Some researcher tried to utilize PKM through various ways. Yopi et al. 2006 used PKM as a substrate to produce functional oligosaccharide such as
mannose and manno-oligosaccharide. Utilization of PKM for produc tion of -
glucosidase and -mannase by Aspergillus niger FTCC 5003 in solid substrate fermentation using an aerated column bioreactor was already tried by
Abdeshahian et al. 2010
a
2010
b
. To produce bioethanol, Cerveró et al. 2010 tried to hydrolyze fermented PKM using Saccharomyces cerevisiae.
2.2 Polysaccharides in PKM
Polysaccharides are carbohydrate containing many hundred or even thousands of monomeric unit called monosaccharides which connected by
covalent bond called glycosidic bonds. Cellulose is a linear condensation polymer consisting of glucose units joined together by -1,4-glycosidic bonds. The
glycosidic linkage acts as a functional group, and this along with the hydroxyl groups mainly determine the chemical properties of cellulose. The PKM contain
12 of cellulose. Cellulose has a low digestibility or even indigestible in poultry Sundu Dingle 2003.
Hemicellulose is structure of polysaccharides of plant cell wall, in close association with cellulose and lignin. Hemicellulose is mixture of polymer made
up of sugars mostly not glucose and sugar derivative. The monomers of hemicelullose consist of three hexoses glucose, galactose, and mannose and two
pentoses xylose and arabinose. Most of the main-chain sugars on hemicellulose structure are linked together by -1,4-glycosidic bonds Moreira Filho 2008. In
PKM the biggest content of hexoses is mannose Cerveróa et al. 2010 Düsterhöft et al. 1992. The complete sugar compositions of PKM are shown in
Table 2. Table 2. Sugar composition of PKM
Component References
Cerveróa et al. 2010 Düsterhöft et al. 1992
Glucose 7.7
1.3 Xylose
2.6 3.9
Arabinose 1.1
1.8 Galactose
1.9 2.6
Mannose 35.2
59.6
sugar reported as anhydrous form; NSP initially comprised 80.39 of each 100g cell wall
material.
According to the main sugar residue in the backbone, hemicellulose has different classification e.g., xylans, mannans, glucans, glucoronoxylans,
arabinoxylans, glucomannans, galactomannans, galactoglucomannans, β-glucans,
and xyloglucans. In total NSPs, PKM contain about 78 of mannans. On a dry matter basis, PKM have been estimated to have 30-
γ5 of -mannans. Mannans in palm kernel resembles very much cellulose by being crystalline, hard and water
insoluble. Mannans are found in the cell wall and impair the digestibility and utilization of nutrients either by direct encapsulation of the nutrients or by
increasing the viscosity of the intestinal contents. This causes a reduction of the hydrolysis rate and the absorption of nutrients in the diet Sundu Dingle 2003.
Lignin is a complex aromatic heteropolymer, composed of phenylpropanoid aryl-C3 units, linked together via a variety of ether and C–C
bonds that most commonly derived from wood, and an integral part of the secondary cell walls of plants.
The major type of linkage is the -aryl ether linkage, containing an ether linkage to another aryl unit at C-2 of the C3 chain; the
biphenyl linkage, containing an aryl C–C bond; the diarylpropane linkage contains a C–C bond at C-2 of the C3 chain to a second aryl ring; the diarylether
linkage contains an ether linkage between two aryl rings; the phenylcoumarane linkage contains a dihydrofuran ring fused to an aryl unit; the pinoresinol linkage
contains a linkage formed by two fused tetrahydrofuran rings Figure 2 Bugg et al
. 2011. Lignin is more hydrophobic than the hemicellulose and cellulose Ahmed et al. 2001. PKM contain 15.1 of lignin Cerveróa et al. 2010.
Figure 2. Major type of linkages found in lignin Bugg et al. 2011
2.3 Polysaccharide Degrading Microorganisms
