Emprego de técnicas termoanalíticas na análise de amidos nativos e quimicamente modificados de diferentes fontes botânicas

Abstract

Corn and cassava starches are used thoroughly in several industrial applications. Due to some intrinsic characteristics, chemical modifications in the structure of the starch granules have been developed. In this study, thermo-analytical techniques (TG/DTA and DSC), optical microscopy and X ray diffratometry were used in the analysis of acid-modified (0.15M HCl at temperatures of 30°C and 50 °C), oxidized with different hypochlorite concentrations (0.8; 2 e 5 g Cl/100 g starch) and native corn and cassava starches. The granules of native starches presented characteristic morphology. The morphology of the granules didn't show alteration after oxidative modification but they had alterations in the external morphology after acid treatment. Through the X ray diffraction, it was confirmed the typical crystallinity of cereals and tubers of the native corn and cassava starches, respectively. After modifications there were no differences in the crystallinity patterns. The corn starch enthalpy of gelatinization (ΔHgel) reduced after oxidative modification, the same didn't happen for cassava starch. In general, as larger the oxidation degree, larger the enthalpy of elatinization and more exothermic were the reactions of starch decomposition. The onset temperature (To), peak temperature (Tp) and the enthalpy of gelatinization (ΔHgel) reduced after acid modification for the starches of both botanical sources.