Effects of low temperature blanching on texture,microstructure and rehydration capacity of carrots

The effect on quality of stepwise blanching (first 10 min at 65 °C, 50 min holding time, and 1 min at 95 °C) prior to drying of carrot slices was compared with conventional blanching (95 °C, 1 min). As quality parameters, rehydration capacity (effective diffusivity D_e, equilibrium moisture content W_e), texture (puncture test) and microstructure (SEM and Cryo‐SEM) were chosen. Non‐significant differences were found between the W_e of stepwise blanched samples and conventionally blanched ones, both values being similar to the moisture content of fresh carrots. D_e of conventional blanched carrots was higher than for stepwise blanched ones. Maximum force of stepwise blanched samples was higher than those of conventionally blanched ones and not significantly different from fresh carrots. Microstructural observations showed that stepwise blanching preserved cell to cell contacts better than conventional blanching; this fact was attributed to pectin‐methyl‐esterase activation at 65 °C, resulting in the differences in the maximum force between both treatments. Conventionally blanched samples tended to separate along their cell walls, forming voids among the phloem parenchyma cells. These voids would be filled with water during rehydration, thus showing the slightly higher W_e and the higher D_e for conventionally blanched carrots. Copyright © 2005 Society of Chemical Industry