better oxidative stability. The pasteurization had no effect on the levels of the pro-oxidative metals iron and copper. Pasteurization slightly increased the protein content of the beers. SDS-PAGE analysis showed that the two beers had different protein profiles, which changed during storage; however, pasteurization of both beers did not affect their protein profiles. The level of thiols were lowered in one beer and raised in the other beer by pasteurization, but during storage the levels of thiols decreased at the same rate in all of the beers. It was concluded that pasteurization had a positive influence on the oxidative stability of non-filtered beer.

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“…Trans isomers are less stable than cis isomers 39 . The α-acids and β-acids are more potent radical quenchers than are the iso-α-acids and polyphenols 166 . Aldol condensation interactions between different carbonyl compounds can lead to different carbonyl substances 55 .…”

Section: Flavour Instabilitymentioning

confidence: 98%