Moisture migration in soft-panned confections during engrossing and aging as observed by magnetic resonance imaging

A driving force for moisture migration, namely, a gradient in water chemical potential from the shell to the center in freshly panned jellybeans, was revealed by water activity measurements. Subsequent three-dimensional imaging by a nuclear magnetic resonance technique (single point ramped imaging T-1 enhanced, SPRITE), especially suited for detection of components with restricted mobility as in low moisture foods, demonstrated the migration of moisture from the shell to and through the center over a 48 h period following engrossing. During this period, nuclear relaxation times were longer in the shell than in the center, where strong magnetic interactions with macromolecules are probably enhanced by proton exchange and hydrogen bonding. While some mass transfer occurs between the shell and the center, measurements of total NMR image intensity suggest a net loss of moisture from the jellybean to the atmosphere. This was verified by gravimetric measurements, which also indicated that the process is diffusion-limited. It appears that attempts to reduce the aging period between engrossing and polishing of jellybeans should be geared toward factors that increase the diffusion of moisture. (C) 2001 Elsevier Science Ltd. All rights reserved.