Pulsed electric fields and temperature effects on drying and rehydration of red beetroots

The effect of the pulsed electric field (PEF) pretreatment on convective drying of red beetroot tissue was investigated at the drying temperatures T-d in the interval 30-100 degrees C. The degree of material damage Z under the PEF and thermal treatment was studied. Dependence of the electrical characteristic damage time tau(E) on the electric field strength E and the thermal characteristic damage time tau(T) on temperature T-d is discussed. The drying rate is shown to be maximal for highly disintegrated tissues; PEF pretreatment allowed reduction of the drying temperature by 20-25 degrees C. PEF pretreatment results in greater degree of tissue shrinkage and hence increase in rehydration time; however, the textural properties of rehydrated samples with and without PEF treatment are seen to be similar. The benefit of PEF pretreatment for drying at moderate temperatures with preservation of colorants is also demonstrated.