Starch processing

The finished starch slurry from the final hydroclone stage may be further processed in alternative ways (a) dried directly and sold as unmodified com starch (b) modified by chemical or physical treatment in a way that preserves the granule structure, then rewashed to remove residual reactants, and dried (c) gelatinized and dried (d) chemically or physically modified and then dried (e) hydrolyzed either completely to D-glucose or partially hydrolyzed to give mixtures of soluble oligosaccharides and D-glucose (see Chapter 21), which can be fermented to yield ethanol and other products. 

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Worldwide consumption of industrial enzymes amounted to approximately 720 million in 1990 about one-third was accounted for by the U.S. market. Estimation of worldwide consumption is difficult because official production figures are scarce. A relatively large portion of the production of starch-processing enzymes is for internal consumption. Furthermore, the currency used for the estimation also influences the result considerably. 

Nigan P and Singh D. 1995. Enzyme and microbial systems involved in starch processing. Enzyme Microb Technol 17 770-778. 

Starch processing is a fairly mature technology, but recent advances in starch processing have improved the economics and efficiency of the process. For example, a simpler low-pH a-amylases process has been developed, improving the ethanol yield and reducing costs [20], The other major advance is the development of enzymes that function on raw, uncooked starch, thereby improving overall process economics [21, 22],... 

The category Enzymes as industrial catalysts , including the starch-processing, antibiotics and the fine-chemicals industry, is covered in chapter 4. 

The com starch processing industry provides a veiy good example of how biocatalysts can be successfully employed in bioprocessing on a very large commercial scale. Just... 

One of the factors that has allowed the rapid post-WW2 expansion of the com starch processing indnstry has been rising agricultural productivity resulting in a steady increase in per capita cereal prodnction, despite the rising world population (Figure 4.5). By the year 2000, starch production estimates are for about 900x10 ton/a, about 75% from com, and with a (1990) value of 80 /ton Also over the... 

Starch Liquefaction. Starch in its natural state is only degraded slowly by CC-amylases. To make the starch susceptible to enzymatic breakdown, it is necessary to gelatinize and liquefy a slurry with a 30—40% dry matter content. Gelatinization temperature depends on the type of starch (67) com is the most common source of industrial starches followed by wheat, tapioca, and potatoes. Liquefaction is achieved by adding a heat-stable a-amylase to the starch slurry. The equipment used for liquefaction may be stirred tank reactors, continuous stirred tank reactors (CSTR), or a jet cooker. Most starch processing plants liquefy the starch with a single enzyme dose in a process using a jet cooker (Fig. 9). 

Alkali was the first chemical used in corn wet-milling,275 but was quickly abandoned in favor of sulfur dioxide. Researchers over the years have tried to refine the use of alkali for starch processing,1718 276 because of the ease with which alkali solubilizes endosperm protein. An alkali wet-milling process which yields —2% more starch and has —40% lower capital cost has been developed.277... 

A possible potato starch process which attempts to combine the best elements of the described processes (Figure 11.8) and to find an optimum which can be implemented is shown in Figure 11.9. This process is described in more detail in the rest of the chapter. 

Figure 11.9 A schematic overview of a potato starch process.

Figure 11.14 Reduced efficiency curves [G (X)] fora potato starch process.

An optional sieving block is displayed in the schematic diagram of the starch process (Figure 11.9). Depending on the origin of the potatoes, the starch slurry can be contaminated (with wood, sand, peat, etc.) with particles with sizes of 90 pm and larger, and with densities the same as or higher than that of starch. There has been no separation step for this kind of material (for the fraction with diameters <125 pm)... 

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