Moisture requirements for growth and metabolite production by lactic Acid bacteria

The effect of water activity (a(w)) reduction on growth and acid and diacetyl production by three lactic streptococci was studied. In addition, the influence of low moisture conditions on several bacteria of significance in the fermentation of sauerkraut was examined. The minimal a(w) supporting growth of dairy lactics was 0.93 in a medium adjusted with glycerol. Media adjusted with sucrose generally were more inhibitory than those in which glycerol was the humectant. Titratable acidity, although not related to the type of humectant, did depend on the a(w) of the medium and was directly related to the extent of growth. Diacetyl concentration increased in cultures of reduced a(w) when the media were adjusted with both humectants; however, the effect was greatest with glycerol. A lactic strain associated with sauerkraut fermentation appeared to grow at a lower minimal a(w) in a glycerol-adjusted medium than in a system adjusted with NaCl; however, none of the sauerkraut organisms grew at a(w) levels of <0.95 when NaCl was the solute. Acid production appeared to be related to the presence and extent of growth at all of the a(w) levels studied.