The invention relates to the use of modified starch obtainable by treating amylose containing starch in aqueous medium with an enzyme from the group of the α-1,4-α-1,4-glucosyl transferases (EC 2.4.1.25) or an enzyme the activity of which corresponds to that of enzymes from the group just mentioned, as an agent for forming a thermoreversible gel. The invention also relates to products in the form of a thermoreversible gel having as gel-forming substance a modified starch as defined. The invention further relates to the use of a modified starch as defined in the form of an aqueous solution.
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Granular 2-nitropropyl potato starch was synthesized by reaction with 2-nitropropyl acetate in an aqueous suspension. Nitroalkylation occurs preferentially with the amylose fraction of potato starch, as was confirmed by leaching experiments and digestion of the modified starch with α-amylase. The 2-nitropropyl substituent is a mixture of the nitroalkane and nitronic acid tautomer. Some grafting occurs and to a lesser extent additional reactions (formation of carbonyls and oximes) of the nitro group take place. After catalytic hydrogenation of water soluble 2-nitropropyl starch only a small amount of the nitro functionality was reduced to the corresponding amine. Reduction of granular 2-nitropropyl starch with sodium dithionite did not go to completion and led to a complex mixture of starting material, several intermediates and side products (for example sulfamates). © 2001 Elsevier Science Ltd.
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Amylomaltases or D-enzyme (4-α-glucanotransferases; E.C. 2.4.1.25) are carbohydrate-active enzymes that catalyze the transfer of glucan units from one α-glucan to another in a disproportionation reaction. These enzymes are involved in starch metabolism in plants or maltose/glycogen metabolism in many microorganisms. The amylomaltase of the hyperthermophilic bacterium Thermus thermophilus HB8 was overproduced in Escherichia coli, partially purified and used to modify potato starch. The action of amylomaltase caused the disappearance of amylose and the broadening of the side-chain length distribution in amylopectin, which resulted in a product with both shorter and longer side chains than in the parent starch. Amylomaltase-treated potato starch showed thermoreversible gelation at concentrations of 3% (w/v) or more, thus making it comparable to gelatin. Because of its animal origin, gelatin is not accepted by several consumer groups. Therefore, the amylomaltase-treated potato starch might be a good plant-derived substitute for gelatin. ? 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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