Rheological and thermal properties of aged starch pastes from three waxy maize genotypes

The theological and thermal properties of aged starch gels (15:85 starch-water) from three waxy maize genotypes (wx, wx shl, and du wx) during storage (4 degrees C for up to 25 days) were studied. After storage, changes of storage modulus (G') and phase angle (delta) of the gels as a function of temperature were measured using oscillatory rheometry. For the du wx samples, G' at 25 degrees C increased rapidly during the first four days of storage at 4 degrees C, compared to the gradual increases over the 25-day storage period for the wx and wx shl samples. A peak in G' at 45 degrees C was observed during heating for the du wx samples after 10 days of storage and for the wx sample stored for 25 days. The G' peak may have been due to syneresis in the gels. Retrogradation of amylopectin of the aged starch samples was examined using differential scanning calorimetry. The du wx starch had greater retrogradation enthalpies than the other two samples (which showed similar retrogradation behavior) throughout the storage. The retrogradation enthalpy of the du wx samples increased rapidly during the first seven days, followed by a slower increase through the rest of storage. For the wx and wx shl samples, no endotherm was observed during the first four days of storage, after which the enthalpy increased steadily as a function of storage time. Addition of sucrose delayed the formation of gel networks for all three starches. The greater tendency for gelling and retrogradation of the du wx starch might be attributed to the greater proportion of DP20-30 chains of the amylopectin.