Lipid composition of Hevea brasiliensis latex and dry rubber: Characterization and relation with some physical properties

The purpose of this work was to characterize the lipid composition of natural rubber latex and unsmoked sheets from Hevea brasiliensis clones, namely RRIM600, GT1, PB235 and BPM24 and to study correlations between this composition and some properties of raw rubber such as Initial plasticity, Plasticity Retention Index and Breakdown Index. 15 samplings have been performed over a 3 years period. Lipid contents were found to be clonal dependent. They were in the range of 2.5% to 3.7% vs dry rubber for fresh latex and 2% to 3.3% for sheet rubber. Lipids were separated by families i.e. phospholipid, glycolipid and neutral lipid and each family was characterized. In sheet rubber the proportion of each family was found to be 80%, 15%, and 5% respectively. Polar lipids were much less present in sheet rubber than in latex, which suggested an effect of the sheet production process on lipid composition. The major fatty acid detected in lipid extracts was linoleic fatty acid except for PB235 clone which contains a rare fatty acid in important quantity, namely furanoid fatty acid. The unsaponifiable fraction of lipid extract, analyzed by GC-MS, was constituted by fatty alcohols (9%), [gamma]-tocotrienol (12%), [alpha]-tocotrienol (5%), stigmasterol (7%), [bêta]-sitosterol (50%), and [delta]5-avenasterol (17%). The unsaponifiable composition of rubber sheet was not different from that of latex. Concerning glycolipids, which have been identified by HPLC-MS, four main glycolipids, namely monogalactosyl diglycerides (MGDG), digalactosyl diglycerides (DGDG), esterified steryl glucosides (ESG) and sterylglucosides (SG) were detected in the respective relative proportions of 7%, 47%, 13%, and 33%. Phospholipids consisted of phosphatidylinositol (PI), phosphatidyl ethanolamine (PE), phosphatidic acid (PA), lysophosphatidylinositol (LPI), phbsphatidylcholine (PC), and lysophosphatidylcholine (LPC) in the respective proportions of 3%, 4%, 9%, 2%, 57% and 25%. The analyses of physical properties of rubber such as Initial plasticity, PRI, Mooney viscosity and breakdown index permitted to distinguish clear differences between clones. A few correlations between some lipids characteristics and physical properties of rubber are discussed. (Résumé d'auteur)