Saccharomyces cerevisiaeStructural Changes Induced by Pulsed Electric Field Treatment

Saccharomyces cerevisiae(ATCC 16664) inoculated into commercial heat sterilized apple juice was treated with high intensity (40 kV/cm) pulsed electric fields (PEF). Transmission electron microscopy (TEM) observations of PEF treated S. cerevisiaecells provided little evidence to support the electroporation inactivation theory as the major mode of yeast inactivation. TEM micrographs of PEF treated S. cerevisiaefrom apple juice exhibited frequent disruption of yeast cellular organelles and almost total absence of ribosome bodies. Damaged organelles and lack of ribosomes suggests cytological disruption as an alternative inactivation mechanism to the accepted electroporation theory. Naturally occurring bud scars formed through propagation of daughter yeast cells from mother yeast cells were differentiated from PEF induced scars with TEM observations.