John H. Salch

Steam jet cooking of high-amylose starch-fatty acid mixtures. An investigation of complex formation

We have investigated the formation of helical inclusion complexes when aqueous mixtures of high-amylose starch and lauric, myristic, palmitic and stearic acids are processed by steam jet cooking at 140°C. The amount of free fatty acid that complexes with amylose was compared with the amount complexed when the fatty acid was present in its water-dispersible, sodium salt form. Air-dried and finely-ground products prepared from lauric and myristic acids and their sodium salts were extracted to remove uncomplexed fatty acid. A quantitative Fourier transfrom infrared spectroscopic (FTIR) method, based upon absorption of the carboxylic acid carbonyl, was then developed to determine the amount of complexed fatty acid remaining in the product. For both of these fatty acid systems, only small differences in complex formation were observed between the free acid and the sodium salt. Although water solubility of these fatty acids is negligible at room temperature, solubility is apparently sufficient for complex formation under the high-temperature, high-shear conditions of the steam jet cooking process. Products prepared from lauric, myristic, palmitic and stearic acids and their respective sodium salts were also examined by X-ray diffraction. This technique confirmed the results obtained by FTIR and also showed that differences between free acid and sodium salt become more pronounced as the fatty acid increases in molecular weight, and water solubility is reduced. For the stearic acid system, complexation of free acid was roughly half that observed with the sodium salt.

Graft polymerization of methyl acrylate onto granular starch : Comparison of the Fe+2/H2O2 and ceric initiating systems

Graft polymerizations of methyl acrylate (MA) onto granular cornstarch were carried out in water with both ferrous ammonium sulfate/hydrogen peroxide (FAS/H 2 O 2 ) and ceric ammonium nitrate (CAN) initiation. Starch concentrations were 10, 20, and 30% in water, and the amount of MA used was either 0.5, 1, or 2 mol per AGU of starch. Two concentrations of FAS/H 2 O 2 were used : 1 mol each of FAS and H 2 O 2 per 100 AGU of starch, and 1 mol per 1000 AGU. Significant amounts of acetone-extractable PMA homopolymer were produced, and homopolymer formation was especially high at the 1 : 100 ratio. Sharp exotherms were observed, and reaction mixtures reached maximum temperature within 2 min or less. Total conversions of MA to PMA were higher at the 1 : 100 ratio, and conversions in some polymerizations were nearly quantitative. CAN-initiated polymerizations were run under the same conditions used for FAS/H 2 O 2 ; however, the amount of CAN used was limited to 1 mol per 100 AGU because of low conversions at the 1 : 1000 ratio. Compared with FAS/H 2 O 2 , CAN gave more moderate exotherms ; and longer time periods were required for reaction mixtures to reach maximum temperature. CAN gave quantitative conversions of MA to PMA, but only low percentages of PMA homopolymer were observed. Differences between FAS/H 2 O 2 and CAN initiation are consistent with differences in the two initiation mechanisms. High levels of homopolymer produced on starch granule surfaces with FAS/H 2 O 2 could be seen in scanning electron micrographs and were also apparent in infrared spectra obtained with an attenuated total reflectance (ATR) cell. ATR spectra of acetone-extracted products indicated that the amount of PMA actually grafted to starch granule surfaces was similar with both initiating systems. Tensile properties of extruded ribbons prepared from these polymers did not vary greatly with the initiator used.