The catalytic capacity of several excreted pectinolytic enzymes obtained from various yeast strains was examined using in vivo and biochemical techniques. Of the 33 yeast strains studied, 30 were isolated from champagne wine during alcoholic fermentation. Only one yeast strain was found to excrete pectinolytic enzymes and was identified as Saccharomyces cerevisiae and designated SCPP. Pulsed-field gel electrophoresis and the polymerase chain reaction technique were used to characterize further this specific strain. Three types of pectinolytic enzymes were found to be excreted by SCPP: polygalacturonase, pectin-lyase and pectin-esterase. These enzymes allow pectin hydrolysis during cell growth.

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Oxidants formed through the interaction between MnO2 and oxalate accumulated in rotten wood have been evaluated as abiotic agents possibly involved in wheat straw ligninolysis. The hemicellulose and cellulose content of straw remained unchanged, and no release of free soluble materials from lignin or polysaccharides could be evidenced. Structural analysis of oxidized lignin in situ has revealed up to 30% and 10% decrease of β-O-4 linked Guaiacyl and Syringyl units, respectively. Lignin phenolic moieties only were directly oxidized by MnO2/oxalate as no structural alteration was observed within extensively permethylated wheat straw. Modifications were also evidenced at the level of the cell wall linked cinnamic acids present in wheat straw. Esterified phenolic acids were more readily oxidized by Mn complexes than ethers analogues, and disappearance of ferulic moieties was always more pronounced than that of p-coumaric acids. The abiotic Mn oxidants generated from MnO2 and oxalate may therefore significantly contribute to the decay and humification process of lignocellulosic material in Nature. Keywords: Manganese dioxide; oxalate; abiotic oxidation; wheat straw; lignin; cinnamic acid; hemicellulose; cellulose

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