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Copper in Wines: Neglected Effects?

G.J.Troup(a), D.R.Hutton(a), S.J. Longford(b), I.Cheah(b), and Kathy Macfarlane(b).

(a) School of physics and Materials Engineering, and (b) School of Chemistry, Monash University, Clayton 3800, Victoria, Australia.

Abstract

Copper (Cu) occurs certainly in some, maybe in all wines, because of its presence in the soil. Evidence from Electron Paramagnetic Resonance (EPR) is given showing that Cu may ‘hide’ in wines as Cu+, clearly an antioxidant. Cu is also necessary for the physiology of the human body.

Introduction

Copper occurs in many, if not all soils. Modern extensive use of Cu in the wine industry commenced in Europe in the 1880s for fungus control [1]: this practice would have spread to other winemaking countries, so vineyard soils low in Cu would have had their concentrations increased.

EPR is a useful and sensitive tool for observing Cu++: Cu+ is unobservable, not being paramagnetic. Cu++ is usually observable at room temperature, or at least at the temperatures simply obtained by using liquid N2. In the experimental work to be described, measurements were made at room temperature for solids, and at temperatures below 0 C for frozen solutions: for the latter case, cooled dry N2 was used. A Varian E-line X-band (~ 9.1 GHz. ) EPR spectrometer was the measuring apparatus.

Experimental Results

During the measurement of the free radical concentration in the red wine fractions anthocyanins, flavonoids and non- flavonoids [2], a Cu++ signal was observed in the flavonoid fraction, but not in the others; nor was it observed in the complete wine from which the fractions were obtained. The Cu++ presence was put down to the changeof pH required to

obtain the flavonoid fraction separation. During neither the fractionation nor the EPR experiment was contamination by Cu possible.

Some South Australian red wines throw a red waxy bottle deposit shown to be an anthocyanin protein compound [3]. Samples of the deposit, when examined by EPR, showed a strong Cu++ signal with N superhyperfine structure (from the protein) as well as the free radical signal expected to be associated with the anthocyanins [4]. Again no contamination by Cu was possible.

Cu is commonly used in recipes for ‘model wines’ [5,6]. In a series of experiments to observe the effect of Vitamin C on the ageing of a model wine, the samples were artificially aged by being kept at 40 C. for three months. From the now brown mother liquor, a fluffy brownish precipitate was formed. When examined as a solid, it gave a Cu++ spectrum and free radical signal as might be expected.

This result encouraged us to examine a similar precipitate formed from a natural Chardonnay wine produced by the Australian Wine Research Institute and artificially aged as above. The full wine gave no Cu++ signal but the precipitate did, as well as a free radical signal: the Cu++ signal had neither hyperfine nor superhyperfine structure [7]. No Cu contamination was possible.

While measuring the change of phenolic concentration in free dried red grapeseed with maturation, by using EPR [8] we found a Cu++ signal in the phenolic extract made with 2:1 acetone water for 24h. This signal was observed at 77 K and contained N superhyperfine structure, but had disappeared at room temperature, presumably because of the lines being broadened as the temperature rose. Again no Cu contamination was possible.

Discussion.

These experimental results, initially quite unexpected (especially for the red wine waxy bottle deposit), indicate the presence of Cu in the wines studied, most probably in the form of Cu+. As Cu+ is oxidisable , it is clearly an antioxidant and should be taken into account in considering the antioxidant action of red wine in particular. It is interesting that Cu is often found closely associated with phenolics: in the commercially available red clover extracts Promensil and Trinovin, which contain polyphenols that mimic oestrogens, Cu++ signals with N superhyperfine structure were found [9].

But there is more.........

“Copper has been recognised as an essential trace metal for living organisms since the late 1930s. Its role as a cofactor for crucial enzymes has been well established. These include cytochrome c oxidase (the terminal enzyme in electron transport and respiration), Cu/Zn superoxide dismutase (SOD 1) and ceruloplasmin (which deal with superoxide and other potentially damaging radicals)......The chemistry of copper makes it an ideal participant in redox reactions, as it easily cycles between the cuprous and cupric states.” [10].

It should be pointed out that there is a special ‘chaperone protein’, simply called the chaperone protein for SOD1, (CCS), which keeps SOD1 supplied with Cu! SOD is a great disabler of the superoxide radical, O2-., which is extremely active because of its charge as well as the free radical.

Cu is also part of the normal prion protein, which is an extracellular membrane component of neuronal cells. Abnormal prion lacking Cu is thought to be involved in some psychiatric disorders in humans, and in ‘mad cow disease’.

So, while enjoying the benefits of the phenolics in wines, we should perhaps occasionally remember that their companion copper is chaperoning us against the possible bad effects of the superoxide radical!

References

[1] W.Younger, (1966) Gods Men and Wine, p425: The Wine and Food Society Ltd. London, UK. .

[2] G.J.Troup, D.R.Hutton, D.G. Hewitt, C.R.Hunter (1994), Free Radicals Res. 20, 63.

[3] Z.Peng, E.J.Waters, K.F.Pocock,P.L.Williams (1996) Aust. J. Grape and Wine Res. 2, 25.

[4] G.J.Troup, C.R.Hunter (2002) Annals New York Acad.Sci. 957, 345.

[5] G.J.Troup et al. (1994), ANZ Wine Industry Journ. 9, 145.

[6] M.Mitri (2003) Ph.D.Thesis (unpublished), School of Chemistry, Melbourne University.

[7] J.A.Kennedy, G.J.Troup et al. (2000), Aust. J.Grape and Wine Res. 6, 244.

[8] M.Mitri, G.Scollary, G.J. Troup, D.R.Hutton, J.R.Pilbrow (2003), ANZ Inst.Physics Condensed Matter Conf., Wagga Wagga (February), final paper.

[9] G.J.Troup et al. (2000) ANZ Soc. Mag. Res.Conf. Mount Buller (February), poster P52.

[10] M.C.Linder, (2001) Copper and genomic stability in mammals, Mutation Research 475, 141 -152.

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