The impact of ultrasound and steam blanching pre-treatments on the drying kinetics, energy consumption and selected properties of parsley leaves

In current study the influence of ultrasound pre-treatment and drying conditions (microwave power, air temperature) was analysed by the means of drying kinetics, energy consumption and selected quality properties of dried parsley leaves. Ultrasound treatment (US) was compared with conventional treatment – steam blanching. In comparison to untreated material, ultrasound applied at 21 kHz, 12 W/g, contributed to significant reduction of the drying time up to 29.8%. Moreover, the energy expenditures were reduced maximally by 33.6% for parsley dried at 30 °C and 300 W. For this sample the colour retention was the highest, as well. In turn, steam treated parsley was dried maximally by 28.9% faster and thus specific energy consumption decreased to 72.0% of the value for intact leaves when 20 °C and 300 W were set. The influence of pre-drying treatment on the quality properties depended on the drying conditions. Pre-drying treatment (US, blanching) did not affect the lutein content significantly, whereas the most considerable increase of chlorophyll a and b resistance and their relative concentration (Chl a/b ratio) was achieved in US-treated leaves dried at 30 °C and 100 W. The utilisation of drying pre-treatment and dehydration parameters should be considered with respect to further utilisation of dried parsley leaves. Nonetheless, sonication is worth to be taken into account due to a significant reduction of energy expenditures and an improvement of resistance of bioactive components.