Microwave Assisted Vacuum Drying of Thompson Seedless Grapes: Analysis of Characteristics And Kinetic Modelling

Shritama Mukhopadhyay*, Ratna Dutta**, Arunima Adak***
*-** Department of Chemical Engineering, Jadavpur University, Jadavpur, Kolkata, India.
*** Department of Chemical Engineering, Calcutta Institute of Technology, Howrah, West Bengal, India.
Periodicity:October - December'2019


A laboratory Microwave Assisted Vacuum Dryer (MAVD) was used in the present study to investigate the drying behaviour of Thompson seedless grapes under different microwave power levels, vacuum levels and thickness of grapes. It resulted in very low drying time as moisture diffusivity in grapes under MAVD process is few orders of magnitude more than that noted in sun-dried method. Drying kinetics study was done and the non-linear empirical model was found to be best fitted for describing the drying behaviour in this case. The effect of variation of process variables was studied and with respect to time efficiency and acceptable product quality, 400 mm Hg vacuum, 350 watt power and 1/3rd sliced grape samples provided best operating condition. Effect of hot and cold dipping pre-treatment on drying characteristics was also tested. Combination of ethyl oleate and K2CO3 as dipping solution (cold dip) worked best and gave lower drying time (13.454 min) than untreated grapes (23.19 min). Rehydration ratio and total soluble solid content (Brix value) were measured to indicate product quality of raisins. The rehydration ratio of dried seedless grapes was found to be 1.27±0.1 (without dipping) and 1.29±0.1 (with dipping) which are higher than the sun dried products. Brix value was obtained as 76.2 at 350 watt for 1/3rd sliced grapes, which is higher than the sun-dried raisin. Thus, results revealed that the MAVD process would be a promising alternative to conventional drying systems for raisin production within lesser time and with improved energy efficiency.


Drying Kinetics, MAVD, Thompson Seedless Grapes, Moisture Diffusivity, Dipping.

How to Cite this Article?

Mukhopadhyay, S., Dutta, R., and Adak, A. (2019). Microwave Assisted Vacuum Drying of Thompson Seedless Grapes: Analysis of Characteristics and Kinetic Modelling. i-manager's Journal on Chemical Sciences, 1(1), 38-52.


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