The parameters we have investigated are the type of organic solvent (cyclohexane, THF and a mixture of cyclohexane:ethanol (39:1, v/v)) and the temperature (35 and 50°C). At the end of the solubilization, the samples were centrifuged and separated into 2 phases named: macrogel (pellet, unsoluble fraction) and microgel (supernatant, soluble fraction).
For each extraction conditions (4 treatments), the nitrogen contents of both macrogel and microgel were measured. USS homogenization prior to nitrogen content measurements it not necessary as non-homogenized and homogenized USS exhibit similar nitrogen contents. Cyclohexane is more appropriate than THF to increase the protein extraction yield in pellet. Increasing the temperature from 35°C to 50°C during the solubilization step does not improve the protein extraction yield in pellet. Although the values of nitrogen contents in pellet are very close for both treatments T0 and T2, it seems that the presence of ethanol in cyclohexane (T0) slightly improves the extraction yield as compared to 100% cyclohexane. For all Hevea clones studied, treatment T0 appears to be the most appropriate treatment to extract proteins from USS.