Stability of probiotic Lactobacillus paracasei during storage as affected by the drying method

The effects of drying technique on the storage stability of Lactobacillus paracasei subsp. paracasei CRL 431 in a whole milk powder matrix were investigated. Whole milk powder-bacteria mixtures were dried using spray drying, freeze drying and fluidised bed drying and stored at 25 °C under controlled water activity (aw values of 0.11, 0.33 and 0.52) for 105 d. At aw = 0.11, cell viability loss was minimal, while at aw = 0.52 viability was lost in all powders within 22 days. At the intermediate aw of 0.33, there were marked differences among stored powders. Improved bacterial viability at low aw across all the powders was probably due to lower amount of water and low molecular mobility in the matrix, as observed in the FT-IR and X-ray diffraction studies. Improved viability results of fluidised bed-dried powder were attributed to its low moisture content, resulting from its larger agglomerates with lower porosity.