Dextrin can be bought, but it is very easy to make.
Cornflour when heated to the right temperature changes to dextrin - it's that simple.
My method is to put a 1/2" layer of cornflour in a metal baking tray and place it in a hot oven (200 degrees Centigrade) for about 2 hours. Stir it around every 1/2 hour or so to ensure it's all cooked.
After 2 hours, it should have changed from white to light yellow. If it goes brown or black, the oven is too hot!
A little experimentation may be required until you have got a good idea of the temperature of your oven - they do vary.
In theory if you add a little of your product to some water with a crystal of iodine in it, it should not turn blue. This is a test for starch, and all the starch should have been converted to dextrin.
In practice I have never bothered with this and the dextrin has done it's job perfectly.
Yellow dextrins are used as water-soluble glues in remoistable envelope adhesives and paper tubes, in the mining industry as additives in froth flotation, in the foundry industry as green strength additives in sand casting, and as binders in gouache paint.
White dextrins are used as:
* as crispness enhancer for food processing, in food batters, coatings and glazes,
* as textile finishing agent to increase weight and stiffness of textile fabrics,
* as thickening and binding agent in pharmaceuticals and paper coating formulations.
As pyrotechnic binder and fuel, they are added to fireworks and sparklers, allowing them to solidify as pellets or "stars."
Due to the rebranching, dextrins are less digestible; indigestible dextrin are developed as soluble fiber supplements for food products.
Dextrin added to water forms a sticky gum used as a food thickener.
White and yellow dextrins from starch roasted with little or no acid is called British gum.