RESPONSE OF CULTURES OF PROPIONIBACTERIUM TO ACID AND LOW PH - TOLERANCE AND INHIBITION

Seventeen Propionibacterium strains were tested for acid production an d final pH achieved on glucose, fructose, or maltose as the primary ca rbon source. On average, strains of Propionibacterium acidipropionici produced more acid and reached lower final pH values than did strains of the other species. Three strains of P. acidipropionici, one Propion ibacterium jensenii, and two Propionibacterium theonii strains were te sted further for the ability to survive and/or grow at low pH with lac tic, hydrochloric, or propionic acid as acidulant. The organic acids w ere mon inhibitory than hydrochloric acid; propionic acid was most inh ibitory. In all cases, the P. jensenii and P. thoenii strains initiate d growth and survived at lower pH values than did the P. acidipropioni ci strains. The ability to produce large amounts of acid or achieve lo w final pH values did not coincide with the ability to initiate growth or survive in low-pH conditions. Strains could not initiate growth be low pH 5.0, but cultures started at neutral pH reached final pH values of less than 4.4. At neutral pH, strains could grow in the presence o f increased lactate concentrations (up to 180 mM) or propionate concen trations (150 mM) that were inhibitory at acid pH. Attempts to isolate variants able to initiate growth below pH 5.0 were unsuccessful.