Comparison of inactivation pathways of thermal or high pressure inactivated Lactobacillus rhamnosus ATCC 53103 by flow cytometry analysis

The effect of thermal and pressure treatments on Lactobacillus rhamnosus ATCC 53103 was evaluated by flow cytometric analysis in conjunction to standard cultivation techniques. A double staining technique with fluorochromes carboxyfluorescein diacetate (cFDA) and propidium iodide (PI) revealed that depending on temperature regime used heat-killed cells had different fluorescence behaviors. Cells killed at 60 °C were not stained at all whereas heat treatment at 75 °C resulted in a single population entirely labelled by PI. These findings indicated that thermal-induced cell death was achievable with or without membrane degradation. Hydrostatic pressures beyond 400 MPa inactivated L. rhamnosus ATCC 53103 in a different way. It was observed that the irreversible damage of the membrane-bound transport systems could be largely accounted for the cause of high pressure-induced cell death.