Some quality properties of kumquat (Fortunella margarita Swing.) dried with different drying methods and their changes during storage

In this study, dried kumquat production was aimed using different drying methods from "Nagami" variety. The dried kumquat slices were stored at room conditions for 4 months and the product quality and stability were investigated. In this scope, the sliced fruits were dried using four different drying methods including hot air, vacuum, ultrasound assisted osmotic pre-drying with hot air and microwave assisted hot air drying with debittering by water blanching and without pretreatment. Total dry matter, water activity, colour properties [L*, a*, b*, C (chroma), H° (hue angle), TCC (total colour change), BI (browning index)], rehydration ratio, total phenolic, total carotenoid, ascorbic acid, HMF (5-hydroxymethylfurfural), organic acid and flavonoid contents and antioxidant activity [DPPH (2,2-diphenyl-1picrylhydrazyl) radical scavenging activity and ORAC (oxygen radical absorbance capacity)]of unblanched, blanched and dried fruit slices were determined. The total dry matter and water activity values of the dried samples were varied between 87.09-88.34 and 0.236-0.280, respectively. It was determined that, ultrasound assisted osmotic pre-drying with hot air drying method in terms of L*, a*, H° and BI values and microwave assisted hot air drying method in terms of b*, C and TCC values were provided higher colour stability of the kumquat slices than other drying methods. It was determined that the samples dried by hot air and microwave assisted hot air drying methods with pretreatment had the highest rehydration ratio. The drying methods with pretreatment were lead to a significant loss of bioactive properties of kumquat slices compared to the drying methods without pretreatment. Generally, vacuum drying method gave the best results in terms of investigated functional properties. The highest total phenolic, ascorbic acid, IC50, organic acid and flavonoid components values were determined in the samples dried by vacuum drying method without pre-treatment. Ultrasound assisted osmotic pre-drying with hot air drying method with pretreatment was significantly reduced the content of total phenolic, carotenoid, ascorbic acid, HMF, organic acids and flavonoid components of kumquat slices. L*, b*, C, H° and ascorbic acid values of dried samples which were stored in room tempetrature for 4 months decreased, while water activity, HMF and TCC values increased. According to the results of the research, most suitable methods which can be used in the production of dried kumquat for high bioactive component content and antioxidant properties, were determined as vacuum drying, hot air drying and microwave assisted hot air drying without pre-treatment, respectively.