Browning prevention in rehydrated freeze-dried non-blanched potato slices by electrical treatment

Freeze-drying (lyophilization) has many advantages. The color of the freeze-dried product resembles that of the fresh tissue, in contrast to the frequently darker color resulting from conventional oven-drying. However, freeze-dried non-blanched potato slices suffer from considerable browning following rehydration. Electrical treatment of the fresh tissue (40V/cm for 1min) without heating and before lyophilization reduced its browning after rehydration: L* values (lightness) of the untreated and electrically treated rehydrated tissues were 50.4±0.3 and 84.3±0.8, respectively. Image processing revealed that the porosity of the freeze-dried potato is not significantly influenced by the prior electrical treatment. Compression of any of the treated freeze-dried specimens always yielded characteristic sigmoid stress-strain curves. The freeze-dried blanched potato specimen was tougher than both the freeze-dried fresh potato and its electrically treated counterparts.