Abstract
A probiotic powder of poor flowability with high dust content, prepared by spray drying reconstituted skim milk fermented with Lactobacillus rhamnosus GG (LGG), was granulated by fluidized-bed granulation (FBG). The effects of the addition of skim milk powder (SMP) as a fluidizing aid, and of simple moisture-activation with or without dehydration, were investigated with respect to the performance of the FBG process. A fine, poorly fluidizable LGG powder (Geldart Group C) could be fluidized and granulated, with a 4- to 5-fold increase in particle size (d4,3 = 96–141 μm), by mixing with SMP (30–50%), which has larger, fluidizable particles belonging to Geldart Group A. Moisture-activation after the mixing, followed by fluidized-bed dehydration with hot air to remove excess moisture, further improved the FBG; the yield of the granules increased from 42% to 61% and the particle size distribution became much narrower, although the average particle size remained almost the same (d4,3 = 142 μm). These granules showed a popcorn-type structure in scanning electron microscopy images and encapsulated a sufficient level of viable LGG cells (1.6 × 108 CFU g−1). These granules also exhibited much better flowability and dispersibility than the spray-dried LGG powder.
Highlights
Spray drying often produces fine powders (
Our preliminary experiments indicated that the LRP was poorly fluidized and not suitable for fluidizedbed granulation (FBG)
This study demonstrated that LRP, consisting of fine and very poorly fluidizable particles (Geldart Group C), was successfully granulated (LRP-G1) when fluidized together with skim milk powder (SMP), which consists of larger, lighter, and well-fluidizable Geldart Group A particles
Summary
An effective way to minimize these issues is to enlarge the size of the powder particles using a four-step granulation process: wetting and nucleation, coalescence or growth, consolidation, and attrition or breakage [5]. A process involving the displacement of air on the particle surface with binding liquid, is one of the most popular granulation techniques used in industry [3,4,5,6]. HSWG is strongly influenced by the mechanical redispersion of the binding liquid by impellers and choppers, whereas FBG is primarily influenced by the wetting of particles with binding liquid [7]. The fine particles bind together via liquid bridges formed by the sprayed binding liquid, and the excess liquid is removed by simultaneous drying, resulting in the formation of large granules [8,9,10,11].
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