Starch is extensively used in the food industry, not only for its energy content (carbohydrates), but also as a thickening or stabilising agent. Native starches, however, require pre-treatment in order to have the required thickening and similar properties in situ. Starches modified by chemical crosslinking, such as phosphate crosslinking, have the required in situ properties, such as shear, acid and heat resistance. However, consumers more and more demand the use of chemical-free ingredients in food, even though some chemical modifications are regarded as safe.
U.S. Pat. No. 6,221,420 (EP0721471) discloses a thermally inhibited starch, i.e. a hydrothermally modified starch which is inhibited from returning to its native state. The product is obtained by dehydrating starch to a water level below 1%, followed by heat-treating the dry starch at about 140° C., in a fluidised bed. U.S. Pat. No. 5,641,349 and U.S. Pat. No. 6,010,574 disclose similarly. Alcohol may be used to aid drying, but otherwise does not play any active role in the inhibition process.
EP 1799719 discloses a process for producing resistant starch by acidifying starch at 3% moisture to a pH 2.3 in the presence of about 4% of ethanol followed by heating at 140° C. This treatment is reported to result in 57% resistant starch. Lower and higher levels of ethanol result in a lower yields of resistant starch.
Thus, there is a need for providing hydrothermally modified starches with improved visco-stability and for processes for producing them in a more economical way, especially where equipment requirements are concerned.