| Abstract: | Models for the Structure and Properties of Starch. Regularly-shaped model substances may be helpful to get insight in starch properties. Suitable compounds are prepared by phosphorolytic synthesis with free maltooligomers as primers and maltooligomers coupled to a support leading to linear and different types of branched products carrying amylose chains of uniform length. In the first part of this paper, the influence of chain length, chain length distribution and density of branching on solubility, retrogradation and gel formation is discussed more generally. Interest is focused on conclusions which may be derived for the special role of the natural starch components. The second part reports on studies with pure maltooligomers which extend results from the synthetic models into the short-chain region. X-ray powder patterns of samples precipitated from aqueous solution gave the B-type in the range DP 20 to 13, and the A-type in the range DP 12 to 10. A limit for retrogradation and crystallization is obviously DP 8 to 9. With the pure compounds the C-type is not observed. Results indicate that the x-ray type of different starches may be related to the length of the outer branches of amylopectin emerging from the cluster regions. – In the presence of amylose I3- ions are slowly formed from an iodide-free iodine solution. Corresponding studies with the series of maltooligomers show a close correlation between the extent of I3 formation and the tendency for helix formation as anticipated. Remarkably, maltotriose was found being equally active as α-cyclodextrin indicating that both substances are quite similar in their conformation in aqueous solution. |
