Impacts of Copper, Iron, and Manganese Metal Ions on the EPR Assessment of Beer Oxidative Stability

Effect of dry hopping on the oxidative stability of beer

Electron spin resonance (ESR) spectroscopy was used todeterminethe effect of dry hopping on the oxidative stability and antioxidative potential of beer.Commercial beerwasdry-hopped at 5 °C and 20 °Cwith six hop varieties (Polish and American). The rate of radical formation and lag time were found to depend on the variety of hop used. An increase in the lag time and a decrease in the rate of radical formation occurred when dry-hopping was performed at 20 °C for all hop varieties (at 5 °C in some varieties). The lag time had a strong correlation with the TPC (total polyphenols content) in beer. The rate of radical formation was correlated with the iron content of the beer. A decrease in iron concentration was observed after dry-hopping at 20 °C. Overall, the evaluation of free radical formation using ESR is useful for predicting oxidative changes in beer during storage.

Copper Binding in Sweet Worts Made from Specialty Malts

Trace levels of copper can impact the flavor stability of beer. The main source of copper is malt, and the wort copper levels are established during mashing and lautering. This study focuses on sweet worts made from experimental roasted and caramel malts. Potentiometric titrations using ion-selective electrodes combined with electron paramagnetic resonance spectroscopy have been used to investigate Cu(II) binding in worts as well as the impact of Cu(II) ions on the wort oxidative stability. High-temperature treatment during malting decreased Cu(II) binding affinities in the worts, with roasted malt worts having lower affinities than caramel malt worts of similar color and pH. Electron paramagnetic resonance spectra indicated dipeptides as the main Cu(II) chelators. A positive correlation between Cu and free amino nitrogen levels in worts is demonstrated. In dark worts with high rates of radical formation, Cu(II) had pronounced antioxidative effects. In contrast, moderate prooxidative effects were observed when adding Cu(II) to pale worts with inherently low rates of oxidation.

Impact of copper-based fungicides on the antioxidant quality of ethanolic hop extracts

Hops contain a variety of compounds possessing antioxidant capacity including phenolic and polyphenolic compounds as well as α- and β- acids. These compounds may contribute to the oxidative stability of beer during brewing and storage. Hop plants may be treated with copper-based fungicides (CBFs) which have been shown to increase the total copper content of harvested hop cones; however, copper ions are well known to catalyze the generation of reactive oxygen species production in beer and may negatively impact its oxidative stability. Increased copper content in CBF-treated hops has been previously shown to have deleterious effects on the aroma quality of hops and beer. The impact of CBFs on the antioxidant content and quality of hops has not been previously investigated. In this study, ethanolic extracts of CBF-treated hops are evaluated for their metal content and antioxidant quality in order to determine whether excess copper from CBF treatment negatively impacts their antioxidant capacity.

Forensic determination of hair deposition time in crime scenes using electron paramagnetic resonance

Several types of biological samples, including hair strands, are found at crime scenes. Apart from the identification of the value and the contributor of the probative evidence, it is important to prove that the time of shedding of hair belonging to a suspect or victim matches the crime window. To this end, to estimate the ex vivo aging of hair, we evaluated time-dependent changes in melanin-derived free radicals in blond, brown, and black hairs by using electron paramagnetic resonance spectroscopy (EPR). Hair strands aged under controlled conditions (humidity 40%, temperature 20-22°C, indirect light, with 12/12 hour of light/darkness cycles) showed a time-dependent decay of melanin-derived radicals. The half-life of eumelanin-derived radicals in hair under our experimental settings was estimated at 22 ± 2 days whereas that of pheomelanin was about 2 days suggesting better stabilization of unpaired electrons by eumelanin. Taken together, this study provides a reference for future forensic studies on determination of degradation of shed hair in a crime scene by following eumelanin radicals by utilizing the non-invasive, non-destructive, and highly specific EPR technique.

Impact of Copper Fungicide Use in Hop Production on the Total Metal Content and Stability of Wort and Dry-Hopped Beer

Transition metals, including copper, iron, and manganese, are known to catalyze the generation of reactive oxygen species (ROS) in beer leading to reduced product stability. Metals in beer are generally derived from raw ingredients. The present study aims to evaluate the impact of brewing and dry-hopping using hops treated with copper-based fungicides (CBFs) on the final transition metal content of model buffer solutions and pilot-scale systems of wort and beer. Copper levels in model wort and beer solutions were elevated (105.6% and 230.4% increase, respectively) when CBF-treated hops were used. In laboratory-prepared wort, elevated copper concentrations were not observed when CBF-treated hops were used for boiling. Dry hopping of beer using CBF-treated hops led to significant increases in total copper content (ca. 75 µg/kg vs. ca. 40–50 µg/kg in the control-hopped beer) when yeast was absent from the treated beer, but not when yeast was present. It was observed that manganese levels were significantly elevated in all hopped beers (ca. 495–550 µg/kg vs. 90–125 µg/kg in the unhopped control), regardless of hop treatment. A hop varietal thiol, 4-Mercapto-4-methylpentan-2-one, was spiked into treated beers, and the rate of oxidative loss was monitored during aging. Rates of thiol loss in treated beer samples did not differ across CBF treatments but were significantly lower in unhopped controls in the absence of yeast (p < 0.0001) and correlated significantly with total manganese content of the beers (R2 = 0.4228, p = 0.0006). The rate of staling in hopped beers as measured by the rate of 1-hydroxyethyl radical generation did not differ among hop treatments, suggesting that excess copper content contributed from the hops does not negatively impact the oxidative stability of the beers. These findings suggest that brewers can use CBF-treated hops without any negative implications for the shelf stability of their beers and do not contraindicate the use of CBF in hops production when necessary.

A Review of the Potential Health Benefits of Low Alcohol and Alcohol-Free Beer: Effects of Ingredients and Craft Brewing Processes on Potentially Bioactive Metabolites

Beer is a beverage of significant historical and cultural importance. Interest in the potential health effects of alcoholic beverages has largely focused on wine; however, there are a number of potentially beneficial bioactives that beer may contain that warrant further investigation. The challenge of considering any potential health benefits of beer are restricted by the negative consequences of its alcohol and energy content. There is potential to enhance the bioactive qualities of beer whilst reducing the alcohol and energy content through novel brewing approaches often used in craft brewing, in terms of ingredients, brewing methods and type of fermentation. Consumer demand to produce a greater variety of beer types, including alcohol-free beers, may also help to increase the number of beers which may have greater potential to improve health, with lower levels of alcohol, while still being tasty products. As low alcohol, prebiotic and bioactive containing beers are developed, it is important that their potential health benefits and risks are fully assessed.