White dextrins

Dextrins (white dextrin) are prepared by heating starch, which has been moistened with a small quantity of dilute nitric acid and dried at 110-120 °C. Dextrin may contain up to 15% soluble starch. Yellow dextrins are more completely decomposed and, unlike the white variety, they contain appreciable amounts of maltose which may be detected and estimated by their reducing power. 

The white dextrins are the least soluble in cold water, the insoluble part consisting of soluble starch and of more or less marked proportions of organic (cellulose, gluten, etc.) or mineral impurities (sand). 

Dextrins (pyrodextrins) are made by heating dry starch with or without acid. Since it is a dry process, recovery of water-soluble materials is simpler than with aqueous fluidity and oxidized starches. Depending on reaction conditions, greater or lesser amounts of three reactions will occur (a) hydrolysis (b) transglycosidation and (c) repolymerization. According to which predominates, the product is a white dextrin, a yellow dextrin or a British gum. Like other converted materials, these products offer a way to use higher solids to increase performance. 

Commercial dextrins are specifically the oligomers of starch. White dextrins, so called because of their visual appearance, are produced from a 30-40% suspension under the mildest possible hydrolysis conditions (79-120°C for 3-8 h in 0.2-2% H2S04 or HC1). Yellow dextrins and British gums are the partial hydrolysates at higher time-temperature integrals. Maltodextrins, dextrose equivalent20 5-19, derive from controlled enzyme or acid partial hydrolysis of gelatinized corn starch. The 20-24 dextrose equivalent hydrolysates tire com syrups (Appi, 1991). 

Adhesives for Miscellaneous Uses. Starch is also used to prepare children s library paste. A blend of low-soluble white dextrin and unmodified cornstarch is cooked up with glycerine and water to about 55% solids and set back to obtain a firm but smooth texture (6). Cornstarch is also used in the production... 

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. 

In dry form white dextrins are white to off-white in appearance, and when compared to powdered starch, their dispersion time in water is greater. (Smooth suspensions can be developed in room temperature water if good agitation is used.)... 

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. 

Dextrin.—Dextrin is a carbohydrate made from starch (chiefly from corn or potato starch) by the application of heat (yellow dextrin) or by treatment with both heat and acids (white dextrin). It forms a paste with water, the yellow variety tending to swell up and dissolve much more readily than the white. When examined microscopically in alcohol mounts, the grains, while conforming in general outline to those of the type of starch from which the dextrin was prepared, nevertheless show more conspicuous striations and clefts.. Corn dextrin shows distinct striations, whereas striations Digitized by Microsoft ... 

Avedex British gum Caloreen canary dextrin C Pharm Crystal Gum dextrinum album Primogran W starch gum yellow dextrin white dextrin. 

About fifteen years later. Greenwood classified only three groups of dextrins A) white dextrins prepared finrm starch in the presence of an acid... 

On the other hand, Acton accepted the definition that British gums are products of heating of starch either alone or with a basic catalyst. Additionally, many technicians understand British gums to be the products prepared with catalytic amounts of acids. In this situation, the classification of dextrins in accord with some selected physical properties should be given priority. It parallels, to a certain extent, the foregoing classifications as, for instance, the solubility of white dextrins ranges from 1 to 95%, and their water uptake is described by a ratio of dextrin to water of 1 1 to 1 5. Yellow dextrins are water-soluble to the extent of 95 to 100%, and their water uptake is 1 1.5 to 1 0.75, and even less. British gums resemble white dextrins in their solubility, but simultaneously they form more-viscous solutions. 

The physical properties of pyrolyzed starch obviously vary, depending on the conditions applied in the process. The appearance of white dextrins and... 

Acid catalysts certainly favor hydrolysis, at least in the first stage of dextrinization. The (1 — 6) bonds are disintegrated, and shorter chains are formed from (1 - 4) intermolecularly bonded D-glucosyl units. This corresponds to the formation of white dextrins (8). However, it was noted that... 

White dextrins, formed when starch is heated at low temperatures (79-120°) in the presence of acid catalysts, usually hydrochloric acid, for short times (3-8 hr.). Under these conditions, no color develops in the product. 

The thermal treatment causes changes in solubility, viscosity, and alkali-lability, and the extent of modification increases in the order White dextrins < Yellow dextrins < British Gums. 

In the case of the White dextrins, pyrolysis induces an apparent hydrolytic reaction, because, with time, there is a steady increase in reducing power and cold-water solubility and a steady decrease in viscosity. These characteristic changes are shown in Fig. 1. Pastes made from such dextrins show gelation, or set-back, properties comparable to those of the original starch. 

Fig. 1.—Formation of a White Dextrin from Corn Starch Changes in (1) Viscosity, in Centistokes, (2) Alkali Lability, and (3) Solubility, %, as a Function of the Conversion Time. (Redrawn from Ref. 5.)...

White dextrin. Hydrolyzed at low temp for short period of time in the presence of large amts of acid, Whire color. Odorless. Slightly sol in cold water giving a red color with iodine. Very sol in hot water giving a blue color with iodine,... 

Manufacturing Condition White Dextrins Canary Dextrins... 

Dextrins are the product of dry-roasting starch in the presence of an acid catalyst. Although potato, tapioca, and sago starches are the easiest to convert to dextrins, the low cost and ready availability of cornstarch, make it the most commonly used starch. Dextrins are generally divided into three categories white dextrins, canary or yellow... 

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