The effects of different drying methods on drying properties and quality in drying of seedless grapes

Drying is the process of a controlled removal of the moisture that the products contain. In this study, sultani seedless grapes were dried, drying times, mathematical modelling, color changes were determined and chemical analyzes (SSC, pH, Titration acidity) were performed. The drying process was carried out in six different methods. These are drying in oven, vacuum oven, laboratory type convective dryer, temperature controlled microwave dryer, sun and shade. The grapes were dried in three recurrence with and without potassium solution. Temperature-controlled microwave drying at 55 ºC and 60 ºC, while other drying methods are carried out at 60 ºC, 65 ºC and 70 ºC. The longest drying time was 649 hours in without potassium solution drying in the shade and the shortest drying time was 10.5 hours at 70 ºC with potassium solution in the laboratory type convective dryer. 5 equations were used for mathematical modeling. These were Page, Jena Das, Midilli-Küçük, Lewis and Yağcıoğlu. According to the "b" yellowness value, it was determined that there is no difference between fresh grapes and laboratory type convective dryer without potassium solution in 70 º C, and the value was found as 2.23. The value of the closest SSC to fresh grapes has been determined as 75.00 at 65 º C without potassium solution in vacuum oven. The pH value at 65 ºC without potassium solution in oven was determined the same with fresh grapes and its value was 3.31. Among all drying methods, temperature controlled microwave drying method was determined as the most suitable method for sultani seedless grape drying in terms of color criteria.