Amylose-fatty acid inclusion complexes as examined by interfacial tension measurements

Amylose forms complexes with fatty acids under certain conditions, these complexes affect the functional properties of foods and could be potentially used as delivery systems of essential fatty acids in the human organism. This work uses dynamic and equilibrium interfacial tension measurements in order to investigate these complexes. First, the interfacial tension at the water/air interface under the conditions of complex formation (KOH 0.1N, pH=12.7) was measured for three fatty acids (capric, myristic and oleic) at different concentrations. Then, amylose-fatty acid complexes were formed at three different fatty acid to amylose ratios covering a range above and below the saturation concentration of the amylose helix. For all examined systems the dynamic interfacial tension of the mixed amylose-fatty acid solution was significantly higher than this of the fatty acid solution, showing that some of the fatty acid was no longer available to adsorb at the interface and suggesting its inclusion in the complex. Besides, the dynamic interfacial tension of the mixed system was lower compared to the pure amylose solution indicating that some of the fatty acid did not participate in the complexes even at fatty acid/amylose ratios well below the saturation concentration of amylose. Using the isotherm of the three fatty acids it was shown that the fatty acid excess depended on fatty acid-to-amylose ratio.