Diacetyl and acetoin production by Lactobacillus casei.

Agitation of broth cultures of Lactobacillus casei retarded cellular dry weight accumulation but enhanced production of both diacetyl and acetoin. Addition of pyruvate overcame this retardation, but addition of sulfhydryl-protecting reagents did not. Both pyruvate and citrate enhanced accumulated dry weight of L. casei incubated without agitation, but only pyruvate increased diacetyl accumulation. Both actively dividing cells and cells suspended in buffer converted pyruvate to diacetyl and acetoin. Maximum production of diacetyl and acetoin occurred during the late logarithmic or early stationary phases. Cells isolated from pyruvate- or citrate-containing cultures showed the greatest ability to convert pyruvate to diacetyl and acetoin. The optimum pH for diacetyl and acetoin formation by whole cells was in the range of 4.5 to 5.5. The presence of citrate or acetate enhanced diacetyl and acetoin formation by L. casei cells in buffer suspension.