مقایسه ویژگی های کیفی برگه خرمالو خشک شده به دو روش هوای داغ و مادون قرمز

Abstract

Introduction: One of the most important aspects of food preservation is controlling the moisture of material such as fruits.Dryingis considered as important method to controlbacteriasafely using reduction of moisture. The hot air drying method has been widely adopted in manufacturing of conventional dried food.Nowadays, Infrared radiation (IR) has significant advantages over conventional drying. Among these advantages,higher drying rates giving significant energy savings anduniform temperature distribution giving a better quality of product. Therefore, it can be used as an energy saving drying method. Earlier attempts forapplying infrared waves to drying of agricultural materials have been reported in the literatures, such as banana, onion, garlic, apple, corn, pomegranate seeds and peach. The persimmon (Diospyros kaki) is native to East Asia, most likely China. This fruit has very short shelf-life; it is due to thehigh soluble tannin content of the fruit during storage even at refrigerated conditions. The persimmon is mainly eaten fresh, but can be dried.Duringdrying the tannin cells coagulate, so astringency is removed and the sugars in the fruit exude to the surface where they crystallize, thus producing a sweet, candied product. The objective of this study was to examine the drying behavior of the far infrared and hot- air drying of persimmon slices by comparing the physical quality. Materials and methods: Persimmon (Diospyros kaki) used in this study was purchased from a local market (KhorasanRazavi, Mashhad). The whole samples were stored at 4°C. The initial moisture content of persimmon was found to be 78.2 kg H2O/kg moisture. The sampleswerecut into 5mm slices using a cutting machine and were dried to 10% final moisture (wet basis). - Infrared dryer setup: Infrared (IR) dryer used in this research was equipped with IR lamp (1300W). Persimmon slices were placed in a single layer on the drying tray and heated from one side. Thermocouples (Type K) were inserted at the center of persimmon slice.IR drying tests were conducted with final product temperatures controlled at 50°C, 60°C and 70°C. -Hot air dryer setup: Persimmon slices were arranged in a single layer on the trays and dried in cabinet dryer at material temperatures of 50°C, 60°C and 70°C.Air velocity in the dryer was 1.5 m/s. -Quality evaluation: Persimmon slice drying characteristics including rehydration ratio, color parameters, shrinkage, texture and sensory properties were investigated ResultsandDiscussion: It is clear that the moisture content and drying rate decrease continuously with drying time. The drying rate was rapid during the initial period but it became very slow at the last stages of dryingprocess. Persimmonslices dried with hot-air and infrared dryer at temperatures 60 and 70◦c respectively, had a maximum rehydration ratio. In general, infrared drying showed significant effect on L value (p<0.05) and slices dried in 70°C were found to have maximum L values (64.33).Due to the reduction of browning reactions byIR heating, b vales of samples were reduced. The lowest content of shrinkage was observed in infrared dried samples at 50°C. Results of sensory evaluation showed that infrared dried samples are more acceptable and obtained higher score comparing to hot-air dried samples. Conclusion: In conclusion, our results showed thatthe IR drying had much higher drying rate compared to the hot air drying. Its drying rate increased remarkably with increasing of the radiation intensity. Infrared drying of persimmon slices is an effective method of water removal. Drying with application of infrared energy is much faster than convective drying(under equivalent parameters). Beside, IR radiation did not cause any negative impact on characteristics and quality dried sample. Besides, IR drying methods dramatically reduced the drying temperature.