EFFECT OF COMBINATION DRYING ON THE PHYSICO-CHEMICAL CHARACTERISTICS OF CARROT AND PUMPKIN

Abstract

The quality of dehydrated carrot and pumpkin pieces produced by combination drying employing partial freeze-drying and hot air-drying were investigated. The drying rate, the total energy requirement and the physico-chemical properties of the combination dried (CD) products were compared with those of hot air-dried (HAD) and freeze-dried (FD) products. The total carotenoid content of the two vegetables (1050 ppm and 160 ppm) was significantly affected by drying processes. Destruction of carotenoids during storage at different temperatures was less in the CD samples. The HAD vegetables exhibited shrinkage, case hardening and poor rehydration (25 and 28 min in cold water, rehydration ratio 1:2.6 and 1:2.9, respectively). The FD vegetables appeared wholesome, porous, well formed with excellent rehydration features at room temperature (rehydration time 2 and 3 min in cold water, rehydration ratio 1:7 and 1:6.9, respectively). The CD vegetables were comparatively superior to HAD products and were nearer in quality to FD products with respect to appearance, rehydration (9 and 10 min in cold water, rehydration ratio 1:5 and 1:4, respectively). The drying time and total energy for CD processing was 50% less than for FD but similar to HAD. The combination dehydration process is effective in obtaining high quality dehydrated vegetables.