Diffusion of sucrose in osmo-dehydrofrozen apple

Abstract

Apple parallelepipeds were dewatered by osmosis in sucrose solution at 30°C for 3 h, and at 70°C for 1 h. Dewatered material was air-frozen at-12,-20, and-35°C and stored for 1, 3, and 6 months. After a prescribed time of storage, cryoscopic temperature, amount of non-frozen water, and effective diffusion coefficients were calculated based on sucrose concentration profiles in the frozen material. In frozen, osmotically dewatered apple, mass transfer was very slow. After 6 months of storage, large concentration gradients still occurred in the frozen material. Effective diffusion coefficients, based on sucrose concentration expressed as percent of the total mass of the sample, were statistically not dependent on storage temperature. They were dependent on sucrose concentration and varied from 2.10-14 m2/s, at high sucrose concentration, to 5.10-11 m2/s, at low sucrose concentration. On the other hand, effective diffusion coefficients, based on the sucrose concentration in non-frozen water, were dependent on storage temperature and sucrose concentration as well. They were from 1.10-15 m2/s to 2.10-12 m2/s.