Sugar – starch – and carbohydrates – Processes – Carbohydrate manufacture and refining
Reexamination Certificate
2001-01-29
2003-09-02
Brunsman, David (Department: 1755)
Sugar, starch, and carbohydrates
Processes
Carbohydrate manufacture and refining
C127S071000
Reexamination Certificate
active
06613152
ABSTRACT:
The invention relates to a process for preparing a starch dextrin.
Carbohydrate intermediates between starch and the sugars produced from starch by hydrolysis by dilute acids, amylase or dry heat are usually referred to as dextrins. In fact, a dextrin is an oligomer of the glucose monomers, of which starch is a polymer. It is an amorphous, yellow or white powder, which is (partly) soluble in water.
Dextrins are used for numerous industrial applications. Some examples of relevant areas are the adhesive industry, the paper industry, the pharmaceutical industry, the mining industry, the food industry, and the textile industry.
Sometimes a distinction is made between malto-dextrins and pyrodextrins. The first being the product of dextrinization of starch using an enzyme; the latter being the product of dextrinization of starch using heat. The large scale production of dextrins for non-food applications primarily concerns pyrodextrins.
On the market, dextrins are available in three major varieties: British gums, white dextrins and yellow dextrins. The chemical changes occurring in starch during dextrinization are complex and not fully understood. It appears that three major reactions may be involved. The relative role of each will vary depending on whether white dextrins, yellow dextrins or British gums are being produced. The major reactions include hydrolysis, transglucosidation and repolymerization. These reactions have been described in “Modified Starches: Properties and Uses”, O. B. Wurzburg, CRC Press Inc., 1987.
The hydrolysis is believed to involve an acid-catalyzed scission of &agr;-D-(1,4), and probably &agr;-D-(1,6) glucosidic linkages in the starch. As a result, there is a decrease in the molecular weight of the starch which is reflected in a decrease in viscosity of a solution of the dextrin that is being prepared. Further, the number of aldehydic end groups increases due to the hydrolysis of the glucosidic bonds. Low pH and moisture promote this type of reaction.
The transglucosidation is considered to be a recombination of the fragments resulting from the hydrolysis with free hydroxyl groups to produce branched structures. The branching increases as the heat conversions are carried out at higher temperatures, or as the reaction time increases.
In conversions wherein yellow dextrins are prepared, there is some evidence that repolymerization of glucose or oligosaccharides into larger molecules may take place.
White dextrins may be obtained by heating acidified native starch at temperatures between 80 and 110° C. Under these conditions, the starch is hydrolyzed, as a result of which the long chain of glucose units of the starch molecule is reduced considerably. White dextrins generally have a limited cold water solubility and a limited stability of solution. After cooling, a cooked, aqueous solution of white dextrins soon sets to a paste.
Yellow dextrins are prepared at higher temperatures, viz. 150-170° C. As a result of a transglucosidation reaction, they have a more branched structure compared with the white dextrins. Further, they have a higher cold water solubility, as well as a more hydrophilic character than white dextrins.
British gums are prepared by applying heat at a relatively high pH in comparison with the white and yellow dextrins. As a result of the high temperatures employed, British gums are considerably darker in color than white dextrins.
The economics of industrial processes are favored by a constant quality of the (raw) materials used in these processes. Important parameters in this respect, concerning dextrins, are viscosity and stability of the product in solution. A significant alteration of the viscosity can have serious consequences for the performance of the process and to the quality of the end product thereof. Thus, a stable viscosity in time of a dextrin is very important, particularly when a solution of the product is to be stored over a certain, prolonged period of time. This latter aspect facilitates the utilization of dextrins as ready to use products in all kinds of formulations. Also, the flexibility, and therefore the market orientation, of the manufacturer is enhanced when the material properties of dextrin based products are not affected by using solutions of dextrins which have been kept in storage over a certain period of time. The present invention aims at providing a process for preparing a starch dextrin which is very stable, and thus has a long shelf-life.
Surprisingly, it has been found that a very stable dextrin may be prepared by dextrinizing a starch that has a very high amylopectin content. Thus, the invention is directed to a process for preparing a starch dextrin wherein a starch comprising at least 95 wt. %, preferably at least 98 wt. %, based on dry substance of the starch, of amylopectin or a derivative of said starch is dextrinized.
Not only has a process according to the invention the great advantage of leading to a dextrin which is very stable in solution and remains substantially constant in quality after a period of storage, it has been found that the preparation process requires less energy and can be effected in less time than the preparation processes of conventional dextrins. In addition, it has been found that a dextrin which has been prepared in accordance with the present invention is more stable, yet lighter in color than the conventional yellow dextrins, particularly in the form of an aqueous solution.
As has been set forth above, in accordance with the invention, a dextrin is prepared from a starch which has a very high amylopectin content. Most starch types consist of granules in which two types of glucose polymers are present. These are amylose (15-35 wt. % on dry substance) and amylopectin (65-85 wt. % on dry substance). Amylose consists of unbranched or slightly branched molecules having an average degree of polymerization of 1000 to 5000, depending on the starch type. Amylopectin consists of very large, highly branched molecules having an average degree of polymerization of 1,000,000 or more. The commercially most important starch types (maize starch, potato starch, wheat starch and tapioca starch) contain 15 to 30 wt. % amylose.
Of some cereal types, such as barley, maize, millet, wheat, milo, rice and sorghum, there are varieties of which the starch granules nearly completely consist of amylopectin. Calculated as weight percent on dry substance, these starch granules contain more than 95%, and usually more than 98% amylopectin. The amylose content of these cereal starch granules is thus less than 5%, and usually less than 2%. The above cereal varieties are also referred to as waxy cereal grains, and the amylopectin-starch granules isolated therefrom as waxy cereal starches.
In contrast to the situation of cereals, root and tuber varieties of which the starch granules nearly exclusively consist of amylopectin are not known in nature. For instance, potato starch granules isolated from potato tubers usually contain about 20% amylose and 80% amylopectin (wt. % on dry substance). During the past 10 years, however, successful efforts have been made to cultivate by genetic modification potato plants which, in the potato tubers, form starch granules consisting for more than 95 wt. % (on dry substance) of amylopectin. It has even been found feasible to produce potato tubers comprising substantially only amylopectin.
In the formation of starch granules, various enzymes are catalytically active. Of these enzymes, the granule-bound starch synthase (GBSS) is involved in the formation of amylose. The presence of the GBSS enzyme depends on the activity of genes encoding for said GBSS enzyme. Elimination or inhibition of the expression of these specific genes results in the production of the GBSS enzyme being prevented or limited. The elimination of these genes can be realized by genetic modification of potato plant material or by recessive mutation. An example thereof is the amylose-free mutant of the potato (amf) of which the starch substantially only contains amylopectin through a recessive mutation in the
Hopman Johanuddes Cornelis P.
Kesselmans Ronald Peter W.
Maas Augustinus Arnoldus M.
Brunsman David
Cooperatieve Verkoop-en Productievereniging van Aardappelmeel en
Hoffmann & Baron , LLP
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