Starch saccharification processes

Conversion. Conversion describes the enzymatic starch hydrolysis processes, Hquification, and saccharification. 

The purification of saccharified starch depends on the raw material used, and may be different from plant to plant. When the starch slurry is hquefied ia a jet cooker the saccharification process is carried out at 55—65°C, pH 4—4.5, for 24—72 hours. The subsequent steps consist of filtration or centrifiigation, ion exchange, isomerization, treatment with activated carbon, and evaporation to form a storage-stable product. 

Shiraishi et al. [49,50] immobilized glucoamylase of Rhizopus delemar in monolith structures and used them for saccharification of soluble starch. The process was studied at first in a batch reactor at SOX and 4.5 bar. The simplified kinetic model was developed. A continuous process was realized in a monolith reactor consisting of 10 pieces stacked on top of each other, where the blocks were rotated by ir/4 on their axes. The reaction rate at a glucose concentration of 460 g dm" was approximately two times higher than in a conventional industrial process. Conversion of 47% was reached at a space time of 12 hr. The half-life of enzyme was 79 days. 

The enzymatic production of sugars from starch is one of the oldest processes practiced by mankind. The saccharification of starchy materials by malt in occidental countries and by fungal koji in the Orient for beverage fermentations was conducted as early as there are written records. These saccharification processes were a basis for the earliest recognition during the nineteenth century of the biological catalysts we now know as enzymes. 

In recent years, the liquefaction process by adding enzyme has been widely applied to amylohydrolysis and achieved good results with the development of the enzyme industry. The saccharification process that uses double enzymatic fermentation is an important preprocessing step in the production of starch ethanol. 

Starch saccharification is achieved by either acidic or enzymatic hydrolysis. Controlled processing conditions yield products of widely... 

Extremely thermostable amylases and pullulanases, active above 100 °C and stable/active at acidic pH values wiU significantly improve the industrial starch bioconversion processes of liquefaction, saccharification, and isomerization. The lack of enzymes with these characteristics means that the bioconversion of starch to glucose and fructose must be carried out in a multistage process (step 1 pH 6.0 to 6.5, 95 to 105 °C step 2 pH 4.5, 60 to 62 °C step 3 pH 7.0 to 8.5, 55 to 60 °C),... 

A cost efficient way to utilize wheat in ethanol production has been developed by researchers from Greece and the U.K. This process splits the grain into separate components, separating out the nonfermentable solids, and then uses a group of enzymes to ferment the proteins and starches using a single liquefaction and saccharification step. 

The thermostable CGTase produced by Jhermoanaerobacter sp. ATCC 53,627 is able to liquefy starch at pH 4.5 under standard industrial conditions. It is, therefore, unnecessary to pH adjust the dextrin solution prior to saccharification as is normally done in the industry today. Since there is no need for pH adjustment, significant process advantages are realiz. There is a substantial cost improvement with regard to chemicals, ion-exchange media, charcoal, etc. Also, unwanted by-product formation e.g., maltulose, colored products, base-catalyzed products are reduced. Consequently, these advantages will translate into real savings to the starch industry. 

Starch derived from maize, potatoes, barley, cassava or other somces must be pretreated with hydrolytic enzymes (amylases, amyloglucosidase, proteases), which carry out liquefaction, saccharification and protein hydrolysis, respectively, before it can be fermented by yeasts and other microorganisms into potable or non-potable alcohol. Enzymes can be added in the form of malt (germinated barley) or koji (germinated rice), but this is expensive. Therefore, industrial enzymes have nearly totally replaced malt and koji as enzyme sources, thereby not only improving the economics but also the predictability of the process. 

Refining. After saccharification, the hydrolyzate is clarified by precoat filtration, or possibly membrane filtration, to remove traces of insoluble fat, protein, and starch. Treatment with powdered carbon, granular carbon, and/or ion-exchange resins is then used to remove residual trace impurities, color, and inorganic constituents. The refined hydrolyzate can be dried to a solid product, evaporated to a high dextrose syrup, or processed to crystalline monohydrate or anhydrous dextrose. A typical process for production of crystalline dextrose is shown in Figure 2(7). 

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