2.8. Electron microscopy
The evaluation of the surface of vegetables and the change on
cell structure after cold plasma treatment were assessed using
electron microscopy. For the vegetables, lettucewas used as a target
product. Small square pieces (approximately 1 cm per side) of lettuce
leaf were cut and placed in sterile petri dishes. For bacteria,
Nuclepore (Pleasanton, CA) filters (13 mm diameter, 0.2 mm pore
size) were inoculated on the surface with about 10 ml of the culturesolution, which were then dried under laminar flow and treated
with plasma. Samples were treated with APCP (10 min,12.83 kV), as
mentioned in Section 2.5. The pieces of lettuce and filters with
bacteria were under sample preparation for electron microscopy
after APCP treatment with a solution of glutaraldehyde (2%) and
paraformaldehyde (2%) in 0.1 M phosphate buffer (pH 7.2) was
added to the surface of the lettuce leaves and filters. Samples were
kept overnight at 4 C. The following day, the fixative solution was
replaced with phosphate buffer (0.1 M), which was in contact with
the samples for about 30 min. Afterward, samples were rinsed out a
couple of times with distilled water for 10 min each. Samples were
observed in an Environmental Scanning Electron Microscope
Quanta 200F (Field Emission Instruments, Hillsboro, OR). The
FESEM was operated in the low vacuum range, at high voltage
(10 kV), using an LFD detector (Large Field Detector).