Vergleichende Kernresonanzuntersuchungen der Wasserbindungsverhältnisse von Stärke und rohen Kartoffelstücken während der Trocknung

Comparative NMR-Investigations of the Binding of Water in Starch and Raw Potatoes During the Drying Process. A reversible swelling which is caused partly by reorientational motion of water is observed by heat-moisture-treatment of native starch at 60°C. This means that water can either only loosen the outer amylopectine layer or that it gets through to the inner part of a starchgranule to become less loosely associated with amylose. Obviously this behaviour is important during hot-air-drying of potatoes. The drying-up of the outer layers of the material to be dried means a reduction of the self-diffusion-coefficient and a hindrance to the discharge of water. But apart from this another influence upon the drying-speed is observed which is in direct connection with the behaviour of starch already mentioned above. Soon at the beginning it is to be noticed that the mobility of the water within the cell increases and that it gets transported into the middle of the potato. At a temperature of 50°C to 60°C the swelling of starch starts and water therefore becomes immobilized. To some extend some water becomes enclosed in existing structures where it remains relatively flexible. These processes can be followed by nuclear-magnetic-resonance (NMR-Spectroscopy). On this basis statements about different water-molecules and their particular quantities can be made. The immobilisation of the water can be shown by the smaller water activity of the starch samples after the heat-moisture-treatment. Also it can be seen in the lowering of the drying speed.