Résumé
The latex collected from the Hevea brasiliensis tree is today the only commercial source of natural rubber (NR), the cis-1,4-polyisoprene polymer, a strategic raw material. The Hevea latex is a very complex material both in its structure and composition. In terms of structure, it is a colloidal dispersion where various micrometric objects, mainly rubber particles and lutoids, are dispersed in the cytoplasmic serum (C-serum). The rubber fraction is the most abundant, followed by the C-serum and the lutoids. In terms of composition, the fresh latex contains about 60% of water, 35% of cis-1,4-polyisoprene and 5% of non-isoprene molecules. These non-isoprenes are biochemical compounds mostly including proteins, lipids, carbohydrates and minerals, and their distribution in the fractions of latex is not homogeneous. Although the non-isoprenes represent a minor part of the latex, some of them are retained in NR after latex processing and recognized to play a crucial role on the NR properties. Actually, the non-isoprene molecules are likely behind the better mechanical properties of NR over its synthetic counterpart, but they are also responsible for the high variability of NR quality. This variability of NR quality is a major drawback in NR industry and is directly linked to the latex composition, which is influenced by various physical and physiological parameters. The biochemical composition of latex matters, and this chapter is thus an overview of the protein, lipid, carbohydrate and mineral contents in latex, as well as their distribution in the three main fractions of latex.