GB812339A - Improvements in or relating to process for the preparation of starch phosphates - Google Patents

Abstract

An alkali metal starch phosphate is prepared by commingling starch with an aqueous solution containing at least one orthophosphate salt of an alkali metal, e.g. lithium, sodium or potassium, and having a pH between 3.0 and 7.5, contacting said starch and said solution in a proportion and at a phosphate concentration and for a time sufficient to incorporate said orthophosphate in said starch in an amount equivalent to at least 1.0 per cent by weight of phosphorus, removing unabsorbed liquid from the treated starch, and heating the treated starch at a temperature between 120 DEG and 175 DEG C. for a period of 1 to 15 hours. The heating is carried out either at atmospheric pressure or under vacuum. The aqueous solution of orthophosphate salt is prepared by dissolving an alkali metal phosphate salt such as monosodium phosphate or disodium phosphate, or a combination of monosodium and disodium phosphate, in water in such a proportion that the resulting solution has the desired pH. The phosphate salt may also be formed in situ either by dissolving a basic phosphate, such as trisodium phosphate, in water and adjusting the pH with phosphoric acid, or by neutralizing an aqueous solution of an acidic phosphate salt or phosphoric acid with an alkali metal hydroxide. In a preferred procedure, 3 to 4 parts of starch are treated with 5 to 8 parts of solution containing between 2.5 and 30 per cent concentration of phosphate and having a pH between 3.0 and 7.5, preferably between 5.5 and 7.5, the resulting slurry is agitated for at least 5 minutes, the starch granules are separated from the solution, e.g. by filtration, and excess surface moisture is removed, for example by drying in air or by heating at a temperature below the gelatinization point of starch. The resulting granules, containing 8 to 15 per cent moisture, are then heated at 120 DEG to 170 DEG C. for 1 to 15 hours. Generally 4 hours is sufficient at a temperature between 130 DEG and 155 DEG C. The process is applicable to root starches, such as potato starch, or cereal starches, such as corn starch, and wheat starch. Starch phosphate films may be cast from cooled solutions of the phosphates. The products are also useful as sizing agents in the surface finishing of paper, as beater additive in paper making, as a water loss inhibitor in oil well drilling muds, as a core binder in foundry cores and as a thickening agent in food products. Detailed examples are given. Specifications 812,340 and 812,363 are referred to.ALSO:Alkali metal starch phosphate, useful as a thickening agent in food products, such as soups, ice cream, puddings, mayonnaise, salad dressings and pie fillings, is prepared by mixing starch with an aqueous solution of at least one orthophosphate salt of an alkali metal, e.g. lithium, sodium or potassium, at pH 3-75, removing unabsorbed liquid from the starch and heating it at 120-175 DEG C. for 1 to 15 hours. Specifications 812,340 and 812,363 are referred to.