Starch, in particular the linear amylose, is able to form inclusion complexes with a wide spectrum of ligand molecules, among them flavor compounds. The complexing ability of a homologous series of gamma- and delta-lactones with potato starch was followed by amperometric iodine titration, differential scanning calorimetry, and wide-angle X-ray diffraction measurements. Lactones with a linear chain of a size > or = C(5) form inclusion complexes with starch, whereas lactones with a short linear chain, such as gamma-heptalactone, show poor complexing ability. The thermal stability of starch-lactone complexes increases with increasing chain length of the lactone. In general, lactones induce the formation of V(h) helices. Only delta-decalactone complexes with starch were not definitely identified as V(h) amylose helices. Complexation of starch dispersions with lactones induce turbidity and gelation or phase separation, both phenomena being the result of microphase separation.