Characterisation, in vitro digestibility and expected glycemic index of commercial starches as uncooked ingredients

When selecting a native starch for specific food purposes, it is important to consider the differences between starches of varying botanical sources (cereal, tubers and roots). In this study uncooked starches as ingredients (corn, rice, wheat, tapioca and potato) were characterized according to microstructure, some (physicochemical, functional and thermal) properties, in vitro digestibility and expected glycemic index. There was a significant variation in the granule shape and size distribution of the starches, when studied using Scanning Electron Microscopy (SEM) and particle size analysis. Particle size results distinguished among starches in monomodal (corn, tapioca, potato) and bimodal (rice, wheat) populations. Among all the samples, the potato showed the biggest size distribution granules while the rice showed the lowest. The examined properties and nutritional characteristics of starches were significantly different. Thermal properties were studied by means of Differential Scanning Calorimeter (DSC). DSC studies found that the transition temperatures (58.8 °C - 78.7 °C) and enthalpies of gelatinization (2.3 J/g - 8.2 J/g) of the starches appeared to be greatly influenced by microstructure and chemical composition (e.g. resistant starch). Potato and corn starches were hydrolyzed more slowly and to a lesser extent than ones. In particular, the highest resistant starch was recorded for potato. Nutritional properties such as slowly digestible starch and expected glycemic index values followed the order: rice > wheat > tapioca >corn > potato. In general, these results provide the baseline information on the development of novel foods or native starch blends with tailored functional properties such as slow digestibility.