Effect of additives on the viability of bifidobacteria loaded in alginate poly-l-lysine microparticles during the freeze-drying process

Bifidobacteria-loaded alginate poly-l-lysine microparticles (bap microparticles) were prepared using an air atomization method and then freeze-dried. The viability of the bap microparticles was investigated as a function of the amount of the bifidobacteria cultures, and the addition of a yeast extract, cryoprotectants, antioxidants and neutralizer. The size of the bap microparticles with and without the bifidobacteria was 84.8 +/- 28.5 mu m (mean +/- standard deviation) and 113.1 +/- 38.5 mu m, respectively. The surface morphology was slightly ellipsoid and wrinkled regardless of the incorporating bifidobacteria. The viability gradually decreased with increasing freeze-drying time. Free-flowing powdered, bap microparticles were obtained at least 12 h after freeze-drying the wetted slurry of bap microparticles. However, the particles tended to aggregate when either lactose or ascorbic acid was added. The addition of a yeast extract, cryoprotectants (glycerol and lactose), antioxidants (NaHSO3 and ascorbic acid) and neutralizer (Mg-3(PO4)(2)) resulted in a significantly higher viability of the bifidobacteria in the bap microparticles after freeze-drying (0.34-1.84 log) compared with the culture alone.