Long-term stability of waxy maize starch/xanthan gum mixtures prepared at a temperature within the gelatinization range

The retrogradation behavior of waxy maize starch pastes with added xanthan gum was investigated. The pastes were prepared with or without added xanthan gum at two starch concentrations (5:100 and 7:100), at two temperatures within the gelatinization range (70 °C or 72 °C) and at acid or neutral pH. The evolution of the macrostructure (texture, flow behavior and syneresis), microstructure (oscillation rheology) and molecular aggregation (pulsed-field NMR) of the pastes was followed up in an 8 week period during cold storage (7 °C). Heating temperature was found to have a profound effect on the long-term stability of the pastes. Pastes prepared at 70 °C behaved as flocculated dispersions of largely intact, swollen granules which resulted in stable structural properties during the preservation period. At 72 °C, a higher degree of gelatinization and degradation was observed, resulting in structurally unstable systems due to association and crystallization of amylopectin. Especially for these systems, xanthan gum was found to enhance the gelation process, probably due to phase separation. Although xanthan gum may restrict the granule disruption during preparation, this beneficial effect on the freshly prepared pastes did not result in an improved stability during storage.