Strawberry drying: Development of a closed-cycle modified atmosphere drying system for food products and the performance evaluation of a case study

Abstract

ABSTRACTIn the present study, a closed-cycle modified atmosphere drying (CC-MAD) system was developed as an alternative drying technique to facilitate drying processes for agricultural commodities appropriate to highly humid and sunny regions with a better quality. An absorption dehumidifying system was designed for working pseudo-continuously with the most efficient absorbent in terms of moisture absorption, desorption rate, and capacity. The system, assisted by a solar panel for absorbent regeneration, was tested, while its optimum working condition was determined by strawberry drying. This unique process was comparatively carried out using hot-air and freeze-drying techniques in terms of processing time and final product quality. Strawberry slices (5 mm thickness) were dried successfully using CC-MAD. The optimum drying conditions of CC-MAD were determined as drying temperature of 60°C, drying air/gas velocity of 3 m/s and drying medium oxygen level of 9.47%. The loss of ascorbic acid was significantly reduced by CC-MAD technique. These losses were found to be 2.9, 6.9, 27.2, and 23.8% by freeze-drying, CC-MAD, hot-air drying, and hot-air drying combined with CC-MAD, respectively. The total monomeric anthocyanins loss was also significantly reduced by the CC-MAD technique (20.3%), in a similar way to that of freeze-drying (18.1%) in comparison with hot-air drying (40.4%). In addition, CC-MAD (12,446 kJ/kg fresh product at 4 h drying time) is three times more advantageous in terms of energy cost compared with freeze-drying (30492.8 kJ/kg fresh product at 24 h drying time) and six times faster in terms of drying time. This new drying system can be used as an alternative to freeze-drying in the drying of foods, especially in products sensitive to oxidation.