Dextrose refining

To achieve a pH of 6 or lower for the effluent from a char filter, it is necessary to acid temper the rebumed bone char after it has been returned to the filter, i.e., to treat the char with dilute acid. It is evident, therefore, that bone char is not well adapted, in this respect, to dextrose refining. Consequently, one obvious direction in which an improvement in the conventional process could be made would be the devising of an adsorbent which would buffer on the acid side of neutrality instead of on the alkaline side. 

Alternative solutions to the problem of pH control in dextrose refining are the use of powdered activated carbon, which decolorizes the liquor but removes little ash or the use of ion exchangers, which effect a substantially quantitative removal of ash, plus treatment with powdered activated carbon to remove color. 

Manufacture. HFS containing 42% fmctose is produced commercially by column isomerization of clarified and refined dextrose hydrolyzate using an immobilized glucose isomerase. Enriched symp containing 90% fmctose is prepared by chromatographic separation and blended with 42% HES... 

In 2002, approximately 2.2 billion bushels of corn were processed in the United States for the production of food, fuel, and industrial products. Of that 2.2 billion bushels, 19.22 million tonnes (757 million bushels) were used for high fructose corn syrup (HFCS), glucose and dextrose, 6.34 million tonnes (250 million bushels) for pearl starch, 26.69 million tonnes (1051 million bushels) for fuel and beverage alcohol, and 4.75 million tonnes (187 million bushels) for cereals and other products (Corn Refiners Association, 2003). More than 50% of the com processed in the United States is done so using the corn wet milling process. 

The problem of crystallizing dextrose from starch conversion liquor in a form which would allow separation from the viscous mother liquor was attacked in the latter part of the nineteenth century by various workers. The most successful efforts were made by Behr in 1881.3 Corn starch was hydrolyzed at low concentration, the refined product was concentrated, seeded with a very small proportion of pure anhydrous dextrose crystals, and it was then allowed to stand without agitation in heated rooms. Care was taken to exclude any traces of dextrose hydrate crystals. After several days the crystalline magma was separated and washed in centrifugal filters. By this means individual crystals of anhydrous dextrose of suitable size were obtained and the product... 

During the first World War, the Corn Products Refining Company attempted to improve the methods of manufacturing dextrose to obtain a pure product at low cost. A process was developed in 1918 by Porst which produced chemically pure dextrose but cost of production was still high. 

Fig. 4.—Alpha dextrose monohydrate from refined starch conversion liquor. Magnification, 50.

IV. Application of Ion Exchange Refining to the Commercial Manufacture of Crystalline Dextrose... 

The application of ion exchange refining to the dextrose manufacturing process affords a number of advantages, some of which are briefly discussed below.22... 

Crystallization yield is increased by removal of colloidal inhibitors and also by removal of ash, which, when present, causes an increase in dextrose solubility. Growth of more uniform crystals, which permits better separation from the mother liquor, takes place. Figure 7 shows the type of crystals usually obtained from liquors refined by ion exchange treatment. 

Application of ion exchange refining to the process for the manufacture of dextrose may be understood from the following description of such a process. Triple-washed starch is diluted with ion-free water to the desired concentration and is acidified with a definite quantity of mineral acid such as hydrochloric or sulfuric. It is desirable that the acidified starch slurry be held for at least thirty minutes in order to permit an effective equilibrium acidity to be reached. The starch slurry may contain a quantity of soft water salts which consume acid, and since this consumption is variable, the acidity is checked and adjusted to the desired level following the holding period. The conversion is then carried out at elevated temperature and under pressure for a period sufficient to yield maximum dextrose. The conversion may be carried out batchwise in an autoclave, or continuously. 

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). 

Mother liquor at 90% dextrose from the first crop of crystals can be concentrated and crystallized in a similar manner to recover an additional crystal crop. Depending on quality, some mother liquor can be partially recycled to the initial crystallization step to increase crystal-phase yield as a single crystal crop. The overall yield depends on the dextrose content of the original hydrolyzate and the extent to which hydrolyzates are refined. The mother liquor from the second crystallization contains less than 80% dextrose. The material is evaporated to 71% solids and sold as hydrol to the tanning and fermentation (qv) industries and for the manufacture of caramel color. 

Invert sugar. Invert sugar, sometimes referred to as partially inverted refiner s syrup, is produced by acid or enzymic hydrolysis of the disaccharide sucrose into its 2004 component pails of fructose and dextrose (glucose). Invert syrups usually contain a mixture of sucrose, fructose and dextrose. The main advantage of such a syrup is the reduced likelihood of crystallisation and an increase in osmolality, which may be useful in reducing spoilage risk. 

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