Effects of compatible solutes on cold tolerance of Propionibacterium freudenreichii and the significance of Propionibacterium cold tolerance in Swiss cheese manufacturing

Propionibacterium freudenriechii is one of the bacteria utilized in Swiss cheese starter cultures. Its carbon dioxide production is responsible for the development of the eyes commonly associated with Swiss cheese. The bacteria must endure high cook temperatures and low storage temperatures during ripening. Many bacteria are capable of synthesizing compatible solutes in response to different stresses. The primary focus of the present study was to determine the growth capabilities and transport of P. freudenreichii strains in the presence of exogenous glycine betaine, proline, and glutamate at low temperatures and evaluate the effects of storage temperature on eye formation in Swiss cheese manufactured with these dairy P. freudenreichii strains differing in low temperature growth abilities.; Four P. freudenreichii strains were grown in chemically defined media with the addition of 1 mM or 100 mM of glycine betaine, proline, or glutamate. The cultures were anaerobically incubated at 30, 22, 10, 7.2, and 4°C and spectrophometrically monitored to determine growth capabilities. Strains capable of growing at 10, 7.2, and 4°C were characterized as cold-tolerant and strains not able to grow at these temperatures were characterized as cold-sensitive. Compatible solute transport was assessed using 14C-labeled amino acids added to a cell suspension with a final concentration of 1 mM. The growth rate at the lowest temperature decreased and the lag phase increased for strains P843 and P57 and were therefore considered cold sensitive. At the same temperature the growth rate for strains P728 and P873 increased with a decreased lag phase. These strains were considered cold tolerant. All strains transported proline most abundantly at all temperatures with its cryoprotective effects observed at 22°, 10°, and 7.2°C by increased growth rates.; Swiss cheese was manufactured with a cold-tolerant strain (P873), a cold-sensitive strain (P572) and an intermediate strain (P196). All cheese blocks experienced identical warm room treatment (21°C for 17 days) but differed in cool ripening storage. The blocks were stored at 0, 4, or 7.2°C. Samples were taken at days 0, 30, 60, and 90. Counts of viable propionibacteria cells remained constant throughout the ripening treatment with a range of 108-9 . (Abstract shortened by UMI.)...