Identification of non-isoprene compounds involved in the storage hardening of natural rubber by latex reconstitution.

Latex from two Hevea brasiliensis clones (RRIM600 and PB235) was fractionated by centrifugation to isolate (i) C-serum, (ii) the bottom fraction (lutoids), and (iii) the rubber particle fraction. These fractions were subsequently recombined in different proportions to produce reconstituted latexes, which were used to prepare air-dried rubber sheets (ADS). The storage hardening behavior of these ADS was then investigated. The increase in Wallace plasticity (ΔP) was measured following an accelerated storage hardening test (ASHT). In addition, the detailed biochemical composition of ADS including lipids (neutral lipids, glycolipids, phospholipids, and free fatty acids), proteins, and minerals (S, P, K, Ca, and Mg) as well as their mesostructural characteristics, were analyzed. The clonal origin of the latex strongly influenced both biochemical composition and the storage-hardening behavior of ADS; however, common trends were observed across both clones. Notably, the C-serum fraction emerged as the primary driver of storage hardening. To further elucidate the relative contributions of non-isoprene compounds to this process, a multivariate regression analysis was performed. Total protein content showed a strong correlation with storage hardening in both clones. The role of minerals could not be clearly established due to strong collinearity with other biochemical components. In contrast, neutral lipids, glycolipids, phospholipids, and free fatty acids exhibited no significant positive correlation with ΔP. Overall, this study combining an original experimental design with robust statistical analysis provides new insights into the role of non-rubber components in the storage hardening of natural rubber.