Starch, a polymer of glucose units, functions as a sugar store in many plants. It is a mixture of two polysaccharides: amylose and amylopectin. Amylose is the polysaccharide equivalent of the disaccharide maltose and consists of alpha (1-4) linked D-glucopyranose units. This axial configuration of the glycosidic link reduces the strength and abundance of intermolecular hydrogen bonds between amylose molecules when compared with cellulose.
Amylose has an approximate degree of polymerisation (DP - number of monosaccharide units) of 2000 and the polysaccharide forms a helix with six glucose units in each turn. However, amylose is usually a minor component of most starches with amylopectin being the major constituent. Amylopectin again contains glucose units linked through alpha (1-4) bonds; however, there are also alpha (1-6) branches that occur every 24 to 30 glucose units in plants. Amylopectin also has a much higher DP than amylose (e.g. 200,000 residues in potatoes). It cannot coil into a long helix, however, because of the extensive branching, and the fact that the chains that do exist before branching are too short. This means that no compact intermolecular alignment, and hence no significant hydrogen bonding, can take place. This accounts for its extensive solubility, especially when compared with cellulose.
Compared to sucrose, the conversion of starch to ethanol is more complex since the polysaccharide is more resistant to hydrolysis, which means that catalysts are required. However, it is a lot easier to hydrolyse starch than cellulose due to the extensive hydrogen bonding of the latter and the complex lignocellulosic matrix it is contained within.
The main starch-producing feedstocks that are used for biofuel production are wheat (Triticum aestivum) and maize/corn (Zea mays). In a maize to ethanol dry-mill facility the maize is ground to a mash and heated in a cooker where the starch is enzymatically-hydrolysed using amylases and the liberated sugars are then fermented using yeasts. The main products are ethanol, and dried distillers grains which can be used in animal feed.
Maize wet-mills can produce, in addition to ethanol, an array of co-products including oils, proteins, fibre, and nutrients. That is possible because the germ, starch, gluten, and fibre are separated. Furthermore, after hydrolysis, the starch can be enzymatically converted to sweeteners (e.g. a high-fructose content syrup) as an alternative to fermentation to ethanol or other products.
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Analysis Packages for StarchThe Celignis Analysis Package(s) that determine this constituent are listed below:
| Starch |
Equipment Used for Starch Analysis
|Ion Chromatography A Dionex ICS-3000 system that is equipmed with electrochemical, conductivity, and ultraviolet-visible detectors.|
Additional MaterialClick here to learn more about our various methods for analysing oligosaccharides.
We can determine the Starch content of biomass, click here to learn more about our various biomass analysis methods.