Phase transition and swelling behaviour of different starch granules over a wide range of water content

The relationship between swelling behaviour and thermal transitions of starch was investigated by differential scanning calorimetry (DSC) in combination with swelling power of starch. Sodium dodecyl sulphate (SDS)-treated wheat, waxy maize and potato starches showed increasing swelling power with increasing water/starch ratio. In contrast, swelling power of untreated wheat and high-amylose maize starches increased initially with increasing water/starch ratio, and then remained essentially unchanged above a certain ratio. The main endotherm G of native and SDS-treated wheat starch broadened progressively with increasing water/starch ratio up to 10:1. SDS-treated wheat, waxy maize and potato starches showed a typical endotherm over the whole range of water/starch ratios from 0.33:1 to 25:1, but the maximum enthalpy change occurred at different water/starch ratios. Our results indicate that thermal transition behaviour of starch granules is a very complex process, which involves swelling and leaching of starch polymer molecules rather than the dissociation of double helices or melting of crystallites.