Patent GB-813500-A (GB)
Title: Preparation of gelatinized starches
IPC: C08B30/14
Filed: 1957-10-23
Abstract: Starchy polysaccharides, as hereinafter defined, are gelatinized and dried by contacting in the presence of controlled amounts of water larger than the natural water content of the polysaccharide with a dense liquid-like suspension of turbulent solids ranging in size from 10-5000 microns, said suspension of solids being kept at a temperature high enough to gelatinize the polysaccharide.  The term "starch polysaccharide" means any ungelatinized starch or starch derivative including native starches, e.g. corn starch, potato starch and wheat flour, thin-boiling starches produced by acid modification or oxidation, dextrins, or substituted starches such as ethers or esters.  The amount of water added is preferably such as to give a total water content of the starch within the range of 30 to 90 per cent.  By addition of alkali, acids, oxidizing agents, urea and formaldehyde to the water with which the polysaccharide is moistened, the water-binding capacity of the product may be varied.  The fluidized bed may be obtained by passing an upflowing stream of gas through the solids at velocities in the range from 0.5 cm. per second to about 500 cm. per sec. or by transmitting mechanically generated oscillations to a mass of solids of proper size. Through such beds kept turbulent by oscillations, gases such as air, nitrogen or carbon dioxide may be passed, at velocities lying below the level necessary to give fluidization by the uprising gas alone.  Solids which may be used are metal balls, glass beads, beads of refractory material, enamel frit, thermostable plastic beads, sand, native starches and pregelatinized starch.  The temperature of the fluidized bed may range from temperatures just sufficient to gelatinize the polysaccharide to temperatures just insufficient to scorch the final product.  To minimize surface adhesion of the polysaccharide to the solids, the temperature in the turbulent mass should be about 20 DEG C. higher than the boiling point of water at operating pressure.  The temperature may be maintained by preheating the uprising stream of gas and by heat transfer from tubes within the bed or from outside heat exchangers.  The moist starchy polysaccharide is fed on to or beneath the surface of the bed of turbulent solids either in finely-divided condition or by dripping or spraying as a suspension. The introduction of the polysaccharide and the discharge of the product may occur either continuously or batchwise.  Depending on the particle size, the product may float on top, or sink to the bottom, of the bed or may be entrained in the rising gas stream.  When no separation occurs and the product is dispersed through the bed it may be recovered by screening. The temperature may be regulated to keep drying to a minimum while the outer layer of the polysaccharide particle is gelatinized and then raised to complete gelatinization and drying.  The procedure may be effected stepwise using two or more fluidized beds at different temperatures.  In examples, (1) potato starch suspended in water is sprayed continuously on to a bed of sand (400 microns) fluidized by air at 20-25 cm/sec. at 200 DEG  C., whereby dry starch floats to the top and is withdrawn through an overflow; (2) cassava starch suspended in water is sprayed continuously on to the bottom of a bed of metal balls (400 microns) fluidized by air at 80 cm/sec. and heated to 160 DEG  C., whereby the dry starch is entrained in the air stream and recovered by a cyclone; (3) potato starch suspended in water is sprayed on to the surface of a bed of pregelatinized potato starch (less than 40 mesh) fluidized with a gas velocity of 4 cm./sec., solids leaving the reactor through an overflow are screened and the massive starch particles are dried separately at 110 DEG  C.; (4) suspensions of potato starch containing 60 per cent moisture are acidified with HCl to pH 4.5, 3.8 and 3.0 and treated as in (1); (5) a suspension of thin-boiling corn starch containing 55 per cent moisture is sprayed on to a bed of ground pregelatinized thin-boiling corn starch fluidized in a stream of gas at 90 DEG  C. and a mixture of starch grains and bed material is withdrawn continuously and screened; the fine fraction consisting of bed material is recycled to the first bed and the coarse partlygelatinized starch is subjected to further treatment in fluidized sand beds at 105 DEG  and 120 DEG  C. kept turbulent by mechanical oscillations and the mixture of sand particles and starch granules which is continuously discharged from the bed is separated and the sand recycled; the starch product is ground and separated into a coarse fraction, which is recycled for regrinding, and a final product of ground pregelatinized thin-boiling corn starch; (6) cassava starch with a moisture content of 40 per cent is supplied in a finely-divided state to a turbulent bed of pregelatinized cassava starch at 90 DEG  C. for an average contact time of 15 minutes; natural cassava starch may also be used as the bed material.