Growth phase and growth medium effects on the peptidase activities of Lactobacillus helveticus

The effect of growth phase, growth medium and storage conditions on the peptidase activities of Lactobacillus helveticus DPC 4571 were examined. Cell free extracts (CFEs) were prepared from both mid-log and stationary phase cells grown in either 10% (w/v) reconstituted skim milk (RSM) or MRS pH 5.4 broth. In general, Lb. helveticus DPC 4571 was found to possess a broad range of aminopeptidase, dipeptidase, tripeptidase, endopeptidase and proline-specific peptidase activities. The stability of these peptidase activities in a CFE of Lb. helveticus DPC 4571 stored at 4°C was variable. The specific activities of the majority of these peptidases were significantly (P<0.05) influenced by both growth phase and growth medium. Cells grown to mid-log phase in RSM were found to have the highest level of peptidase activity.