The invention pertains to a method for oxidizing a
starch into a
dialdehyde starch using orthoperiodic acid, comprising: a) reacting an
aqueous solution of orthoperiodic acid with dry
starch or a
starch slurry, having a starch content of 35 - 85 wt%, in a
molar ratio of
periodic acid : starch (in AGU) of 1:1 - 1:4, at a temperature below the
starch gelatinization temperature and for a time less than 3 hours and at a pH < 1.0, at a starch concentration generally in the range of 5 - 27 wt%, based on the weight of the mixture of orthoperiodic acid and starch, wherein the starch that is brought into contact with the orthoperiodic acid is provided in an amount which complies with the following formulas: (i) starch concentration (wt%) ≤ -0.2 * DoO + 34%, and (ii) starch concentration (wt%) > -0.2 * DoO + 25%, wherein DoO is 25, 50, 75 or 100%, b)
dewatering and displacement washing, wherein the
molar ratio of orthoperiodic acid : starch is selected to obtain a
dialdehyde starch with a desired degree of oxidation [DoO] between 25 and 100%, wherein the
molar ratio of orthoperiodic acid : starch is selected according to %DoO = 100*(molar ratio
periodic acid:AGU). The invention also pertains to a
dialdehyde starch obtainable by the above method, with a degree of oxidation of at least 75%, and with a
iodine content of less than 100 ppm.