Preparation of controllable porous starch with different starch concentrations by the single or dual freezing process

Porous starch (PS) was created by replacing ice crystals in frozen starch gel with ethanol using a solvent exchange technique. In the single freezing process, the porous structures of PSs were controlled by changing the starch paste concentrations. With the increasing of concentrations from 5 to 20%, pore size, moisture adsorption, oil adsorption capacity and methylene blue (MB) adsorption of PSs decreased greatly, while the apparent density increased from 0.093 to 0.689 g/cm3. In the dual freezing process, the porous structures of citric acid-modified PS (CAPS0) were full of starch pastes with different concentrations (1.5, 2.5 and 3.5%), and then frozen again. Compared to CAPS0, PSs from the dual freezing process exhibited larger apparent density and MB adsorption, but lower moisture adsorption and oil adsorption capacity. And the starch paste concentrations (1.5–3.5%) had few effects on the properties of PSs in the second freezing process.