Ionic diffusion in frozen starch gels.

Abstract

Quality changes in food frozen by different conditions and at different storage temperatures were demonstrated using a model system. A frozen starch gel represents a frozen food matrix, and ions in the external medium represent the reactant molecules. We determined the effective diffusion rates of Zn+2 ions into frozen starch gel cylinders that were frozen at different freezing rates. The diffusion was performed at -8 degrees and -15 degrees C. The amounts of ion diffused were determined by atomic absorption, whilst the structure of the frozen samples could be simultaneously determined by scanning electron microscopy. The effective diffusion rates were found to correlate with the amount of unfrozen portion of the samples. This suggests that ions move mainly through the unfrozen portion around the ice crystals. Fast- and slow-frozen samples exhibited significantly different effective diffusion rates at -15 degrees C, which might be due to differences in size and orientation of ice crystals. Zn+2 ions moved slower at -15 degrees C than at -8 degrees C.