Starch Crystallinity and Microstructure of Thermo-Mechanical Modified Quinoa Flours

The aim was to analyze, based on a Doehlert design, the effect of rotional speed (250–450 rpm) and milling time (10–50 min) on starch crystallinity (X-ray diffraction) and microstructure (SEM) of quinoa flours modified by planetary ball-milling. Milling protocol with balls:seeds of 5:1 involved cycles of grinding (10 min) and pause (40 min). XRD Type A crystallinity patterns with diffraction peaks at 15, 17, 18 and 23° were found. The amorphous (non-crystalline) starch increased as milling progressed. In comparison with control (flour obtained in a blade mill), crystallinity was reduced between 9% and 15% within 250–450 rpm for 20 and 40 min respectively. SEM images of modified flours showed lower size particles with rounded edges and polished surface in comparison with sharp edges particles of control. At 2500× magnification, polyhedral starch particles (1–3 μm) were observed immersed in a continuous matrix composed of hemispherical sub-micrometric starch particles. Both starch particles, because of their different size and shape, influence the physicochemical properties of quinoa flour. The results showed that high-impact milling is particularly suitable for producing structural changes in starch. Such starch modifications can be expected to have an impact on the functional behavior of flour during food development.