Effect of Starch Isolation Method on Structural and Physicochemical Properties of Acorn Kernel Starch

Starch is isolated from kernel of acorn fruit (Quercus fabri) using different methods, including hot-water soaking (HWS), alkaline washing (ALW), ultrasonic-assisted ethanol soaking (UAES), and ultrasonic-assisted hot-water soaking (UAWS). Structural and physicochemical properties of starches isolated using these methods are investigated. The surface structure of acorn starch granules varies depending on the isolation method. However, a similar C-type crystalline pattern is found for all the isolated starch samples. Acorn starches isolated using the ALW and UAES methods exhibit a greater degrees of crystallinity than those of starches isolated using the other methods. FT-IR spectra analysis reveals that the chemical bonds in starch molecules are not affected during the isolation of acorn starch under different conditions. Moreover, starch isolated using the UAES method exhibits the greatest water solubility, swelling power, and light transmittance values, as well as the lowest tannin content. In addition, the lightest white color is found for starch isolated using the ALW method. Furthermore, the HWS and ALW methods result in acorn starch with greater enthalpy and gelatinization temperatures, whereas the UAES and UAWS isolation methods result in acorn starch with greater peak viscosity. The obtained results provide important knowledge about the differences in physicochemical properties of acorn starch isolated using different methods.