The volume retention of MVD samples was slightly lower than that
of FD samples (Fig. 8). Although little difference was observed between
HWB and MWB samples dried using the FD method, a small difference
was observed in the volume retention of the two MVD samples.
This result is consistent with the observed dielectric values. Sample
shrinkage occurred, possibly because the internal moisture failed to
transfer in a timely manner to the sample surface during drying. The
shrinkage may have also occurred because MWB treatment increased the dielectric loss factor ε″ of the A. bisporus sample (Fig. 3); thus, the
evaporation speed for the MWB sample was higher than that for the
HWB sample during MVD, resulting in slightly higher shrinkage for
the MWB sample. In the FD samples, shrinkage may have been
prevented because the moisture inside the samples was directly
removed by sublimation of ice, leaving space and retaining the original
shape; therefore, the shrinkage was relatively limited