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

Abstract

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.