BIOMASS COMPOSITION, PROPERTIES, AND CHARACTERIZATION - Biomass as a Sustainable Energy Source for the Future - page 48

(Koh and Ghazi, 2011). Moreover, the plant is useful for improving agricultural soils
(root system) and acts as a drought-resistant, shade-rich hedge, thus protecting crops
that are grown inside by preventing roaming cattle from entering. The hedge also pre-
vents erosion and the species has the unique property of acting as natural “ pesticide ”

protector.

2.3.2 Proteins

The main biomass structures, apart from chitin, in which nitrogen is incorporated, are
proteins. These are biopolymers consisting of -amino acids (20 primary species exist

in nature) joined by peptide linkages. Table 2.5 shows the protein content of several
relevant biomass types and biogenic residues. The table shows a broad spectrum of
protein contents and related to this is the material

α

s nitrogen content. When used
as source for energy supply in thermochemical conversion processes, eventually,
the high fuel-bound nitrogen content may lead to increased NO x and/or N 2 O emis-
sions. In novel biorefinery concepts, the proteins may be retrieved from biomass
sources and processed into higher-added-value products (food and feed supplements)
before usage of the remaining residue for energy supply. More about this is discussed
in Chapter 15.

'

2.3.3 Starch and Free Sugars

Apart from cellulose, another biopolymer that is composed of C 6 sugar (glucose) units
is starch; the difference with cellulose is that its segments constitute -glycosidic lin-

kages, so that starch is a stereoisomer of cellulose. As a consequence of this structural

α

TABLE 2.5 Typical protein content of some biomass types

Biomass Protein content (wt%) References

Softwood 0.2-0.8 Leppälahti and Koljonen (1995)

4 a Wheat straw Silva et al. (2011)

Corn stover 5 Dale and Kim (2006)

Olive oil cake 6 Ramachandran et al. (2007)

Needles and leaves 7-8 Leppälahti and Koljonen (1995)

Corn 10 Dale and Kim (2006)

Palm kernel cake 19 Ramachandran et al. (2007)

Alfalfa 20 Dale and Kim (2006)

Dried distiller's grains
and solubles (DDGS)

25 Kim et al. (2008)

Rapeseed cake 36 Koutinas et al. (2007)

Cottonseed cake 40 Ramachandran et al. (2007)

Soybean 40 Dale and Kim (2006)

Chicken manure 47 El Boushy et al. (1985)

Soybean cake 48 Ramachandran et al. (2007)

a Depending on size fraction after cutting and sieving.