British Gum Dextrin

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. 

Starch pyrodextrins and British gums have the abiUty, in aqueous dispersion, to form films capable of bonding like or unlike materials. Thus, they have uses as adhesives for envelopes, postage stamps, and other products. These dextrins are used in glass-fiber siting to protect the extmded fiber from abrasion, and as binders for metal core castings, water color paints, briquettes, and many other composite materials (qv). 

Britischgummi, n. British gum, dextrin, Brockchen, n. small bit, small piece, crumb, brockelig, a. brittle, friable, crumbly, fragile. Brdckeligkeit, /. brittleness, friability, brbckeln, v.t. crumble. 

BRITISH GUM. — Artificial Gum—Torrefied Starch—Dextrin,—Under theso names a modification of stsroh Is known, which is often prepared in the following manner —... 

British gum or dextrin is now mot with in commerce in three distinct forms namely, as a white, brilliant, and pearly powder as a sirapy solution and in the form of exotic gum, in greater or less perfection, either broken into small fragments, or made into rolls of various sizes. 

The last-named authority has remarked with reference to British gum prepared by sulphuric acid, that it possesses the disadvantageous property of being deliquescent. This method is, therefore, never employed, as besides this, the products are often colored. He also states that when nitric arid is employed in the preparation of dextrin, it must be perfectly pwe. Commercial nitrio acid, as obtained by the action of oil of vitriol upon nitrats of Soda, always contains a small amount of chlorine and although this element is contained in diminished proportion in the dextrin, it is nevertheless sufficient to considerably lessen the brilliancy of the colors prepared with the dextrin. Several printers upon paper and vegetal tissues have observed this, but have been unable to account for it otherwise than by attributing it to the iaferior quality of the gum. 

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). 

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

Chemistry of Dextrinization, and Structure of Dextrins and British Gums 302... 

The common name dextrin was given in 1833 to the gum that resulted from treatment of starch with sulfuric add. This name is attributable to the direction of the optical rotation of the product. - The products of starch d radation by purely thermal processes arc called British gums, as they were acddentally discovered after a fire in Dublin, Ireland, destroyed a building having potato starch stored within it. The truth of this story is sometimes questioned, and it may be apocryphal, as there is no account of this fire in the Dublin newspapers of that period. ... 

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. 

Commercial dextrins and British gums are mone-or-less water-soluble, and form colloidal solutions, usually yellow or brown, that are more colored than the solid matter. After evaporation of these solutions, a sticky, elastic residue is obtained. Dextrins are practically odorless, except those originating from potato starch. The unpleasant odor of the latter products can be masked by addition of Bergamot oil. ... 

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... 

Further chemical changes that occur during dextrinization should be discussed separately for the case of formation of British gum, and for variously catalyzed thermal processes. Thus, when starch (1) is heated in the presence of moisture, random hydrolytic scission at the (1 - 6), and more readily at the (1 — 4), linkages has been proposed to occur in the branched chains of amylopectin, to give more-linear structures, leading to the observed decrease in viscosity. o-Glucosyl oxocarbonium ions (2) were postulated as intermediates, but free radicals (3) formed by homolytic fission at the (1 4)-glycosidic bond are also feasible. 

Transglycosylation seems to be the most typical and predominant reaction among the group of reactions constituting the dextrinization process. The evidence for it, as well as for the mechanism just presented, was provided by the results of methylation analysis of com British gum (see Table XIX). Incidentally, the formation of ether-type bonds was questioned. ... 

XX and XXI) it revealed differences between the results for pyrodextrins obtained in the presence of an acid catalyst and for British gums. If the problem of roasting of starch in the presence of a catalyst is to be discussed in detail, dextrinization under the influence of acids, alk s, and oxidants must be considered separately. 

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