Pulsed NMR measurements of freeze/thaw-induced retrogradation of corn and wheat starch gels: Correlation with rheological measurements

The suitability of using pulsed-nuclear magnetic resonance (pulsed NMR) as a convenient method to evaluate the freeze/thaw stability of starch gels has been investigated. The changes in the NMR “solid-like” component (reflective of freeze/thaw-induced retrogradation) were correlated with concomitant changes in uniaxial compression properties of maize and wheat starch gels after freeze/thaw cycling. The content of “solid-like” component of the starch gels increased non-linearly as the number of freeze/thaw cycles increased, a pattern which is indicative of starch retrogradation induced by freezing/thawing. Maximum force (reflective of the hardness or strength of the gel) was found to have the best correlation with % solids as determined by the pulsed NMR method, followed by modulus and fracturability. Correlations between pulsed NMR readings and rheological measurements would not be expected to be very good, unless such correlations were made using data only up to the point when structural disruption occurred.