Yellow 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. 

External Characters.—The colour, odour and taste are to be noted. White or yellow dextrins are mostly prepared by means of acid (hydrochloric acid tends to give a reddish and nitric acid a greyish tint), whereas brown dextrins are those obtained by direct torrefaction without acid. 

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). 

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. 

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. 

Some pretreatments of starch, such as suspending in water to form a gel, followed by drying, also influence the course, but not the result, of dextrini-zation (see Fig. 9b). Similarly, the course of dextrinization is different in the case of so-called hydrogen starch, which is monostarch hydrogenphos-phate (amylophosphoric acid). In the case of farina yellow-dextrins, a solubility of close to 100% is reached within the first hour of the process. The solubility of dextrins also depends on the temperature applied. Accord-... 

Almost all authors discussing the topic agree with one another that the viscosity of dextrins decreases quite suddenly in the first hour of dextrinization, to achieve an almost flat curve on further roasting. This is the case for British gums, as well as for acid-catalyzed dextrinization. A slight increase of viscosity is noted in the case of materials roasted for over 3 h at temperatures above 200°. This may be due to secondary polymerization of degradation products. On the other hand, the viscosity of yellow dextrins from com... 

O-a-D-glucopyranosyl-D-glucose (panose) was found. Graefe cited structures of yellow dextrins having (1 6)-fi- and (1 — 6)-a-D-glucosidic... 

Some attention has been paid to the role of various salts as catalysts. These studies were performed by Bryce and Greenwood in order to establish the effect of the addition of 2% of various salts on the decomposition of amylomaize starch at 223 to 337 ° into carbon mon- and di-oxide and water the results will be discussed in Section VI. Manganese(II) chloride in the presence of nitric acid, or aluminum salts should be mentioned as catalysts for starch dextrinization. Aqueous solutions of various salts depo-lymerize starch granules at room temperature. The anions of these salts have a more pronounced effect than the cations. Russian workers developed studies on dextrinization in the presence of either alkalinized or acidified alum they obtained either white or light-yellow dextrins of high quality... 

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. 

However, for the Yellow dextrins, although the viscosity again decreases with increase in conversion time, the alkali-lability passes through a maximum (see Fig. 2). This must indicate that some complex transglyc-osidation and repolymerization reactions occur at later stages in the process. 

In the literature, there are few data for the British Gums, but it is likely that the reactions that take place are comparable to those for the Yellow dextrins. ... 

Fig. 2.-—Formation of a Yellow Dextrin from Com Starch Changes in (1) Viscosity, in Centistokes, and (2) Alkali Lability, as a Function of the Conversion Time. fRe drawn from Ref. 5.)...

Canary dextrin, yellow dextrin. Hydrolyzed at high temp for long period of time in the presence of small amts of acid. Light brown to yellow color, slight odor. Low viscosity very sol in cold water. 

Yellow dextrin. See Dextrin Yellow ferric oxide. See Ferric oxide Yeiiow Fonoiine . See Petrolatum... 

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