Potential sources of error in the calorimetric evaluation of amylose content of starches

The l-α-lysophosphatidylcholine calorimetric method for determining amylose content of starches was used to characterize an amylose fraction derived from common maize starch using an aqueous leaching process. The enthalpy of amylose-LPC complexation and dissolution was significantly greater for the leached maize starch fraction compared with that for potato amylose, leading to erroneously high values for amylose content when potato amylose was used as the reference standard. This was not likely caused by a difference in molecular weight as previously proposed, but possibly to differences in degree of branching. A spherulitic morphology was observed after rapid cooling from 180 °C at low LPC concentrations, but its formation was inhibited at concentrations of lipid typically used in the LPC test. The mechanism of spherulite formation during rapid cooling in the absence of lipid appears to be different than that observed on slow cooling in the presence of lipid.