Propionibacteria flora in Swiss raw milk from lowlands and Alps

Abstract

The propionic acid bacterial flora in Swiss raw milk was investigated. Four hundred and fifty-three strains from lowland milk and 21 strains from Alpine raw milk were classified to the species level by protein profile analysis and restriction analysis of the 23S ribosomal ribonucleic acid (rRNA). Plasmid profiles and random amplified polymorphic deoxyribonucleic acid (RAPD) was used to differentiate the strains. The flora was found to be extremely diverse. All four dairy Propionibacterium species were found in lowland raw milk: 71 % were P. freudenreichii, 19 % P. jensenii, 8 % P. acidipropionici and 2 % P. thoenii. P. acidipropionici was not found in alpine milk but P. freudenreichii made up 55 %, P. jensenii 15 % and P. thoenii 30 % of the total. Among 278 P. freudenreichii strains, 219 (79 %) different strains were identified by RAPD to the strain level. For the other species strain diversity was even greater. Only 30 % of the strains analyzed carried plasmids. The Swiss cheese industry has a large reservoir of Propionibacterium strains in raw milk for future applications and developments. © Inra/Elsevier, Paris.