Drying kinetics and quality aspects of bitter gourd (Momordica charantia) dried in a novel cabinet dryer

Abstract

An attempt was taken to investigate the effect of drying air temperature and slice thickness on the drying kinetics and quality of bitter gourd (Momordica charantia) dried in a novel cabinet dryer (HSTU Fruit and Vegetable Dryer). Fresh bitter gourd was sorted, cleaned, and sliced at 4 mm, 6 mm, and 8 mm thickness. All the samples were blanched in boiling water at 100°C for 3 mins. Then the slices with an initial moisture content of 96.47±0.6% were dried, spreading as a thin layer in the trays of the cabinet dryer using three drying air temperatures of 60, 70, and 80°C until the desired final moisture content (MC) of 4.66±0.4% was obtained. The results indicated that the shortest drying time (2.08 hrs) was required by the sample of 4 mm thickness, which was dried at 80°C to reduce moisture from 96.47±0.6% initial (wet basis, wb) to 4.66±0.4% final moisture (wb). The sample of 8 mm thickness dried at 60°C took the longest drying time (6.67 hrs). The higher drying rate (34.32 gm H2 O/min.cm2) was noticed at a constant drying rate period in the case of a 6 mm thick slice at 70°C. Whereas a lower drying rate (9.29 gm H2 O/min.cm2) was observed for drying 8 mm slices using 60°C air temperature. Even though, the effect of blanching on drying characteristics of bitter gourd was not noticed so much, the drying rate was found to be increased slightly of pretreated bitter gourd thus drying time was shorter. A comparison on colour analysis of both fresh and blanched bitter gourd showed that a 6 mm slice dried at 70°C was found better in retaining green colour than other samples. The rehydration ratio (6.63±0.62) and the percentage of water uptake (86.75±0.58) of rehydrated pretreated bitter gourd were also higher in a dried sample of 6 mm. Therefore, pretreated bitter gourd is suggested to dry quickly using 70o C in a cabinet dryer slicing at 6 mm thickness to obtain a better quality dried product.