Effect of Dehydration Techniques on the Quality of Onion Slices

Quality of dehydrated onion slices produced by combination drying (CD) technique was investigated. Appearance, colour, flavour and rehydration characteristics of CD onion slices were compared with those of hot-air dried (HAD) and freeze-dried (FD) products. The total flavour strength of the product was significantly affected by drying processes. The HAD onion slices exhibited shrinkage, case-hardening, browning and poor rehydration properties (rehydration lime 6.5 min in cold water and rehydration ratio 1:1.5) and less volatile content (0.06%). The FD sample appeared wholesome, showed more retention of volatile content (0.13%) and good rehydration properties (rehydration lime 1 min in cold water and rehydration ratio 1:1.8). The CD sample was comparatively superior to HAD and nearer in quality to FD in appearance, colour, rehydration properties (rehydration time 4.25 min in cold water and rehydration ratio 1: 1.7) and volatile content (0.11 %).