Aqueous extraction of organic amaranth starch and their by-products

Abstract

The aim of this study was to characterise the organic amaranth flour (Amaranthus caudatus), native starch and by-products generated after its aqueous extraction (bagasse, post-sieving and post-centrifugation residues) and to evaluate the influence of lipids on the thermal, structural and pasting properties of these samples. The analyses performed were: thermogravimetry (TG), differential scanning calorimetry, viscographic analysis, scanning electron microscopy with field emission gun and Fourier-transform infrared spectroscopy (FTIR). After aqueous extraction, the amaranth starch presented low protein and lipid content, which were retained together with inorganic material mainly in the post-sieving and post-centrifugation residues. TG curves showed three mass losses, associated with dehydration, macronutrients decomposition and oxidation of organic matter. These losses were consecutive for flour, bagasse and residues, resulting in a stability period after degreasing, which increased for the sample of defatted starch. About gelatinisation, the presence of lipids, fibre or proteins hinders the starch gelatinisation and the increase of viscosity, requiring higher energy. By microscopy, it was possible to identify different characteristics according proximal composition in each studied fraction. Three regions were identified by FTIR (lipid, protein and carbohydrates), and the spectral bands corroborated with the proximal analysis. The results obtained encourage the aqueous extraction of starch from organic sources, as well as future studies to evaluate the use of the generated residues in food formulations or starch films. The lipids removal process becomes interesting for the amaranth starch, favouring the occurrence of the gelatinisation process, property of greater industrial interest.