Quinoa starch nanocrystals production by acid hydrolysis: Kinetics and properties.

Quinoa starch (QS) acid hydrolysis was investigated, focusing on the kinetics and physicochemical properties of nanocrystals production as a function of temperature (30, 35 and 40 °C). Waxy maize starch (WMS) was hydrolyzed at 40 °C for comparison. QS presented different hydrolysis percentages at 30 °C (63%), 35 °C (73%) and 40 °C (91%), on the fifth day. QS showed faster hydrolysis (first-order rate constant, k = 0.59 day-1) than WMS (k = 0.39 day-1) at 40 °C. Material produced at 30 °C was micrometric-sized and irregularly-shaped while that at 35 and 40 °C, was nanometric-sized and conical and parallelepiped-shaped. The hydrolysis temperature increase did not affect the crystallinity index of quinoa starch nanocrystals (QSNC), whereas zeta potential and Fourier transform infrared spectroscopy band intensities increased, and thermal transition peak temperature and thermal stability decreased when hydrolysis temperature increased. QSNC were produced at 35 and 40 °C with yields of 22.8% and 6.8%, respectively. At 40 °C, QSNC presented smaller sizes than WMS nanocrystals, but also lower yield and crystallinity index.