Effect of gelatinisation on textural properties of complex starch gels: combining microscopy and water distribution to quantify gelatinisation degree

Summary

Numerous foods contain starch as thickener or gelling agent, providing specific textural properties that vary based on type of starch (botanical source and chemical modifications) and different processing parameters (amount of water, heating temperature and heating time). A specific amount of water is required to fully gelatinize the starch granules at temperatures that are starch type dependent. Other water-binding ingredients will affect the gelatinisation degree
of the starch, affecting the final structure of the system. The water distribution is therefore an important parameter that should be quantified in order to interpret the contribution of starch to the properties of the end product. In the present work, we studied the gelatinisation degree of two types of starch by observing the evolution of granule morphology by microscopy, that of size distribution by dynamic light scattering and by quantifying changes in the distribution of water (bound vs free) in time by centrifugation techniques. This made possible to estimate the gelatinisation degree of starch granules and the microstructure of starch gels. At low gelatinisation degree, the starch swelled a few times the original size and formed a compact particle gel, while at high gelatinisation degree, the starch granules totally collapsed, leaching amylose into the continuous aqueous phase and forming a polymer gel. The final gel type
influenced the properties of the starch gel. The characterization of textural properties showed that the particle gels in which the starch granules were still recognizable were quite hard and brittle, while gels of the polymer type were soft and elastic. The possibility of linking gelatinisation degree, microstructure and textural properties of starch gels allows us to study the role of this ingredient in the functional and sensory properties of more complex systems
and, ultimately, to modulate these properties for several types of foods.