New drying process for lactic bacteria based on their dehydration behavior in liquid medium

Abstract

This study describes the different stages of optimization in an original drying process for lactic acid bacteria that allows the retrieval of dried samples of Lactobacillus plantarum with maximum viability. The process involves the addition of casein powder to bacterial pellets, followed by mixing and then air-drying in a fluidized bed dryer. The effects on bacterial viability of the a(w) of the casein powder and the kinetics of a(w) variation in the fluidized bed dryer are considered. These parameters were first studied in a water-glycerol solution and the results were then applied to the drying process. Data from the study in liquid medium were reliable in the fluidized drying stage, insofar as optimal viability was achieved for similar dehydration times (16-50 min in liquid medium, and 30 min in the fluidized bed dryer). However, when the powder was mixed rapidly with bacteria, the level of destruction differed from that observed in liquid medium. Viability was up to 70% when the a(w) of water-glycerol was 0.55, whereas it was only 2.1% when the a(w) of the casein-bacterial mix was 0.64. The predictive capacity of dehydration in liquid medium is discussed with regard to the permeability of cells to external solutes. The new process allowed 100% survival of L. plantarum after complete drying (final a(w) < 0.2). However, when used for the desiccation of L. bulgaricus, these parameters achieved a viability of less than 10%.

Effect of water activity and protective solutes on growth and subsequent survival to air-drying of Lactobacillus and Bifidobacterium cultures

“…The literature reports survival levels of L. plantarum to air-drying ranging from 10% to 97% (Kets et al 1996;Linders et al 1997b;Mille et al 2004), and data from this study are in line with these results.…”

“…The rate of drying affects survival to air-drying (Mille et al 2004;Paul et al 1993;Linders et al 1997b). Under our experimental conditions, a nine-fold concentration in solids had occurred after 3 h of drying, but the a w was still high (0.88).…”

Towards a maximal cell survival in convective thermal drying processes

“…In this regard, cells from the stationary phase have been widely used in all kinds of drying processes, e.g. spray drying , fluidized bed drying (Mille, Obert, Beney, & Gervais, 2004), vacuum drying (Tymczyszyn, del Rosario Diaz, et al, 2007a), convective drying in a tunnel as well as freeze drying (Bozoglu, Ozilgen, & Bakir, 1987;Costa, Usall, Teixido, Garcia, & Vinas, 2000;Miyamoto-Shinohara et al, 2000). This improved stress resistance exhibited by cells from the stationary phase is considered a natural result of triggering the stress responses upon the deprivation of nutrients and accumulation of toxic metabolites during the stationary phase.…”

Influence of lyophilization, fluidized bed drying, addition of protectants, and storage on the viability of lactic acid bacteria

“…Focusing on fluidized bed drying thermal inactivation encountered during spray drying (Corcoran et al 2004) can be minimized by applying gentle process conditions, thus dehydration inactivation remains the main problem in convective drying (Linders et al 1997a). Furthermore the consequences of oxidation are very harmful especially to the membrane structure, thus oxygen-sensitive bacterial species suffer severe damage during convective air drying (Mille et al 2004).…”