Evaluation of copper content in beers obtained from retail in Sweden

A quantitative study of copper (Cu) content in 19 different beer brands produced in mainly European countries and consumed in Sweden were measured using atomic absorption spectrophotometer without sample digestion. Results showed that the Cu content in beers is below the permissible levels concentrations for potable drinking water recommended by World Health Organization. In addition, the studies indicated that there is no correlation between the amount of Cu content in beers and their respective hops Cu content.


INTRODUCTION
Beer is a popular beverage that is widely consumed all over the world with thousands of years of tradition.The consumption increased also in countries where there is no traditional consumption (Svendsen and Lund, 2000).Beer is produced with a range of ingredients of which the most typical are water, malted barley (and/or other malted or unmalted cereals), hops and yeast.All these ingredients are endogenous sources of metals in beer, one in particular is Cu (Hardwick, 1994).Copper content is an important ingredient during the brewing process since it is essential for many malt enzymes and yeast growth (Krofta et al., 2012).Regarding quality, positive effects of Cu on beer has been attributed to foaming quality and flavour enhancement (Pohl, 2008).Copper content also has a negative effect on beer quality as it can be involved in the formation of colloidal hazes.Furthermore, oxidation products which are linked to the presence of oxygen and metal ions such as Cu and Fe can affect the final flavour of the beer (Pohl, 2008).However, Cu is toxic in higher concentrations (Pettersson and Rasmussen, 1999).For human consumption, the need for different trace metals is stipulated by the World Health Organization (WHO, 1996) and a moderate consumption of beer can contribute to the intake of Cu (Pohl, 2008;Olivares et al., 1998).
Copper compounds like CuOH 2 are utilized as fungicide (especially for downy mildew) in hop cultivation.The amount of Cu in hop cones has been reported to be about 500 mg/kg when the total amount of Cu applied is not higher than 15 kg/ha.Correlation between the dose of *Corresponding author.E-mail: daniel.osorio@food.lth.se.
Author(s) agree that this article remains permanently open access under the terms of the Creative Commons Attribution License 4.0 International License applied cooper and its content in hops has not yet been reported (Weihrauch et al., 2015;Krofta et al., 2012).The aim of this work was to investigate the copper content as well as to assess the influence whether beers containing high amounts of hops shows higher Cu content.For this study 19 different brands of beer commercially available to consumers in Sweden were assessed using flame atomic absorption spectrophotometry (AAS) by direct aspiration of the beer.

Beer samples
Samples used in the present study were purchased in Lund, Sweden on the 11 th August 2014 at the state owned national retail network "Systembolaget".Table 1 shows the beers that were selected which reflect a wide range of beer types available to consumers in Sweden.The samples were stored at 4°C until analysis was performed.
Prior to analysis, beers were degassed in an ultrasonic bath (VWR, Lund Sweden) for 15 min after they were filtered using qualitative filter paper (Munktell, Sweden) in order to remove any large suspended material.

Atomic absorption spectroscopy (AAS)
A Varian SpectrAA 640 atomic absorption spectrophotometer (Varian, Mulgrave, Victoria, Australia) was used at a slit width of 0.5 mm, with a 5 mA Cu hollow cathode lamp operating at 324.7 nm.Beer samples were atomized using an acetylene/air gas mixture.The samples were directly injected in the AAS following the method described by the European Brewing Convention Analytica-EBC (2008) Section 9.14.3.To each beer sample, standard additions of copper were made in the range of 0 to 0.6 ppm.The copper concentration in the beer samples was obtained by extrapolation to zero concentration from the absorbance vs. copper concentration plot.

RESULTS AND DISCUSSION
The results for the Cu content in the 19 beers are given in Table 2.The results show that the Cu content in the beers varied from 0.02 to 0.45 mg/L.The highest Cu concentration was found in sample 6, while the lowest were samples 3 and 19.The maximum value Cu-content in drinking water in the European Union is 2 mg/L (WHO, 1996) and for comparison, all beer samples in this study were well below that limit.In Figure 1, the linearity for the method is shown for Boddingtons beer.
As shown in Table 1, the results in the present study do not suggest that the Cu content is higher as a result of high hop dosage (high bitterness) as in samples 2, 8, 10, 13 and thus, the Cu content seems to be determined by other factors such as water, other ingredients, equipment, etc.

Conclusions
A simple procedure based on flame atomic absorption spectrophotometry (AAS) was performed without sample digestion to determine the Cu content in different beers.Similar range of results was previously reported in literature, showing that the Cu content differs among different brands.Furthermore, the results also revealed that the Cu content in beers is not directly proportional to the amount of hops added in those beers.However, the present study confirmed the fact that the Cu content in beers available to consumers in Sweden are below the permissible levels in drinking water (2 mg/L).

*
The detection limit is 0.01 ppm; **Data are expressed as mean (SD, CV) of nine measurements; ***Error percentage was calculated from the error in the slope and intercept of the regression line.

Table 1 .
Beers used in the Cu analysis.

Table 2 .
Cu concentrations (mg/L) for the investigated beers.