CONICET | Buscador de Institutos y Recursos Humanos

Starch acetates and starch butyrates with degree of substitution (DS) in the range of 0.06?1.54 wereprepared by a simple direct solvent-free organocatalytic methodology of starch acylation. The starchesters synthesized have important applications in the food and pharmaceutical industries, among others.The acylation methodology used involves a non-toxic biobased -hydroxycarboxylic acid as catalyst, andproceeds with high efficiency in absence of solvents. The effect of reaction time on the advance of starchmodification was studied as a simple way to control the level of substitution achieved, when all otherreaction parameters were kept constant. Starch esters were characterized by means of Fourier transforminfrared spectroscopy (FTIR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA)and X-ray diffraction (XRD). FTIR spectroscopy qualitatively confirmed the esterification of starch by theappearance of bands which are associated with esters groups. Scanning electron microscopy showed thatthe granular structure of the polysaccharide was preserved upon acylation, although acylated granuleshad rougher surfaces; and wrinkles, grooves and deformed zones appeared in some granules at high DS.Thermogravimetric analysis showed a gradual reduction in the water content of acylated starches, aswell as noticeable changes in their thermal properties at increasing DS. X-ray diffraction analysis showedthat the acetylation treatment led to lower crystallinity at increasing DS, although characteristic cornstarch A-type patterns could be identified even at the highest DS achieved (DS = 1.23). Specific bands andweight losses derived from FTIR and TGA data could be very well correlated with the substitution degreeachieved in acetylated starches at DS lower/equal than 0.6. The organocatalytic methodology describedfor the synthesis of starch acetates and butyrates has the potential to be easily extended to the synthesisof other starch esters using a variety of anhydrides or carboxylic acids as acylating agents.