Fluidized-Bed Granulation of Probiotics-Encapsulated Spray-Dried Skim Milk Powder: Effects of a Fluidizing Aid, Moisture-Activation and Dehydration

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 (d(4,3) = 96-141 mu m), 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 (d(4,3) = 142 mu m). These granules showed a popcorn-type structure in scanning electron microscopy images and encapsulated a sufficient level of viable LGG cells (1.6 x 10(8) CFU g(-1)). These granules also exhibited much better flowability and dispersibility than the spray-dried LGG powder.

Automated summary

The probiotic powder of poor flowability prepared by spray drying reconstituted skim milk fermented with Lactobacillus rhamnosus GG was granulated using fluidized-bed granulation. The addition of skim milk powder and moisture activation improved the performance of the granulation process, leading to increased yield and narrower particle size distribution. The granules showed a popcorn-type structure and contained viable LGG cells, exhibiting better flowability and dispersibility than the original spray-dried powder.