Mathematical modeling of microwave-assisted convective heating and drying of grapes

Abstract

This research studied the processing performance and product quality of Thompson seedless grapes dried using microwave-assisted convective hot air drying as well as the effect of blanching and dipping pretreatments. Two pretreatment methods were compared, dipping into 2% ethyl oleate (V/V) and 5% potassium carbonate solution (m/V) at 40℃ for 3 minutes and steam blanching at 90℃ for 140 s, to accelerate drying rate and inactivate PPO aiming to improve drying rate and product color. Pretreated grapes were dried in a microwave-assisted convective dryer at 0.25 W/g specific power and 60℃ air temperature. In this study dielectric and physical properties of grapes were calculated using descriptive equations for fruits and vegetables. Semi-theoretical models were used to describe the drying curves of both pretreated and untreated grapes. Center and near surface temperature profile of grapes was obtained using fiber optic probes. Experimental center temperature was modeled using one dimensional heat equation and was simulated using Partial Differential Equation toolbox of Matlab. The results showed that the maximum difference between experimental and predicted values were 4℃ which occurred at the initial heating up period. It has been observed that dipping into solution had no effect on drying rate whereas steam blanching significantly reduced the drying time and produced product with desirable color.

Keywords: Microwave, drying, grapes, mathematic modeling, thin-layer, curve fitting
DOI: 10.3965/j.issn.1934-6344.2008.02.046-054
Citation: Gokhan Bingol, Zhongli Pan, John S. Roberts, Y. Onur Devres, Murat O. Balaban. Mathematical modeling of
microwave-assisted convective heating and drying of grapes. Int J Agric & Biol Eng. 2008; 1(2): 46－54.