The effect of slight milling on nutritional composition and morphology of quinoa (Chenopodium) grain

Abstract

This study conducted a detailed evaluation of the nutritional value and proximate composition of milled quinoa grain at different dehulling rates with the goal of identifying a range of dehulling rates that retain the maximum level of nutrients and phytochemicals.Eleven samples of quinoa grain processed at different dehulling rates were obtained through light abrasive milling. The relationship between the dehulling rate and the nutritional composition of quinoa grain was determined. As the dehulling rate increased, the proportions of protein, fat, dietary fiber and ash decreased, whereas the proportion of starch increased. With the increase of dehulling rate, increasing amounts of protein, fat, starch, dietary fiber, saponin, flavonoids, and total phenolic were lost with the hull residue. At the dehulling rates of 8.6%, 11.72% protein, 7.57% fat, 4.72% starch, 28.9% total dietary fiber, 45.5% soluble dietary fiber, 48.58% saponin, 26.18% flavonoid, and 42.25% total phenolic were lost in dehulled quinoa grain compared with the raw quinoa grain. Optical microscope photos and scanning electron microscope (SEM) images showed that only the pericarp of quinoa was scoured when the dehulling rate was below 8.6%, and the quinoa grain retained a complete embryo. Therefore, to retain maximum nutritional and phytochemical content in the quinoa and maintain quinoa grain integrity, it is necessary to limit the dehulling rate of quinoa in the range of less than 8.6%.