Cyclic air temperature drying of guava pieces: Effects on moisture and ascorbic acid contents

Moisture and ascorbic acid (AA) contents of batch-dried guava samples were measured under several cyclic temperature profiles of the drying air maintained at constant humidity. A two-stage heat pump dryer was used to obtain the desired cyclical variation of the drying temperature while keeping other drying air parameters constant. Experimental results on AA degradation of guava during drying were found to follow first-order kinetics for both isothermal and non-isothermal drying air conditions. Cyclic air-temperature drying was observed to yield higher retention of AA. Using a simplified model previously proposed for storage of foods, representative equivalent temperatures were computed for each time-temperature profile to correlate the AA degradation results to corresponding air temperature under isothermal conditions.