Uses of Waste Starch - The Economic Utilisation of Food Co-Products - page 74

5.3.7 Waste Starch as a Source of Chemicals
The chemical industry has relied on fossil resources for decades as a source of
raw materials. However, the concept of sustainable development has recently
attracted a great deal of interest in the utilisation of biomass as a novel source
of chemicals. The concept biorefinery is based on the idea of replacing carbon
molecules from petroleum-based chemicals by plant-extracted carbon
molecules. 78 Waste starch presents a great potential as a source of bioderived
chemicals.
Initially, starch is converted into simple sugars via a depolymerisation
process, which typically involves the use of enzymes. Both a-1,4 and
a-1,6-debranching hydrolases, such as endo-amylases, exo-amylases,
debranching enzymes and transferases, are required in ecient starch
hydrolysis. 79 Once starch is broken down, the glucose monomers can be utilised
as substrates for chemical reactions leading to various chemical products.
Fermentation using micro-organisms leads to different molecules, such as lactic
acid, PHB and succinic acid. Direct conversion of starch to lactic acid was
reported using Lactobacillus amylovorus and Lactobacillus plantarum A6. 80,81
Jin et al. successfully produced L( þ )-lactic acid in a simultaneous sacchar-
ification and fermentation process from starch waste euents using Rhizopus
arrhizus, strain DAR 36017. 82 Furthermore, the same yeast was used by Zhang
et al. to produce lactic acid from waste potato starch. 83 Lactic acid is used in
various industries including food, pharmaceutical and chemical production.
This molecule can also be polymerised to yield polylactic acid (PLA), which has
great potential as bioderived plastic. 84 Waste potato starch can be used as a
viable alternative carbon source for PHB production, using Ralstonia eutropha
NCIMB 11599. Moreover, the production performance with the waste starch
was found to be practically identical to that with glucose. 85
Another very important glucose derivative is succinic acid, which presents
one of the top 12 most useful bioderived building blocks in chemical synthesis
according to the US Department of Energy (Table 5.1). 86 Succinic acid shares
the basic chemistry of petrochemically derived maleic acid/anhydride. It is
also considered as a versatile intermediate for the production of some of the
most widely used fossil-derived chemicals (Figure 5.5). Production of succinic
acid from waste starch derived from the wheat milling process using Actino-
bacillus succinogenes was reported by Dorado et al. This represents a great
prospective for the use of waste starch as an alternative source for chemical
production. 87

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5.3.8 Starch Plastics
5.3.8.1 Starch in Composites
The use of starch in composites is relatively recent compared to its uses in other
applications such as adhesives, paper industry and textiles. Waste starch
presents an attractive feedstock for composite materials due to its low cost,
availability and biodegradability.