Identification and Characterization of the Starch Granule-Associated Proteins of Cereal Starches after Alkali Treatment

Starch granule-associated proteins (SGAPs) of four cereal starches subjected to different alkali treatments were investigated. Starch synthesis-related proteins were identified as the major SGAPs in normal and waxy maize starches. In rice starch, seed storage proteins were the majority of SGAPs. A concentric ring pattern of the SGAPs distribution was found in normal maize starch and normal rice starch, related to the granule-bound starch synthases. SGAPs of waxy maize starch mainly occur in starch channels, identified as starch synthases and starch branching enzymes. Alkali treatment decreased SGAPs by facilitating protein solubility and degrading the protein structure. Hydrothermal treatment promoted the effect of the alkali. After alkali treatment, the proportion of starch synthesis-related proteins in total SGAPs significantly increased, indicating that these were more resistant to alkali, as they were tightly bound to starch granules. This study revealed the heterogeneity of SGAPs in starch granules and their response to the alkaline treatment.