Organic solvent-free transesterification of various starches with lauric acid methyl ester a and triacyl glycerides

This study deals with the organic solvent-free synthesis of fatty acid esters of high-amylose maize (amylomaize) starch by transesterification with lauric acid methyl ester using potassium laurate as catalyst. The process involves thermal pretreatment of amylomaize in order to swell the polysaccharide and increase its accessibility and reaction with the esterification reagent. The swelling degree (Q) was monitored by UV-Vis spectrophotometry and scanning electron microscopy (SEM), whilst the formation of a complex between amylose and potassium laurate was confirmed by X-ray diffraction and FTIR studies. The transesterification reaction was carried out at 190 degrees C and a central composite design was used to obtain the corresponding contour plots with a second order model (gamma = beta(0) + beta(1)X(1) + beta(2)X(2) + beta(12)X(1) X-2 + beta(11) X-1 X-1 + beta(22) X2X2) and a confidence interval of 95%. The experimental design consisted of two independent variables, reaction time (2-6 h) and catalyst (2.2 - 33.8 meq catalyst per eq. glucose), and two dependent variables, the degree of substitution (DS) and the yield of the amylomaize starch ester (Y,%). Maximum transesterification of amylomaize starch (DS = 0.61) was obtained after 4:30 h at 190 degrees C with an intermediate concentration of catalyst (18 meq per eq. glucose). Finally, the optimized results were extended to other starch sources and vegetable oils.