Investigation of starch retrogradation using atomic force microscopy

The formation of molecular networks by retrogradation of gelatinised starch was investigated using atomic force microscopy in tapping mode. Specimens were prepared from wheat and maize starches that were mixed into a paste in a Rapid Visco Analyzer at 90 °C. The paste was subsequently diluted for specimen preparation. When diluted pastes from wheat starch containing 25.5% amylose and maize starch with 30.7% amylose were deposited on to a mica stage at 90 °C, an extended network structure was clearly evident. However, when monopalmitin, which forms complexes with amylose, was mixed in with the starch paste, aggregated structures were observed rather than a network. Aggregated structures were also observed in starch from waxy maize with specimens prepared at 90 °C. These results will be discussed in relation to the significance of amylose in the formation of starch gels after retrogradation.