Spray freeze drying as a novel drying process for the formulation of probiotic powders containing Lacticaseibacillus rhamnosus GG

Spray freeze drying was evaluated as a drying process for the formulation and stabilization of probiotic powders This technology combines spray freezing into cold vapour followed by rotational bulk freeze drying, and was investigated to combine the benefits of both spray drying and freeze-drying. What sets this system apart from other studies using this technology, is that the feed suspension was sprayed into cooled atmosphere instead of spraying directly into liquid nitrogen. To ensure droplet formation, a rather more dripping than spraying technique known as laminar jet break up is used, whereas other spray freeze drying techniques use binary nozzles, single fluid pressure nozzles, ultrasonic nozzles or rotary nozzles. Moreover, the principles of rotatory freeze-drying were used for bulk lyophilization which results in freeze dried microparticles instead of a freeze dried cake. This study examined the parameters related to the spraying head and their impact on bacterial viability and powder particle size. Secondly, the feasibility of dynamic lyophilization by applying rotary freeze drying to the frozen substrate was studied. Furthermore, the powder density, flow and hygroscopic properties were monitored to assess the downstream processability for industrial manufacturing. Cell reduction of at least 1,0 log CFU/g was reported, with a maximum remaining cell concentration of 7,4 log CFU/g in the dried product. The particle size of the almost perfect microspheres ranged from 532 ± 35 µm using a 300 µm nozzle orifice and 739 ± 57 µm using a 400 µm nozzle orifice with a mean sphericity of 0,97. Hygroscopicity investigations reported a critical point at 40 % relative humidity where collapse of the microspheres occurred. The overall process yield was 92,1 ± 4,2 % on average.