PhD defence

Pulsed electric field pre-treatment for drying of living bacteria

Summary:

Bacteria are commonly used in food industry as starter cultures or probiotic supplements. These bacteria can be stored in the powder form to prolong their shelf life. However, during the drying process bacterial inactivation occurs due to thermal and dehydration stresses. In this thesis we focused on a pre-treatment for the bacteria to increase their survival during subsequent drying processes. We provided a proof of principle that pulsed electric field (PEF) pre-treatment can be used to increase intracellular protective solutes concentrations in bacteria. This PEF treatment resulted in permeabilization of the cellular membrane upon which protective molecules in the PEF medium can diffuse into the cell. Furthermore, we showed that PEF pre-treatment can lead to increased drying robustness of bacteria when the bacteria are dried in a reconstituted skim milk medium. These insights can be used to develop and optimize drying processes aimed at high bacterial culture viability.