Amido de capim-arroz (Echinochloa crusgalli (L) Beauv.): caracterização e modificação por acetilação e tratamento térmico em baixa umidade de forma isolada e associada

Abstract

The barnyard grass is a weed difficult to control found in abundance as part of the waste industry paddy. One way to add value to this waste would be the extraction of starch. The modification of starches aims to expand the range of use. The objective of this work was to extract and modify starch barnyardgrass and evaluate the effects of modification by acetylation under iodine catalysis and HMT in isolation and associated, on the level of substitution of acetyl groups, granular structure and functional properties. Acetylation was performed at 100 ° C during 10 min varying the amount of iodine as catalyst (1, 5 and 10 mM). The HMT was performed in starch conditioned to 25% moisture and autoclaved at 110 ° C for 1h. To conduct the combined modifications, starches have been modified by acetylation prior to HMT and vice versa. The degree of substitution (DS), infrared pattern, morphology and birefringence, polymorphic pattern, relative crystallinity, swelling power, amylose leaching, properties of viscosity and thermal properties of native and associed modified starches. The GS increases with the increasing addition of iodine used as catalyst. The HMT reduces the degree of insertion of acetyl groups to the starch. The changes affect the granular structure of starch barnyardgrass, from the formation of aggregates and dark spots in the center of some granules and reducing relative crystallinity, especially in modified starches so associated. The swelling power and amylose leaching increases after acetylation held in isolation and before the HMT, but decreases in starch modified by HMT and isolated prior to acetylation. Pasting properties are altered after the modification and a behavior dependent upon the level of addition of iodine is observed. The paste temperature reduces after acetylation and acetylation followed by HMT, but increases after HMT and HMT followed by acetylation. Acetylation under 1 and 5 mM iodine, and acetylation with 1 mM iodine followed by HMT cause increases in viscosity, but after acetylation in 10 mM followed by acetylation of HMT and at 5 and 10 mM iodine, reduction of viscosity is observed. After HMT and HMT followed by acetylation, all viscosities are reduced, such reduction being more expressive with increasing amount of iodine used. The acetylation reduces the gelatinization temperatures, whereas HMT and combined treatments cause increases therein. Reduction in enthalpy and broadening the range of gelatinization is obtained after all modifications.