Transport phenomena in immersion-cooled apples

The effect of immersion chilling and freezing (ICF) process parameters (solution temperature, concentration and composition, initial food temperature) on heat and mass transfer was studied on apple cylinders dipped into a sodium chloride aqueous solution, with particular emphasis on the unsteady-state period (first hour of treatment). Food behaviour was characterized for various thermal processes; the levels of salt impregnation in chilling and supercooling conditions, at 2 degrees C and -10 degrees C, respectively, were similar (3% i.m. after 1 h of processing) and much higher than in freezing at -17.8 degrees C (0.6% initial mass for the same processing time). Further control of solute entrance in freezing conditions could be achieved through food surface treatments, including precoating with cold water before ICF; use of a complex immersion solution containing a high molecular weight of solute; quick freezing of the outer food layer. Above all, the frozen water fraction inside the food was found to be an important factor governing solute entrance in freezing conditions.