Dry method preparation of potato starch and its high value-added utilization

Dry preparation of potato starch is one of the most important procedures in food processing. Existing potato starch extraction can be limited to the low starch yield and a large amount of wastewater. This study aimed to develop the dry preparation of potato starch for high yield in sustainable agriculture. The processing steps were as follows: Potatoes were washed, peeled, cut into cubes, and then pressed to obtain potato press cake and juice. The press cake was subsequently treated by hammer crushing and sieved to separate potato starch from potato residue. It was found that the moisture content of the press cake was crucial for the dry separation of starch. Dry separation of starch was achieved at a moisture content of the press cake below 38.5%. Hammer crushing better maintained the intercellular connections between cell walls, thereby facilitating starch sieving. The performance was significantly superior to that of blade crushing. The starch yield of 17.8% was achieved with a moisture content of 13.6%, a starch content of 88.7% (dry basis), a protein content of 1.94%, and an ash content of 0.60% under optimal conditions. When the pressing pressure was insufficient (20 MPa), drying treatment was used to reduce the moisture content of the press cake. But the starch content and whiteness of the starch product decreased significantly. A comparison was made of the commercial products of potato starch. The starch content (wet basis) was between those of the two commercial products. But the starch content (dry basis) of 88.7% was lower than that of the commercial products (92.0% and 92.4%), while the whiteness was slightly lower as well. The starch after water extraction was further clarified using starch yield, crystalline structure, gelatinization properties, and damage rate. The results indicated that the starch yield was significantly higher than that of the water extraction (12.8%). Crystalline structure analysis showed that the crystal type of potato starch remained unchanged, with the B-type. In terms of gelatinization characteristics, the peak viscosity, trough viscosity, and breakdown of potato starch decreased significantly, whereas the final viscosity and setback increased, indicating suitability for conventional applications. The damaged starch content increased significantly, as the cracks on the surface of starch granules accounted for approximately 70% of the total. These cracks made the starch more susceptible to hydrolysis by α-amylase. The porous starch shared the better adsorption properties under optimal conditions (enzymatic hydrolysis for 12 h), with a water and oil absorption capacity of 156.6% and 101.9%, respectively. The scanning electron microscopy confirmed that there were some cracks on the surface of starch granules. The outstanding pores appeared after 12 h of enzymatic hydrolysis.