Physicochemical and structural changes of cassava starch modified by pyrodextrinization with glacial acetic acid as catalyst

Abstract

This article aimed to produce pyrodextrins from cassava starch (Manihot esculenta C.) using glacial acetic acid (CH₃COOH) and to analyze the effects of the modification on the physicochemical and structural properties. The central composite rotational design (CCRD) was carried out, using an α = ± 1.68 to generate 19 total trials (8 factorial points, 6 axial points, and 5 repetitions in the central point) to evaluate the effects of acid concentration (0.58–6.70 g acid/kg starch on a dry basis), temperature (100–200 °C) and incubation time (29–331 min) on pyrodextrins. Pyroconversion was carried out by spraying the acid solution on the starch powder. The response variables were available starch (AS) content and color difference (ΔE) index. Morphological, structural, thermal, rheological, and physical characterization analyses were then carried out. Pyroconversion reduced (P < 0.05) the AS content between 4.4ー42.2 % with minor changes in the ΔE index, except for Pyrodextrin-12, prepared with 3.64 g/kg heated at 200 °C for 180 min, the least digestible and darkest pyrodextrin. Pyrodextrins 8 and 12 were cream-yellow colored, water-soluble and low viscous materials. IR and NMR spectra of pyrodextrins showed a reduction in the presence of the α(1,4) glycosidic bond typical of starch, indicating a change in its chemical structure. CH₃COOH proved to be an efficient acid for reducing the in vitro digestibility of cassava starch by pyroconversion, without drastically changing the color of pyrodextrin.