Resumo

GUERRA-DELLAVALLE, D. et al. Effect of reaction time on the acetylation of plantain starch. Rev. Mex. Ing. Quím [online]. 2008, vol.7, n.3, pp.283-291. ISSN 1665-2738.

Plantain starch was acetylated at different times; the degree of substitution, reaction rate constant, morphology, X-ray diffraction pattern and thermal characteristics were evaluated. The degree of substitution (DS) rose with the reaction time and consequently the reaction efficiency increased. The reaction rate constant was higher in plantain (0.67 h^-1) starch than in maize starch (0.23 h^-1). Fourier transform infrared spectroscopy confirmed the introduction of acetyl groups in the starch molecule and the signal characteristic of this group (1226 cm^-1) was higher at longer reaction times. The starch granule surface, observed by scanning electron microscopy, showed more changes when the reaction time increased and those were minimal in plantain starch. This pattern agreed with the higher crystallinity peaks measured by X-ray diffraction in plantain starch and an amorphous pattern obtained in acetylated maize starch. Peak temperature (74.8 °C for native plantain starch and 71 °C for its acetylated counterpart) and enthalpy of gelatinization (12.89 J/g for native plantain starch and 7.44 J/g for its acetylated counterpart) decreased in the acetylated starches and the effect was higher at longer reaction times. It is possible to determine a reaction time in order to obtain an acetylated plantain starch with specific DS and physicochemical and functional properties.

Palavras-chave : chemical modification; plantain starch; acetylation; FTIR; SEM; WAXS; DSC.