Patent GB-787026-A (GB)
Title: Improvements in or relating to process of making a stable phosphate derivative of starch
IPC: C08B31/06
Filed: 1954-07-01
Abstract: A stable starch phosphate ester product containing mono-starch phosphate and/or di-starch phosphate groups is obtained by heating a starch product containing 5 to 20 per cent of moisture in contact with an inorganic phosphate at a pH of between 4 and 11.5 and at a temperature and for a time sufficient to effect the desired degree of esterification, said phosphate being selected from the group consisting of metaphosphates, polymetaphosphates, pyrophosphates, tripolyphosphates and mixtures thereof, and said heating being carried out while permitting the evaporation of moisture.  The process is applicable to any starch, e.g. corn, wheat, grain, or sorghum starch in raw or modified form and in gelatinized or granular form, thus thin boiling starches, dextrins and derivatives such as starch ethers or esters (other than phosphate esters) may be used. At lower pH values within the stated range the products are generally mono-starch phosphate esters while at the higher pH values cross-linked esters are formed.  Thus at pH of 4 to 5 metaphosphates form substantially only the mono esters and above these values a larger proportion of di-starch phosphate esters (i.e. cross-linked esters is formed. The pH values for the formation of simple esters when polymetaphosphates, pyrophosphates, and tripolyphosphates are used are preferably from about 7 to 9 whereas with pH values of about 9 to 11.5 the cross-linked esters are formed to a much greater extent.  The pH may be increased by the addition of alkaline substances such as sodium-carbonate, -bicarbonate, -orthophosphate, or -hydroxide.  In carrying out the process the phosphate salt reagent is first mixed with the starch, e.g. by adding the phosphate to an aqueous starch slurry at room temperature, stirring the slurry, and then filtering.  The moisture content of the starch is then adjusted to within the range of 5 to 20 per cent and if it is desired to keep the starch in unswollen granule form the starch-phosphate salt mixture may be dried in typical starch driers, e.g. using heated air at temperatures of from 120 DEG  to 255 DEG  F.  Alternatively, a slurry of starch in an aqueous solution of the phosphate reagent may be spray dried and the starch may or may not be gelatinized during this spray-drying operation.  The next step is to heat the resulting starch-phosphate salt mixture and this step should be carried out at about 100 DEG  C. to about 160 DEG  C. and for a period of time which will vary according to the type of product desired. The degree of cross-linking increases as the time and temperature of the heat treatment increases but is primarily influenced by pH control appropriate to the type of phosphate reagent employed. The amount of phosphate salt reagent admixed with the starch during the heat treatment is preferably about 2 to about 10 per cent (calculated on the anhydrous salt), based on the dry weight of the starch and the pH of the mixture as measured on a 20 per cent aqueous dispersion of the mixture using a glass electrode should be between 4 and 11.5 depending on the particular type of phosphate reagent employed and on the reaction to be promoted. After the heat treatment the starch ester may be washed in appropriate solvents and dried.  The preferred products are those having up to 0.1 orthophosphate group per anhydro glucose unit and the products will be water-soluble or water-insoluble depending on the degree of phosphonylation and the manner of treatment.  In examples: (1) to (3) corn starch is reacted with sodium metaphosphate at 120 DEG  C. under varying pH conditions, ranging from acidic to alkaline; (4) corn starch is reacted with sodium tripolyphosphate for one hour at 120-130 DEG  C; (5) as in (4) except that the reaction is effected for two hours at 120 DEG  C.; (6) and (7) corn starch is reacted with different amounts of sodium tripolyphosphate at 120 DEG  C.; (8) grain sorghum starch is reacted with sodium tripolyphosphate at 120 DEG  C.; (9) acid-modified thin boiling corn starch is reacted with sodium tripolyphosphate using various amounts of the latter, the process being carried out by adding the starch with stirring to an aqueous solution of sodium tripolyphosphate, filtering, air-drying the filter cake to a moisture content of about 12 per cent and then heating for one hour at 120 DEG C. to form the starch phosphate.  A comparative example is also given in which the heating step at 120 DEG  C. is omitted and a table is given to show that in this case the characteristics of the starch are not materially altered; (10 and (11) corn starch is reacted with sodium hexametaphosphate, and tetrasodium pyrophosphate respectively at 120 DEG  C.; (12) corn starch is reacted with a combination of sodium tripolyphosphate and sodium metaphosphate at 120 DEG  C. to give a mono-corn starch phosphate ester cross-linked with di-starch phosphate groups.  The starch phosphate products may be used for the thickening of food products, in gum drop candy manufacture, in drilling muds and as sizes, e.g. in sizing paper pulp and in the finishing of cotton, woollen and synthetic fibre fabrics (see Groups V, VI, VIII and XXI).  German Specification 644,027 and U.S.A. Specification 2,252,479 are referred to.ALSO:A starch phosphate ester containing monostarch phosphate and/or di-starch phosphate groups obtained by heating a starch, modified starch, e.g. dextrin, or a starch derivative, e.g., a starch ether or ester (other than phosphate ester), particularly corn starch, with an inorganic phosphate selected from metaphosphates, polymetaphosphates, pyrophosphates, tripolyphosphates and mixtures thereof (see Group IV(b)) may be used in sizing paper pulp and textiles.ALSO:A starch phosphate ester containing monostarch phosphate and/or di-starch phosphate groups obtained by heating a starch, modified starch, or starch derivative, e.g. a starch ether or ester (other than phosphate ester) with an inorganic phosphate selected from metaphosphates, polymetaphosphates, pyrophosphates, tripolyphosphates and mixtures thereof (see Group IV (b)) may be used for the thickening of food products, e.g. soups, canned vegetables or fruits, or may be used in gum drop candy manufacture where they are relatively stable to the action of sugar and citric acid at high temperature, or in salad dressings where they are relatively stable to the action of sugar, acetic acid and heat. In an example for preparing a pudding mixture, an aqueous slurry is prepared containing a starch phosphate (obtained by reacting grain sorghum starch with sodium tripolyphosphate for 1 hour at 120 DEG  C.), sucrose, flavour mix, sodium chloride, and monostearin and the slurry is then heated in a spray drier to gelatinize the starch and dry it to a powder which is then dry blended with dextrose, sucrose, vanilla colour mix, imitation vanilla sugar, sodium chloride, rennin, calcium acetate, and imitation butter. The mixture is then ground and stirred into cold milk (62 DEG F.) to form a homogeneous pudding mixture.  In another example, a starch phosphate made by reacting corn starch with a combination of sodium tripolyphosphate and sodium metaphosphate at 120 DEG  C. for one hour is made into a slurry with water and this is added to a batch of cooked cherries prepared by stirring a mixture of drained cherries, cherry juice, sucrose, corn syrup, and artificial colour while cooking to 190 DEG  F.  After the addition of the starch phosphate slurry the temperature is raised to and held at 196 DEG  F. for ten minutes and the mixture poured into cans which are then sealed, held in boiling water for 10 minutes and then cooled to room temperature.  An example is also given in which a corn starch phosphate obtained by reacting corn starch with sodium tripolyphosphate for one hour at 120-130 DEG  C. is used in canning sweet corn (cream style).