Evidence on the role of protein biosynthesis in the induction of heat tolerance of Lactobacillus rhamnosus GG by pressure pre-treatment.

It was the aim of this work to evaluate, whether and to which extent heat resistance of Lactobacillus rhamnosus GG is affected by mild pressure treatments prior to exposure to lethal temperatures, such as during spray-drying. It was observed that cells pressure pre-treated at 100 MPa at 37 degrees C for 10 min showed higher survival than untreated cells when exposed to heat challenge at 60 degrees C. To gain more insights on the cellular mode of action of pressure induced heat tolerance, flow cytometric analysis was applied in combination with functional dye LIVE/DEAD BacLight bacterial viability kit. Dot plot analysis showed that a lower degree of membrane damage was observed at pressure pre-treated cells upon heat treatment at 60 degrees C for 3 min. Evaluation of heat inactivation kinetics of cells pressure treated in the presence of chloramphenicol, a protein synthesis inhibitor, pointed out the potential contribution of pressure-induced protein biosynthesis in the enhancement of bacterial heat tolerance.