Defined Strains and Phage-Insensitive Mutants for Commercial Manufacture of Cottage Cheese and Cultured Buttermilk

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Abstract
The use of defined single strains and their phage-insensitive mutants as starters for cottage cheese and cultured buttermilk is discussed. A culture blend of 6 strains was used to manufacture consecutive vats of cottage cheese and eliminate culture rotations. Advantages of this culture system included elimination of starter failure, better product uniformity, more consistent starter activity and standardized make procedures. Individual strains in starter cultures also were used as antigens for a rapid detection test for lactic-streptococcal agglutinins in cheese milk. If sedimentation was encountered seasonally, individual agglutinin-sensitive strains were identified and replaced without need to replace an entire culture blend. New strains were pretested for sensitivity against cheese milk prior to their use in starters. Individual starter strains varied in their sensitivities to agglutinins in cheese milk and colostrum. Phage-infected strains were replaced with phage-insensitive mutants. Defined single strains and their phage-insensitive mutants were used successfully for cottage cheese and cultured buttermilk production for more than 2 yr.