Incorporation of bifidobacteria into probiotic formulations is promoted worldwide due to the health benefits associated with their application. For the manufacturing of such probiotic formulations, drying of microorganisms is an important process. Spray drying is a well-established and economical method for this purpose. Using spray drying, however, cells are exposed to stress, affecting their viability. The aim of this study was to generate a systemic knowledge about the impact of spray drying on the viability of B. bifidum BB-12. First, the effect of thermal stress was investigated by exposure of B. bifidum BB-12 to different temperatures in defined time intervals. The alterations in cell membrane integrity and esterase activity were studied using fluorimetry and compared to the heat response of the robust strain E. faecium M-74. Exposing microorganisms to the same temperatures, alterations in the viability of B. bifidum BB-12 occurred after shorter time intervals. Moreover, cell membrane damage and changes in the esterase activity were more rigorous, indicating the higher sensitivity of B. bifidum BB-12. Then, B. bifidum BB-12 was spray dried. The impact of spray drying on the changes in the membrane integrity and membrane potential was investigated using flow cytometry. Culturability was investigated using plate count method. Unprotected B. bifidum BB-12 was markedly harmed by the drying process, drastic membrane damage, depolarization and reduced culturability were observed. The protective impact of excipients on the cell damage during spray drying and one month storage was evaluated. Gum arabic, gelatin and pectin showed the best protective impact. Cells pre-treated with these excipients showed reduced membrane damage, enhanced stability and improved culturability during the storage time. Application of the gathered knowledge may contribute to develop rapid tools for investigation of the cell viability and to improve the production yield. © 2013 Elsevier Ltd.
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