2.5. Scanning electron microscopy analysis
Freeze-dried samples were cut with a razor blade and cut surface samples were prepared by sticking onto double-sided adhesive tape attached to a circular specimen stub. The samples were viewed using an environmental scanning electron microscope (ESEM) (Quanta200F, FEI Deutschland GmbH, Kassel, Germany) at 30 kV and 3.0 spot size (Chen et al., 2012).