Effects of closed cycle modified athmosphere drying combined with pretreatments on characteristics of some fruits

In the present research, development of closed-cycle modified atmosphere drying (CC-MAD) method is aimed as an alternative to vacuum drying techniques and also research of the applicability of CC-MAD combined with projected pre-treatments. For this purpose, strawberry, kiwi and banana fruits was preferred as material due to their perishable characteristics and low storage stabilities. The fruits were dried by CC-MAD followed by osmotic and hot air pre-drying treatments until final moisture content. This unique process carried out comparatively to hot air drying; freeze drying and only CC-MAD techniques in terms of process parameters and final product properties. Thanks to this new drying system, food-processing facilities located in high humidity and sunny regions such as the Mediterranean Coast, will be able to dry their products. The developed solar assisted CC-MAD system tested for drying fruit slices in combination with/out pre-treatments. Energy efficiency of systems and quality of dried fruits during storage were analyzed in comparison to hot air and freeze-drying techniques according to quality parameters of dehydrated foods. Moisture adsorbers were intended to use for dehumidifying of drying medium. Selected adsorbents were tested dynamically in operating conditions of developed drying system. Silica Gel (Orange Gel moisture indicator), Zeolite 4A (2,5-5 mm), Zeolite 5A (2,5-5 mm), Zeolite 13X (from 1,6 to 2,6 mm) and activated Carbon (cpur) were tested as adsorbents. Each adsorbent test was performed at 60 to 70°C (drying temperature) and 2-3 m / s in air speed for adsorption and 110 to 120°C and same air speed for desorption. Silica gel was found to be best suitable adsorbent according to the adsorption and especially the desorption test results. CC-MAD system is optimized based on Box-Behnken experimental design in system temperature, air speed and the amount of oxygen variables; the minimum ascorbic acid loss in the product, minimum browning index and drying time parameters with minimum loss of anthocyanins has been evaluated as answers of the response-surface method. Accordingly, the results indicate that the optimum temperature is 60°C, the optimum air velocity is 3 m/s and the optimum oxygen content was determined as 9,5%. All selected fruit slices were dried successfully by using direct CC-MAD (developed by this research) and CC-MAD combined with pre-drying applications. Drying curves obtained from these different drying techniques were also eliminated. The loss of ascorbic acid and total monomeric anthocyanin were significantly reduced by CC-MAD drying technique similar to that of the freeze-drying. In addition, in comparison with freeze-drying at same production capacity, energy cost of CC-MAD was ten times lower than that of freeze drying. However, notable superiority cannot be provided in color of dried strawberry slices by CC-MAD. The developed CC-MAD system should be tested in different agricultural commodities for extending food industry and integrated to the national economy.