Accumulation of intracellular trehalose and lactose in Lactobacillus plantarum WCFS1 during pulsed electric field treatment and subsequent freeze and spray drying

Abstract

Survival of bacteria during drying processes is required for products such as probiotics or starter cultures. In earlier studies high intracellular trehalose concentrations have been related to processing robustness during freezing and drying for several cell types. In this study we evaluated pulsed electric field (PEF) pre-treatment to increase intracellular trehalose in Lactobacillus plantarum WCFS1 and subsequent survival during freeze drying and storage in a trehalose matrix. Surprisingly, despite increased intracellular trehalose by PEF pre-treatment no enhanced survival was observed after drying and storage. Additional analysis of intracellular trehalose before and after freeze drying and spray drying revealed that during the drying process intracellular trehalose concentrations increased. Due to this increase the intracellular trehalose concentrations in the PEF pre-treated and control samples did not differ anymore. To explain what happens during the drying processes, results for trehalose were compared to similar experiments with lactose. A remarkable difference was observed between transfer of trehalose and lactose into cells during the freezing step before freeze drying, while both disaccharides gave similar cellular protection when used as freezing and drying matrix. Generated knowledge on transport of disaccharides into bacterial cells during freezing and drying can benefit processing of living bacterial formulations.