The purpose of this study was to understand the effect of relative humidity (RH) on amylose-lipid complex (ALC) formation in amylose-lauric acid blend powder held at 50 ºC (temperature slightly higher than the melting point of lauric acid) using differential scanning calorimetry (DSC) and X-ray diffraction. From DSC curves, the melting of crystalized lauric acid and two melting peaks of ALC were observed depending on RH.ALC formation was confirmed by X-ray diffraction pattern. The melting enthalpy (ΔHm) of lauric acid in the sample held at RH 0% was lower than that of lauric acid only though there was no ALC formation. This suggests that crystallization of lauric acid was prevented by amylose. The ∆Hm of lauric acid increased with an increase in RH up to 79.0% because liquid lauric acid would have fused as the result of enhanced repulsive force between liquid lauric acid and hydrated amylose. The ΔHm of ALC increased with an increase in RH between 79.0% and 95.0%. For ALC formation, amylose has to be mobile in the system, but dehydrated amylose is in a glassy (immobilize) state. According to the glass to rubber transition behavior of amorphous polymer, amylose held at 50 ºC is suggested to become rubbery (mobile) state at RH 76.0%. This interpretation will explain the reason why ALC formation began to be observed at the RH range between 72.4% and 3 79.0%.

No abstract