Pretreatment of Corn Starch by Extrusion Combined with Soaking in Sulfite Acid

In order to solve the problems of long soaking time and low starch yield in traditional corn wet milling process, the feasibility of extrusion technology as pretreatment for corn to improve the starch extraction was carried out. The extraction rate and the purity of starch were studied by changing the extrusion temperature, extrusion moisture, screw speed, soaking time of H₂SO₃. After the single factor experiments, the response surface analysis (RSA) method which had four factors and three levels were used to determine the extraction technology of corn starch. The results showed that, the optimum process of corn starch extraction was that: The extrusion temperature was 40 ℃, extrusion moisture was 53%, the screw rotation speed was 194 r/min and the soaking time of H₂SO₃ was 14 h. The starch extraction rate reached to 93.25% in this method, which was 1.79% higher than that in traditional wet grinding process, and the production time was shortened by 34 h. Fourier transform infrared spectroscopy (FT-IR) showed that extruding pretreatment did not change the chemical structure of starch and the scanning electron microscope (SEM) images showed that, though slight wrinkles and depressions appeared on the surface of extruded starch granules, the shape of the particle remained intact. Therefore, it was confirmed that extrusion technology was effective to separate and extract the corn starch.