Self-Assembly of Starch Spherulites as Induced by Inclusion Complexation with Small Ligands - Food Colloids: Self-Assembly and Material Science - page 125

titration, DSC and light microscopy. The degradation of starch at the molec-
ular level led to a decrease of the iodine-binding capacity, and the rate of starch
degradation was lower for complexed starch compared with the reference. In
the micrometre range, the disintegration of the spherulites was seen by micros-
copy, although remnants of the supramolecular assemblies could still be
recognized after an incubation time of 24 h. Interestingly, the melting temper-
ature T m and the melting enthalpy DH of amylose-g-nonalactone complexes
were found to increase with enzymatic treatment. These results indicate that at
low a-amylase activity the complexes are not completely degraded. By analogy
with amylose lipid complexes, it can be assumed that ordered helical segments
are less susceptible towards enzymatic degradation than the amorphous
regions. 20 The DSC results suggest that a partial degradation of starch con-
tributes to a higher mobility of the polymer, which in turn contributes to the
formation of more stable crystallites at the expense of less stable ones. This
means that a slight enzymatic hydrolysis of starch complexes may increase the
thermal stability of the remaining complexes, but at the same time it induces
partial disassembly of the spherulites. 16 It can be hypothesized that an enzyma-
tic annealing of spherulites in combination with a thermal annealing treatment
is a promising route for preparing spherulites with increased molecular order.
8.4 Concluding Remarks
The specific interaction between starch and small molecules capable of inducing
the formation of helical amylose complexes can promote the self-assembly of
complexed amylose into spherulitic structures. The formation of spherulites can
be viewed as an interaction that drives amylose out of solution, promoting
solid liquid bulk phase separation, since the helical segments have a strong
tendency to associate. The formation of partly crystalline spherulites can be
controlled by the type and the concentration of the ligands, the temperature/
time conditions and the presence of starch-degrading enzymes.
Establishing phase and state diagrams of starch in terms of amylose +
amylopectin miscibility and complex formation would allow better control of
the self-assembly rate, and the size and crystallinity of spherulites. This
approach offers a route to tailoring the structure-related properties of starch,
such as solubility, thermal stability, and retention and release of small ligands
from starch matrices. One application could be the encapsulation of active
compounds into partly crystalline starch material via a solid liquid separation
process.
References
1. C. Martin and A.M. Smith, Plant Cell, 1995, 7, 971.
2. V.I. Kinseleva, N.K. Genkina, R. Tester, L.A. Wassermann, A.A. Popov
and V.P. Yurev, Carbohydr. Polym., 2004, 56, 157.
3. S. Fujimoto, T. Nagahama and M. Kanie, Die Sta ¨ rke, 1972, 24, 363.