Extraction and Characterization of Starch from Cowpea (Vigna unguiculata (L.) Walp.)

The starch extraction process was optimized by response surface Box-Behnken analysis with cowpea seed as raw material. The morphology, structure and physicochemical properties were characterized. Five factors and three levels of response surface analysis were used to determine the optimal parameters of cowpea starch extraction process: 420 mL NaOH solution, soaking time 17 h, ethanol 74 mL, oscillating speed 167 r/min, oscillating time 70 min. Under these conditions, the theoretical extraction rate was 62.13%. The extracted cowpea starch ash content was 0.17%, protein content was 0.87%, lipid content was 0.25%, cellulose content was 1.59%, solubility was 0.73%, swelling degree was 1.85 g/g. Scanning electron microscope images showed that cowpea starch granules were spherical or ellipsoid, and most of the granules were distributed in the range of 9~13 μm. Fourier transform infrared spectroscopy and X-ray diffraction analysis showed that cowpea starch had strong crystal structure and relative crystallinity, and showed typical C-type crystalline starch morphology. Thermodynamic analysis showed that the initial gelatinization temperature (T_o) was 73.86 ℃, the peak temperature (T_p) was 80.59 ℃, and the end temperature (T_c) was 88.53 ℃. The results showed that cowpea starch had a tight spatial structure and strong anti-gelatinization properties, and would have a great development potential in the field of food texture improvers.