Structural, functional, and chemical properties of small starch granules: Andean quinoa and kiwicha

White, red, and black quinoa (Chenopodium quinoa W.) and kiwicha (Amaranthus caudatus) are increasingly consumed as specialty foods worldwide. Starch was extracted from these Andean grains and characterized by scanning electron microscopy, Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry, and enzymatic hydrolysis. All starches showed a similar shape and small mean diameter (2–4 μm) because their physicochemical, functional, and digestibility characteristics are related to specific intrinsic factors. Kiwicha starches had greater swelling power and solubility at different temperatures than quinoa starches. Kiwicha starch showed a lower final viscosity (approximately 550 mPa s) than quinoa starches (approximately 935.0–1015.0 mPa s), reflecting marked differences in molecular organization. The quinoa starches exhibited higher FTIR 1047/1022 ratios, indicating enhanced ordered crystallinity. The amylopectin molecular weight was similar for all starches (1.95–2.37 × 10⁸ g/mol). In contrast, significant differences in the molecular weight of amylose were exhibited for quinoa starches (1.01–1.11 × 10⁸ g/mol) and kiwicha starch (1.31 × 10⁸ g/mol). The in vitro enzymatic digestibility was similar for all starches, with marked fast and slow hydrolysis phases. The in vitro starch digestibility was determined by the size of the starch granules rather than by their structure.