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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Native potato starch is an excellent carrier of minerals due to its inherent ion exchange capacity. Mineral enrichment not only changes the nutritional value but also influences starch pasting and swelling properties. Hydrothermal treatments like annealing constitute a straightforward and green way to tune functional properties. Here, novel combinations of mineral enrichment and annealing were studied. Ion exchange was readily achieved by suspending starch in a salt solution at room temperature over 3 h and confirmed by ICP-OES. Annealing at 50 °C for 24 h using demineralized water or salt solutions strongly affected pasting, thermal, and swelling properties. The obtained XRD and DSC results support a more ordered structure with relative crystallinity increasing from initially 41.7% to 44.4% and gelatinization onset temperature increasing from 60.39 to 65.94 J/g. Solid-state NMR spectroscopy revealed no detectable changes after annealing. Total digestible starch content decreased after annealing from 8.89 to 7.86 g/100 g. During both ion exchange at room temperature and annealing, monovalent cations promoted swelling and peak viscosity, and divalent cations suppressed peak viscosity through ionic crosslinking. The presented combination allows fine-tuning of pasting behavior, potentially enabling requirements of respective food applications to be met while offering an alternative to chemically modified starches.
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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