Effect of pretreatment temperature and time on drying characteristics of broccoli and cauliflower

In this study, broccoli and cauliflower were dried in a cabinet dryer in order to examine effect of pretreatment temperature and time on drying characteristics of broccoli and cauliflower. At first, it was determined the moisture contents of broccoli and cauliflower which bought from a supermarket in İstanbul. As a result of determination of moisture, dry matter of broccoli and moisture contents were determined 12,92% and 87,08%; dry matter of cauliflower and moisture contents were determined 9,81% and 90,19%, respectively. Three different samples were prepared by slicing approximately 100 grams of both vegetables. First sample was not pretreated at all. The second sample was pretreated in water at 80°C for 1 minute and then dried with hot air. The third sample was pretreated in citric acid solution at room temperature for 1 minute and then dried with hot air. Drying experiments were done with hot air at 45, 55, 65 and 75°C for both vegetables. For the other drying experiments, the samples were pretreated 1, 2, 3, 4 and 5 minutes at a fixed temperature of 80°C and then dried with hot air at 65°C. In the next step, fixing the pretreatment time to 2 minutes, samples were pretreated in hot water and citric acid solution at 40, 60 and 80°C. Then, the samples were dried with hot air at 65°C. In this way, effect of pretreatment temperature and time to drying parameters of broccoli and cauliflower was investigated. As a result of the drying experiments, at first, drying curves were drawn and moisture content was observed to decrease over time. Increasing the temperature of drying air, drying time is shorter. Also it was observed that drying time of samples pretreated is shorter than the other samples. This determination is more remarkable for dried product which pretreated with hot water than the product which pretreated with citric acid solution. Also while pretreatment temperature and time are increasing, drying time is shorter. The drying data were fitted to seven mathematical models (Newton, Page, Henderson and Pabis, Logaritmic, Two-term, Wang and Sing and Midilli et al.). Coefficients, regression coefficient (R2), chi-square (χ2) and root mean square error (RMSE) values were calculated for each mathematical model and compared with each other. The Midilli et al. model was found to be most suitable in describing the drying characteristics of broccoli and cauliflower. Because the Midilli et al. model has given maximum R2, minimum χ2 and RMSE values. Effective moisture diffusivity and activation energy values were calculated at 45, 55, 65 and 75°C for both vegetables. The results match with similar studies done before. Finally, rehydration rate of the samples which were dried at 65°C were analysed. Increasing the temperature of rehydration, rehydration rate is higher and it was observed that rehydration rate of pretreated samples is higher than untreated samples.