Modeling and optimization of Effective factors in drying on quality properties of black raspberry (Rabus fruticocus L.) with response surface methodology

The main target of this research is drying raspberries in a Microwave assisted fluidized bed dryer. In orderto evaluate and predict the quality properties of this fruit, Response Surface Methodology (RSM) was used. In this research, the effects of five variables: power of microwave (0, 300 and 600 W), temperature (55, 70 and 85 C), air flow rate (15, 20 and 25 m/s), starting time of microwave input (from the moment when the moisture content decreased until 334, 400 and 466 g water per 100 g dry matter) and amount of material (50, 100 and 150 g) on the rehydration capacity and loss of anthocyanins content were studied. Experiments were designed according to Central Composite Rotatable Design with these five factors each at three different levels, including central and axial points. With respect to the dependent variables, both linear and quadratic effects of all of the five independent variables on Rehydration Capacity and loss of anthocyanins content were found to be significant. For each response, second order polynomial models were developed using multiple linear regression analysis. Analysis of variance (ANOVA) was performed to check the adequacy and accuracy of the fitted models. According to our results, the optimal point for both characteristics were as follows: microwave power 600 W, temperature 74, the air flow rate 3/22 meters per second and 53 grams of the substance, starting from the moment the microwave 466 percent moisture content was reduced. Model to predict the dependent variables with empirical results obtained were very close.