Environmental Engineering Reference
In-Depth Information
composition and global protein potential. Protein containing biomass under
investigation for amino acid recovery includes agricultural residues such as maize
and wheat, dried distiller's grains with solubles (DDGS), sugar beet and sugar
cane vinasse and leaf, wheat straw, rapeseed, soybean, sunflower seed and jatropha
seed meal, as well as micro- and macroalgae and poultry feather meal. Algae is
seen as a particularly promising source of protein for chemical production; the
large quantities of algae likely to be grown will produce significant volumes of
protein-rich waste that is currently viewed as unpalatable and therefore only
of value for animal feed [99]. By combination of the wt% of protein in the biomass
and the amino residue composition of that protein, a representative wt% for each
amino acid could be calculated [98]. The range of wt% (dry) values for each amino
acid over the selection of investigated agricultural residues is included in Table 4.2.
The lower wt% values in the range for each amino acid are typically from
wheat straw or sugar beet leaves as each contains less than 5% protein. Higher
yields are possible from protein-rich sources such as poultry feather meal (>85%
protein content) and microalgae (>60% protein content in
Spirulina
). These other
protein sources also have distinctly different compositions of amino acids, with
some residues present in significantly higher abundances compared to agricultural
wastes. For example proline, serine and glycine are each present in poultry feather
meal in quantities greater than 7 wt%, while their highest content in the agricultural
residues investigated was 3.7, 2.3 and 2.5%, respectively.
Examples exist which demonstrate the production of small building-block
molecules from the thermal treatment (>120°C) of protein. For example, it is known
that acrylamide is formed during thermal decomposition of proteins rich in aspartic
acid, alanine and methionine residues, such as olive water [100-102]. These stud-
ies of the thermal treatment of proteins are focused more on the potential risk of
producing harmful chemicals such as acrylamide in the processing of food than
the generation of platform molecules; nevertheless, they highlight the potential for
this route in the future if yields and selectivity can be increased [103].
4.4.4
Extracts
Many bio-based chemicals utilised today fall within the category of extracts,
which are chemicals present within biomass that can be removed via an extraction
process such as the use of solvents or the pressing of seeds. Most of these
chemicals traditionally extracted from biomass are secondary metabolites such as
triglycerides, terpenes, phenolics and tannins, carotenoids, sterols and flavonoids.
However, the vast majority of secondary metabolites will likely prove too
expensive and present in too little abundance to be classed as significant platform
molecules. Most extracts are isolated from biomass in yields of less than 1 wt%,
typically as impure mixtures, and involve expensive purification processes,
resulting in products of low volume but potentially high value. For most extracts,
their use in the form as isolated from biomass will prevail, with high-value
