Ultra-Low Temperature Storage of Lactic Streptococci

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Abstract
Cell viability, proteinase activity, and acid production for several single strain lactic streptococci were determined after storage at -20 C and -196 C. Cells in the late logarithmic growth phase were harvested from a casein, yeast extract glucose medium and the washed cells were suspended in 0.05 M phosphate buffer at pH 7.0. There were marked decreases in viability and biological activity of all cultures after 3 days of storage at -20 C which continued during the 60 day period of observation. Storage at -196 C permitted excellent survival of the cells and maintenance of biological activities.