2001 AACC Annual Meeting Charlotte, North Carolina October 14-18, 2001 Charlotte Convention Center

Recently, Hills and co-workers (2000) used proton NMR relaxometry to study the mobility of water in native starch granules from a range of botanical sources and were able to extract from the continuous spin-spin relaxation spectrum of water information regarding both the granule structure and the polymorphism of the amylopectin crystallites. This advanced interpretation of the relaxation data on starch granules is not unequivocal due to the complexity of the system where several issues can interfere with T(2) values (granule size and composition, degree of crystallinity, polymorphism). This study concentrates on the effect of polymorphism on the mobility of water. In order to exclude the interference of the aspects listed above, waxy maize starch was used and the A and B polymorphs were obtained by allowing amylopectin recrystallisation in an extruded system (constant water content) at different temperatures. The relaxation spectrum obtained by fitting the CPMG decay to a continuous distribution of T(2)s of the freshly extruded (amorphous), retrograded at 45 C (A-polymorph) and retrograded 4 C (B-polymorph) were compared. The effect of the extent of hydration on the water mobility spectrum was assessed by studying samples of the A and B polymorphs stored over a range of relative humidity. The results showed a single T(2) distribution for both forms. This observation is in contradiction with the findings of Hills and co-workers who claimed to be able to identify the intra-crystalline water in starches of the B-type. Unexpectedly, a higher degree of mobility of water was consistently found in the B polymorph.