The interaction of the pectic polysaccharide Rhamnogalacturonan II with heavy metals and lanthanides in wines and fruit juices

Abstract

T he speciation of metals with biological compounds (proteins, peptides, amino acids, etc.) is the subject of i n c reasing interest since the complex ation of heav y metals may reduce their toxicity and their bioava l a i b i l i t y. However, there are a limited number of studies concerning the speciation of metals with plant polysaccharides. This is somewhat surprising since plant cell walls contain polysac-charides (pectins) that contain a high proportion of negatively charged glycosyl-residues. In this article, we discuss the cation-binding characteristics of pectins and in particular describe the selective binding of heavy metals and lan-thanides by the structurally complex pectic polysaccharide rhamnogalacturonan II (RG-II). The complexation of divalent cations with the carboxylic acid groups of uronic acids from pec-tins is well establ i s h e d. H ow ev e r, one pectic p o ly s a c ch a r i d e, R h a m n o g a l a c t u ronan II, ex i s t s as a borate ester cross-linked dimer that forms coordination complexes with selected di-(Pb 2+ , Ba 2+ and Sr 2+) and trivalent (lanthanides) cations. The cation-rhamnogalacturonan II complex accounts for the majority of lead in wines and fruit juices and may also account for some of the heavy metals present in plant cell walls. M 32