Effect of reversible permeabilization in combination with different drying methods on the structure and sensorial quality of dried basil (Ocimum basilicum L.) leaves

The effect of reversible permeabilization as pre-treatment before air drying at 40 °C, vacuum drying and freeze drying was investigated. The parameters of the electric treatment provoked reversible permeabilization of the tissue causing the guard cells to open stomata (65 pulses of 650 V/cm, 150 μs pulse width, 760 μs between pulses). The drying times of each of the tested drying methods were adjusted to obtain products with a moisture content of 75 g/kg. Dried samples were compared according to drying time, structural changes, rehydration capacity, colour and sensorial perception. Results showed that the PEF pre-treatment shortened the drying times 57% for air drying, 33% for vacuum drying and 25% for freeze drying. The stronger influence of the PEF treatment on air drying was also evident on tissue structure where the most noticeable differences between the untreated and PEF-treated leaves were detected. Glandular trichomes on the surface of the leaves were better preserved when PEF was applied in combination with air drying and vacuum drying whereas freeze drying, with or without PEF, damaged the trichomes. PEF-treated, vacuum dried samples were found to be the closest to fresh leaves regarding colour and smell according to the sensory panel.