Effect of various drying techniques on quality properties of organic blueberry fruit

ABSTRACT EFFECT OF VARIOUS DRYING TECHNIQUES ON QUALITY PROPERTIES OF ORGANIC BLUEBERRY FRUIT GÖK, Gülşah M.Sc. in Food Engineering Supervisor: Prof. Dr. Medeni MASKAN Co-Supervisor: Assoc. Prof. Dr. K. Bülent BELİBAĞLI December 2019 81 pages The effects of convectional air and microwave-convectional (hybrid) drying methods, and ultrasound and osmotic dehydration pretreatment on drying characteristics and some quality parameters of organic blueberry were investigated. Convectional drying was performed at 60, 70, and 80 °C temperatures. Hybrid drying was performed at 150, 180 and 210 W power levels at 60 °C constant air temperature. Blueberries were exposed to a simultaneous ultrasound and osmotic dehydration pretreatment. An organic apple juice concentrate (70 °Brix) was used as the osmotic medium. The ultrasound pretreatment extended the drying process. Hybrid drying resulted in shorter drying times compared to air drying. Increasing temperature in air drying and microwave power in hybrid drying increased the drying rates. The best fitting model for all drying conditions was determined as Midilli et al. model. Higher total phenolics content (TPC) and antioxidant activity (AA) levels were obtained by the hybrid drying compared to hot air method. The highest TPC and AA values were obtained at 180 W hybrid drying, while the lowest values were obtained at 70 oC air drying. Application of ultrasound and osmotic dehydration treatment led to a significant decrease in TPC and AA. Color values were generally similar to each other. As a conclusion, hybrid drying can be considered as an alternative dehydration method for the drying of blueberries. Key Words: Organic Blueberry, Drying, Ultrasound, Phenolics Content, Microwave