Visualizing surface active hydrocolloids by atomic force microscopy

Gum arabic from Acacia senegal and water-soluble soybean polysaccharide extracted from soybean cotyledons have been visualized using atomic force microscopy (AFM). The images of gum arabic have revealed predominantly linear structures that are considered to represent the arabinogalactan fraction constituting the major fraction in the gum. In contrast, soybean polysaccharide appears as highly branched structures with linear branches of ca. 20-80 nm in length. This observation is consistent with the previously proposed structural model hypothesizing the presence of long neutral sugar side-chains bound to the backbone of rhamnogalacturonan. AFM has provided the first direct evidence for the difference in branching structures in these hydrocolloids widely utilized in the food industry as effective emulsifiers and stabilizers in oil-in-water emulsions.