Amaranth Milling Strategies and Fraction Characterization by FT-IR

Abstract

Amaranth nutritional value has been widely recognized, but the required conditions for its processing cannot be adapted to traditional technologies. For the proposal of alternative strategies, the changes of several components should be understood. Enriched starch and lipid-protein fractions of amaranth flour upon different milling treatments were obtained and characterized by attenuated total reflectance-Fourier transform-infrared spectroscopy. Starch- and lipid-protein-enriched amaranth fractions were obtained by abrasive milling; amaranth starch was isolated by wet-milling procedure, and flour samples were obtained from planetary ball milling. Changes on starch, protein, and lipids relative contents, on starch crystallinity and on lipids and protein stability after milling and 6-month storage, were evaluated. The Fourier transform-infrared (FT-IR) spectroscopy peaks of the main grain components were identified in the middle-infrared range. By calculating the ratios between height intensities of selected specific peaks, several characteristics of the samples could be explained: increased protein content and lipid proportion of the enriched fraction; decrease of the starch crystallinity degree by abrasive milling and especially by ball milling due to starch amorphization during these processes; and lipids modification in milled and in 6-month aged samples. FT-IR analysis can be considered a rapid, nondestructive, solvent-free, sensitive, and useful tool to investigate starch, lipid, and protein modifications provoked by processing and storage as well as to determine, based on intensity ratio, the relative proportion of grain components within amaranth milling fractions. The abrasive milling associated to planetary ball milling to obtain modified different fractions is presented as an interesting strategy for the processing of amaranth grain.