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Frozen Starters from Internal-pH-Control-Grown Cultures¹

Department of Microbiology

F. W. Bodyfelt

Department of Food Science and Technology Oregon State University, Corvallis 97331-3804

ABSTRACT

Frozen starters were prepared by growing and freezing unconcentrated individual Streptococcus cremoris strains in an internal-pH-control medium (PHASE 4). Frozen cultures were stored for 3 mo, with and without a cryoprotectant, and assayed monthly for cell viability and activity. Individual strains showed variations in their ability to survive storage at –20°C. Addition of glycerol helped preserve cell viability and activity at –20°C. Storage at –40 and –80°C in PHASE 4 preserved activity and viability without need of cryoprotectants. Unfrozen PHASE 4 cultures retained original activity and viability after 1 mo refrigerated storage. Frozen PHASE 4-grown starters have been used successfully in Cheddar and cottage cheese making for over 1 yr.

¹ Technical Paper No. 6427, Oregon Agricultural Experiment Station.