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2.1.1.1.2 Proteins

Natural rubber latex collected from the Hevea trees mostly contains about 1-1.5% of total
proteins. However, these proteins can be separated in three parts that consist of 20-27% of the
total proteins absorbed in rubber surface, 47-66% of the total proteins in aqueous serum, and 14-
25% of the total proteins in lutoids (Archer, 1960).

2.1.1.1.3 Lipids and phospholipids

The stability and colloidal behavior of latex depending upon lipids and phospholipids
associated with rubber and non-rubber particles in latex. Lipids and phospholipids associated in
natural rubber latex can be separated in two parts, the first part is phospholipids of the rubber
particles are -lecithin and other lipids are a subgroup of lipids called triglycerides and waxes
and the second part was presented in serum (Sansatsadeekul et al., 2011).

Some physical and chemical characteristics of skim latex serum are given in Table 2.1.
The result shows that there are several limitations of using skim latex serum as substrate for
generate biogas such as low C/N ratio around 7 as well as relatively high inhibitants content.
These inhibitants that contains in the skim latex serum could potentially inhibit the microbial
growth, resulting decrease in biodegradability. Thus, to enhance the biogas production potential
as well as to prevent the risky of the process failure, the usages of anaerobic co-digestion and a
two-stage process is a simply practical approach as previously mentioned. The process involved
in concentration of natural rubber latex by using centrifugation method as shown in Fig. 2.1.