The survival and stability of Lactobacillus rhamnosus GG as affected by particle formation during spray drying and spray-freeze drying

Abstract

Droplets of the same composition can be transformed into particles with varying properties by different drying methods and conditions. In this study, Lactobacillus rhamnosus GG (LGG) encapsulated in trehalose matrix was produced using a micro-fluidic jet spray dryer and a micro-fluidic spray-freeze tower, respectively, with 10 and 30 wt% protectant. The spray-freeze-dried microparticles between 139.9 and 152.9 μm showed porous morphology with airy structure, contrasting the spherical, smooth, and dense microparticles produced by spray drying with relatively small size (75.1–110.4 μm). The encapsulated cells formed clusters in spray-dried microparticles. The high-solids protectant of 30 wt% resulted in high survivals of LGG (35.40% and 49.58%) with minimal cellular membrane damages and relatively high metabolic activity in both spray drying and spray-freeze drying. Compared to the 10% spray-dried particles with a survival of 30.04%, a lower survival of 12.56% and more substantial cellular injuries were observed for the 10% spray-freeze-dried particles, reflecting the damage to cells from water crystallization during freezing. Both spray-freeze-dried samples exhibited much better stability during storage and in vitro digestion than the spray-dried samples, which could be linked to the low residual moisture after dehydration. Considering stresses experienced by LGG cells, spray-freeze drying offers a promising alternative to freeze drying for producing active lactic-acid-bacteria powders, whereas the intensity of stresses under the tested spray-drying conditions remained challenging for achieving the maximal retention of the viability and functionality of the bacteria.