Resistance to freezing and freeze-drying storage processes of probiotic bifidobacteria.

The resistance to freezing at –135 °C and freeze-drying of potentially probiotic bifidobacteria strains isolated from human habitat and from commercial probiotic products already present in the Italian market were tested. The analysis was conducted in two different cryoprotectives, sucrose and skim milk. The strains of Bifidobacterium animalis, the only species found in the commercial probiotic product, were resistant to freezing and freeze-drying in both of the cryoprotectives used. Bifidobacteria from human habitat, B 1501 and B 632 Bifidobacterium breve strains and B 600/2, B 669/3 and B 2416 Bifidobacterium catenulatum strains, resulted as the most resistant strains in the storage processes in both cryoprotectives. These strains are potentially useful for industrial applications. In the strains tested the percentage of viable cells were higher after freezing than after freeze drying. The performance of the cryoprotectives analysed were strain-dependent