Conversions dextrins

After 30 hours, the maximum and critical fermentation is underway and the pH must remain above 4.0 for optimal fermentation. However, accompanying bacterial contamination from various sources such as yeast contamination, improper cleaning procedures, slow yeast growth, or excessive temperatures can result in a pH below 4.0. The remaining amylase enzymes, referred to as secondary conversion agents, are inactivated and can no longer convert the dextrins to maltose. Under these circumstances, the fermentor pH continues to drop because of acid production of the bacteria, and the pH can drop to as low as 3.0. The obvious result is a low ethanol yield and quaUty deterioration. 

The importance of time, temperature and acid concentration in the hydrolysis of cellulose with dilute acid was recognized by early investigators and applied in the investigations of Simonsen in 1898. Further study was made by Kressman and reported in U. S. Department of Agriculture Bulletin No. 983. Reviews of the quantitative aspects have been made by Doree. Liiers pointed out that the conversion of cellulose dextrin to D-glucose by dilute sulfuric acid was a monomolecular reaction. The constants of the hydrolysis of wood cellulose have been determined by Saeman. The reaction rate (A ) was found to be expressed by the following equation ... 

When production volume is sufficient, it is economical to build one plant for one product. Batch production in a single unit may be limited by maximum reactor size. Holdups of greater than 20,000 gal are handled in separate parallel reactors. To use common upstream and downstream facilities, the reactors may not be operated simultaneously but on overlapping schedules. When long reaction times cannot be avoided, the reaction sections operate batch wise however, feeding reactants and recovering products may be continuous for economic reasons. This practice is typical of many processes, such as the saponification of natural fats in intermediate quantities. In the production of ethanol by fermentation, two reactions (saccharification and fermentation) are operated on a batch basis, while hydrolysis (conversion of starch to dextrin) and product recovery by distillation are continuous. 

Dextrinization of tapioca starch is well-known. The difficulty in dextrinizing corn starch,64 and the relative ease of tapioca starch conversion,65 have been described. The near-absence of lipids, which interfere with the dextrinization process, has given tapioca dextrins an advantage in stability and color because of their ease of manufacture and control. However, the economics of base starch supply have resulted in a significant shift to waxy com starch as a base for industrial dextrins, even though... 

Dextrins are produced by dry heating (roasting) starch in the presence of an acid catalyst. They are produced in a range of viscosity and color specifications. Dextrins are primarily used as adhesives in paper conversion, such as laminating and envelope production. A low-viscosity dextrin is used in Europe as a total chlorine free (TCF) coating binder for application on TCF paper. 

In a maltodextrin process using enzyme-catalyzed conversion, the starch slurry (30% to 40% dry solids) is first pasted at a temperature of 80-90°C, and is then treated with a heat-stable bacterial alpha-amylase for liquefication. When stabilized with calcium ions, alpha-amylases from B. licheniformis or B. stearothermophilus can withstand temperatures of 90-105°C for at least 30 minutes,10 allowing sufficient process time to split the 1,4 bonds and form maltose and limit dextrins (see Chapter 7). 

Add 0.5 ml of the bacterial amylase solution to 50 ml of the 20 g 1 1 nonbuffered starch solution prepared in Step 1. Periodically place a few drops of the reaction mixture on a glass plate and add one drop of the iodine reagent. The color should finally turn red, indicating the total conversion of starch to dextrin. This liquefaction step should last for approximately 10 min. 

Ge Y, Wang Y, Zhou H, Wang S, Tong Y, Li W (1999) Coimmobilization of glucoamylase and glucose isomerase by molecular deposition technique for one-step conversion of dextrin to fructose. J Biotechnol 67 33 10... 

Liquidification of starches for free flow Recovery of sugar from candy scraps Remove starches to increase sparkling properties Remove starches to increase sparkling properties An aid in preparation of pectin from apple pomace Conversion of starches to low molecular weight dextrins (corn syrup)... 

Photolysis of chlorpromazine (1). The photolysis of 1 results mainly in oxidation to the corresponding sulfoxide. Irradiation in the presence of a cyclodextrin (CD), however, results mainly in dechlorination to promazine (2), which is also converted into a sulfoxide, (3), on photolysis. The rate of conversion of 1 to 2 depends on the cyclodextrin used, the rates following the order /3-cyclodextrin >y-cyck)dextrin> a-cyclodextrin. Since these cyclodextrins differ in the size of the cavity, it appears that the conversion of 1 to 2 takes place within the inclusion complex. ... 

STADEX Dextrins are partially hydrolyzed starches that are prepared by heating or dry roasting starch in the presence of an acid catalyst. The conversion process - the change from starch to dextrin - changes the properties of the parent starch in several ways. Notably, the dextrin exhibits a thinner cooked-paste viscosity, an increased cold water solubility, and a color change from white to off-white or yellow. 

The product classification covering white dextrins includes a large number of products and a broad range of properties. It is generally marked by extremes of conversion from those that are only lightly converted to those that approach the very highly converted character of the canary dextrins. 

When cooked, fresh pastes are light to dark buff in appearance, depending upon the degree of conversion. As the pastes cool to room temperature they turn opaque, becoming nearly white. Low conversion white dextrins have little viscosity stability, and when cooled, thicken or set-back to form soft gels. By contrast, high conversion white dextrins cook-up to form pastes that congeal less, are more fluid, and exhibit better viscosity stability. 

Even if a strong secondary conversion of the dextrins has occurred and the total yield of limit dextrins is low, these dextrins will contain a great deal of the phosphorus content of the original starch. This is demonstrated by the data of Table XVIII. 

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