P. PELLERIN* , M.A. O'NEILL**, Cécile PIERRE*, Marie-Thérèse CABANIS***, A.G. DARVILL**, P. ALBERSHEIM** et M. MOUTOUNET*
*Institut National de la Recherche Agronomique, Institut des Produits de la Vigne,
Unité de Recherches des Polymères et des Techniques Physico-Chimiques,
2 place Viala, 34060 Montpellier Cedex (France)
**Complex Carbohydrate Research Center, The University of Georgia, 220 Riverbend Road, Athens, GA 30602-4712 (USA)
***Centre de Formation et de Recherche en oenologie, Faculté de Pharmacie,
Université de Montpellier I, avenue Charles Flahault, 34060 Montpellier cedex (France)
Abstract : Wine is believed to be a significant source of lead in the human diet even though the lead content of wines has decreased considerably over the last thirty years. Nevertheless, the lead content of wines must be reduced to a minimum since this heavy metal is highly toxic. The plant cell wall pectic polysaccaride rhamnogalacturonan II (RG-II) is a predominant anionic molecule in red wine. R-G II exists as a dimer (dRG-II-B) that is cross-linked by a 1 : 2 borate-diol ester and forms complexes in vitro with lead and other selected di- and tri-valent cations. One mole of dimer binds at least 1 mole of Pb2+. We have now determined the amount of lead in wines that is bound to dGR-II-B since previous studies have suggested that most of the lead in wine is bound to an anionic macromolecule. Seven wines, with lead concentrations between 30 and 110 µg/l, were obtained from different grape varieties harvested at different vintages and vinified by differents procedures. Two chromatography steps, adsorption on a polystyrene-divinylbenzene resin and size-exclusion on a Superdex® 75-HR column, have been used to purify a d-RG-II-B-lead complex which contained at least 85 p. cent of the total lead of each wine. The dRG-II-B-Pb complex is stable at the pH of wine and is present in a wine that was produced in 1988. The dRG-II-B present in red (- 100mg/l) and white (-200mg/l) wines can bind at least ten-fold more Pb2+ than is typically present in wine. Our study is the first to show that in wine most of the lead is complexed with a pectic polysaccaride that is not degraded during vinification. DRG-II-B is also known to form complexes with other cations, including strotium and barium. However, it is not known what role dRG-II-B has in determining the metabolic fate in humans of toxic cations present in wine.
Key words : wine, lead, Pb2+, cation, rhamnogalacturonan II, pectic polysaccaride, nutrition, health, toxicity