Alkali-Induced Changes in Functional Properties and in Vitro Digestibility of Wheat Starch: The Role of Surface Proteins and Lipids

The bread wheat starch was treated with 0.025 and 0.0625 M NaOH solution for 1, 2, and 3 weeks at 30 °C, and the changes in functionality and in vitro digestibility were evaluated. NaOH treatment reduced protein and lipid contents of wheat starch from 0.46 to 0.20% and from 0.59 to 0.25%, respectively. No significant changes were observed in the amylose content, relative crystallinity, and short-range order of double helices, but there was evidence showing that morphology of some starch granules was altered. The swelling power and starch solubility of wheat starch increased from 11.4 to 14.1 g/g and from 10.9 to 22.1%, respectively. The thermal transition temperatures were increased greatly, but the enthalpy change remained largely unchanged. Alkali treatment greatly decreased the pasting temperature, but the pasting viscosities were altered in different ways. The resistant starch (RS) content of wheat starch was decreased significantly from 69.9 to 45.2%, while the starch that is digested slowly (SDS) content was increased greatly from 13.6 to 34.5%. Our results showed that alkali treatment can significantly alter the functionality and in vitro digestibility of wheat starch granules by removing the surface proteins and lipids rather than significantly altering the internal structure of starch granules.