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 chemica l potential from the shell to the center in freshly panned jellybeans, was revealed by water activity measurements. Subsequent three-dimensional imagi ng by a nuclear magnetic resonance technique (single point ramped imaging T -1 enhanced, SPRITE), especially suited for detection of components with re stricted mobility as in low moisture foods, demonstrated the migration of m oisture from the shell to and through the center over a 48 h period followi ng engrossing. During this period, nuclear relaxation times were longer in the shell than in the center, where strong magnetic interactions with macro molecules are probably enhanced by proton exchange and hydrogen bonding. Wh ile some mass transfer occurs between the shell and the center, measurement s of total NMR image intensity suggest a net loss of moisture from the jell ybean to the atmosphere. This was verified by gravimetric measurements, whi ch also indicated that the process is diffusion-limited. It appears that at tempts to reduce the aging period between engrossing and polishing of jelly beans should be geared toward factors that increase the diffusion of moistu re. (C) 2001 Elsevier Science Ltd. All rights reserved.