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Retrogradation of Starches from Different Botanical Sources¹

Retrogradation in 2% pastes prepared from unmodified commercial starches by cooking at 98–100°C under low shear, then held at 4°C for 56 days, was examined by turbidometric analysis and light microscopy. Turbidometric analysis revealed that retrogradation rates followed the order of wheat, common corn > rice, tapioca, potato >> waxy maize. Microstructures of stored pastes were examined both before and after centrifugation. Granule remnant morphologies and fresh and stored paste microstructures were unique to each starch examined. Fresh pastes from amylose-containing starches were dominated by networked amylose that condensed into higher density aggregates upon storage. Unique phenomena seen in some stored pastes included interactions of granular remnants with aggregated amylose, composite networks of co-associated amylopectin and amylose, and slight birefringence regained by granule remnants. Microstructural changes in stored pastes could be related to changes in turbidity and to the results of other methods used to quantitate retrogradation.