302 Starch/Stärke 51 (1999) Nr. 8-9, S. 302–307 © WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1999 0038-9056/99/0909-0302$17.50+.50/0 1 Introduction Polysaccharides and their derivatives are finding increas- ing industrial applications because of the broad range of functional properties they exhibit. Substantial efforts have been realized, e.g. at developing methods to esterify the hy- droxyl groups with fatty acids and their derivatives. The in- troduction of an ester group into polysaccharides constitutes an important synthetic task, because it permits to modify their original hydrophilic nature and to obtain enhanced or new thermal and mechanical properties. Mullen and Pacsu and Sagar et al. described the prepara- tion of starch esters by reacting starch with fatty acid chlo- rides in organic solvents such as pyridine or dimethylform- amide [1, 2]. Despite the high degree of substitution (DS) – defined as the number of substituents per anhydroglucose unit, three being the theoretical maximum – that these meth- ods allow, the utilization of an organic solvent is prohibited for industrial applications, especially in the food sector. In a previous study, we developed a method for esterify- ing potato starch with octanoyl chloride in the absence of an organic solvent, using a nitrogen stream to eliminate the hy- drochloric acid produced by the reaction [3]. The synthesis of the octanoated starch without solvent was possible by pre- vious esterification of the hydroxyl groups with formic acid at ambient temperature. The formylation gelatinizes potato starch and allows further esterification of free hydroxyl groups by octanoyl chloride. After optimization of main pa- rameters to obtain both a high DS and recuperation yield (RY), a DS value of 1.7 and a recuperation yield of 89% of the solid phase were obtained, respectively. In order to verify the influence of different starch sources on esterification of hydroxyl groups of starch, the synthesis was carried out at the optimal experimental conditions (105 °C/40 min) of the corresponding octanoated starchy material. Afterwards, higher fatty esters (C 8 to C 18 ) of potato starch were prepared in order to elucidate the influence of the fatty chain length on DS and yield values. Several au- thors have shown that the grafting of fatty chains onto starch improves the thermoplastic character and thermal stability of the resulting starch esters [1–4]. The presented study con- centrated on characterization and properties of the different fatty starch esters obtained: X-ray pattern, hydrophobic char- acter, thermal and mechanical properties. 2 Experimental 2.1 Materials French potato, maize, wheat, rice, Eurylon 7 and waxy starch were supplied by INRA (Nantes, France). Amylose and amylopectin from maize at the dispersed state as well as formic acid solution 99% (FA) were provided by SIGMA, France. Fatty acid chlorides (FAC) were purchased from ALDRICH, France. 2.2 Methods Elemental analysis was carried out on a Carlo Erba 1106 apparatus after drying the samples at 100 °C for 24 h. The IR spectra were recorded on a Perkin Elmer 1610 FTIR spectrometer, while the proton NMR spectra were recorded on a Bruker 200 MHz FT spectrometer. The chem- ical shifts were expressed in ppm either with respect to CDCl 3 or deuterated DMSO, depending on the solubility of the compound. Diameter and shape factor determination of granules of different starch sources were performed using a OLYMPUS PMG 3 optic microscope followed by image analysis with the software CUE-2 IMAGE ANALYZER. To dye the starch granules or particles, 20 mg (dry matter) of starch were added to 5 mL of distilled water following by a droplet of an 1 N iodine solution. 2.2.1 Synthesis of fatty starch esters A sample of 2.5 g native starch, dried for 2 h at 105 °C to obtain a moisture content of less than 2%, was placed with formic acid (4.3 eq/eq glucose) in a three-necked flask equipped with a mechanical stirrer, a Dean-Stark trap, a tube for introducing reactants via a peristaltic pump, and a tube for introduction of nitrogen. A flask containing 60 mL of 2 N sodium hydroxide solution with a cooling system was placed in the outlet. The formylation reaction was carried out by im- pregnating the corresponding starch with formic acid at A solvent-free synthesis and the properties of esters of starch from dif- ferent sources (maize, waxy maize, Eurylon 7, potato, wheat, rice, amy- lose, and amylopectin) and higher fatty acids are described. Higher fat- ty acid esters (C 8 -C 18 ) of potato starch were synthesized by chemical gelatinization using formic acid, followed by treatment with fatty acid chlorides. Esterification was readily carried out at 105 °C and a reaction time of 40 min. Formic acid permits esterification of starch by long- chain acid chlorides with minimum degradation. The results indicated that the degree of substitution of the starch esters diminishes with in- crease in fatty acid chain length. All starch esters have a hydrophobic character which rises with length of the fatty side chain. X-ray and Dif- ferential Scanning Calorimetry (DSC) showed that the fatty acid side chains (C n > 16) grafted onto starch form cristallites between them. This phenomenon provokes the decrease of elongation at break for these starch esters. On the other hand, the tensile strength at break and ther- mal stability of fatty esters of starch increase both with a higher fatty chain grafted onto starch. Free-solvent Synthesis and Properties of Higher Fatty Esters of Starch – Part 2 Jorge Aburto, Hassina Hamaili, Geneviève Mouysset-Baziard, François Senocq, Isabelle Alric, and Elisabeth Borredon, Toulouse (France)