Since not only the step of drying affects the final quality of dehydrated fruits and vegetables, it was necessary to
know the influence of pre-treatments such as blanching. In general, this procedure is carried out to inactivate
enzymes that could cause a significant deterioration of the product throughout the storage period. Therefore, in the
first stage of the work, a study on the effectiveness of different pre-treatments, conventional and with US, on the
inactivation of the POD and the PME and losses by leaching during blanching of carrot was done. Hardly any
enzyme inactivation was observed in bath of US and in the assays with probe at low temperatures. However, with
US probe and generation of heat, the highest values of enzyme inactivation (90 and 50% for POD and PME,
respectively) were achieved with a treatment of 15 min and temperature up to 70 °C. As an example, Figure 1
depicts the inactivation of POD. The results obtained showed the combined effect of the US and the temperature and stressed the difficulty of identifying the mechanisms of enzyme inactivation by US, since cavitation can involve
various mechanical and chemical effects. In addition, there are numerous extrinsic and intrinsic factors that can
affect the process resulting in enzyme activation or inactivation (Cruz et al., 2006).
From the results obtained in this study, we could infer that US are particularly suitable as an alternative to
conventional treatments LTLT (low temperature long time), which could originate products with lower textural
modifications. Thus, attending enzymatic inactivation and losses by leaching, similar results were obtained for
LTLT treatments at 60 °C for 40 minutes and with US probe for 10 minutes at temperatures up to 60 °C. In the
latter, the use of the probe resulted in a reduction of 75% in pre-treatment time, which could represent significant
energy savings. However, taking into account the enzymatic inactivation, among all the pre-treatment tested, the
most effective were the corresponding to steam and boiling water during short time (HTST), which are the most
often used in the industry.