A calorimetric study of the interaction between waxy maize starch and lipid

There is considerable debate on the definition and measurement of the amount of amylose in starch and whether hydrophobic ligands can form a complex with amylopectin. One method for amylose determination is through the measurement of amylose-lipid complexation using differential scanning calorimetry (DSC), with the assumption that amylopectin cannot form such a complex. As the sensitivity and methodologies used for DSC improves, the validity of this assumption needs to be tested once again. For the experimental work, alpha-L-lysophosphatidylcholine (LPC, 10% of starch dry weight) was used as the complexing agent and waxy maize starch. Optimisation of the DSC included changing the heating rate from 10 degrees C/min to 40 degrees C/min, which resulted in a higher sensitivity enabling the recording of an endotherm associated with the dissociation of a starch-LPC complex. The observation of the endothermic formation of such complex could only be achieved when a microcalorimeter, which analyses a much larger sample than a standard calorimeter (190 mg of dry starch compared to 13 mg) was used. There are two possible interpretations for these observations: Either waxy maize starch contains traces of amylose (similar to 0.5-0.7%) and the DSC is sufficiently sensitive to detect these amounts or the alpha-1,6 glucan long branches of waxy maize starch bind linear aliphatic compounds.